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FOWNES 


MANUAL  OF  CHEMISTRY. 


-^ 


^C   J>h&f/-»-~^  f^   f'  ^i 


NTARY 


CHEMISTRY, 


THEORETICAL   AND    PEACTICAL 

BY  ^ 

GEORGE  FOWNES,  F.R.S., 

lATS  PROFESSOK  OF  PBAX3TICAL  CHXMISTRT  IN  CNIVEBSITX  COLLEGE,  LONSOir. 

EDITED,  WITH  ADDITIONS, 

BT 

ROBERT   BRIDGES,   M.  D., 

PR0PES80E  OF  CHEMISTRY  IX  THE  PHILADELPHIA  COLLEQB  OF  PHARMACT,  ETC.  ETC. 


WITH  NUMEROUS  ILLUSTRATIONS  ON  WOOD. 


PHILADELPHIA: 
BLANCHARD    AND    LEA 
1857. 

1^ 


Entered,  according  to  Act  of  Congress,  in  the  year  1863,  by 
BLANCHARD   AND   LEA, 

in  the  Clerk's  Office  of  the  District  Court  of  the  United  States  for  the 
Eastern  District  of  Pennsylvania. 

COLLINS,  PRINTER 


ADVERTISEMENT 

TO  THE 

NEW  AMERICAN   EDITION 


The  lamented  death  of  the  Author  has  caused  the  revision  of  this 
edition  to  fall  into  the  hands  of  others,  who  have  fully  sustained  its 
reputation  by  the  additions  which  they  have  made,  more  especially 
in  the  portion  devoted  to  Organic  Chemistry,  as  set  forth  in  their 
preface.  This  labour  has  been  so  thoroughly  performed,  that 
the  American  Editor  has  found  but  little  to  add,  his  notes  con- 
sisting chiefly  of  such  matters  as  the  rapid  advance  of  the  science 
has  rendered  necessary,  or  of  investigations  which  had  apparently 
been  overlooked  by  the  Author's  friends.  These  additions  will  be 
found  distinguished  by  his  initials. 

The  volume  is  therefore  again  presented  as  an  exponent  of  the 
most  advanced  state  of  Chemical  Science,  and  as  not  unworthy  a  con- 
tinuation of  the  marked  favour  which  it  has  received  as  an  elementary 
text-book. 

Philadelphia, 

October,  1853. 

1*  (T) 


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PREFACE 


The  design  of  the  present  volume  is  to  offer  to  the  student  com- 
mencing the  subject  of  Chemistry,  in  a  compact  and  inexpensive 
form,  an  outline  of  the  general  principles  of  that  science,  and  a  history 
of  the  more  important  among  the  very  numerous  bodies  which  Che 
mical  Investigations  have  made  known  to  us.  The  work  has  no  pre- 
tensions to  be  considered  a  complete  treatise  on  the  subject,  but  is 
intended  to  serve  as  an  introduction  to  the  larger  and  more  compre- 
hensive systematic  works  in  our  own  language  and  in  those  of  the 
Continent,  and  especially  to  prepare  the  student  for  the  perusal  of 
original  memoirs,  which,  in  conjunction  with  practical  instruction  in 
the  laboratory,  can  alone  afford  a  real  acquaintance  with  the  spirit  of 
research  and  the  resources  of  Chemical  Science. 

It  has  been  my  aim  throughout  to  render  the  book  as  practical  as 
possible,  by  detailing,  at  aa  great  length  as  the  general  plan  permitted, 
many  of  the  working  processes  of  the  scientific  laboratory,  and  by 
exhibiting,  by  the  aid  of  numerous  wood-engravings,  the  most  useful 
forms  of  apparatus,  with  their  adjustments  and  methods  of  use. 

As  one  principal  object  was  the  production  of  a  convenient  and 
useful  class-book  for  pupils  attending  my  own  lectures,  I  have  been 
induced  to  adopt  in  the  book  the  plan  of  arrangement  followed  in 
the  lectures  themselves,  and  to  describe  the  non-metallic  elements 
and  some  of  their  most  important  compounds  before  discussing  the 
subject  of  the  general  philosophy  of  Chemical  Science,  and   even 

(yii) 


VIU  PREFACE. 

before  describing  the  principle  of  the  equivalent  quantities,  or  ex- 
plaining the  use  of  the  written  symbolical  language  now  universal 
among  chemists.  For  the  benefit  of  those  to  whom  these  matters 
are  already  familiar,  and  to  render  the  history  of  the  compound  bodies 
described  in  the  earlier  part  of  the  work  more  complete,  I  have  added 
in  foot-notes  the  view  adopted  of  their  Chemical  constitution,  ex- 
pressed in  symbols. 

I  have  devoted  as  much  space  as  could  be  afforded  to  the  very  im- 
portant subject  of  Organic  Chemistry ;  and  it  will,  I  believe,  be  found 
that  there  are  but  few  substances  of  any  general  interest  which  have 
been  altogether  omitted,  although  the  very  great  number  of  bodies  to 
be  described  in  a  limited  number  of  pages  rendered' it  necessary  to 
use  as  much  brevity  as  possible. 

GEO.  FOWNES. 

Univebsitt  CoLLEaE,  London, 
October  5,  1847. 


ADVERTISEMENT 


TO  THE 


THIRD  LONDON  EDITION, 


The  correction  of  this  Edition  for  the  press  was  the  daily  occupa- 
tion of  Professor  Fownes,  until  a  few  hours  previous  to  his  death  in 
January,  1849. 

His  wish  and  his  endeavour,  as  seen  in  his  manuscript,  were  to 
render  it  as  perfect  and  as  minutely  accurate  as  possible. 

When  he  had  finished  the  most  important  part  of  the  Organic 
Chemistry,  where  the  most  additions  were  required,  he  told  me  he 
should  "do  no  more," — he  had  "finished  his  work." 

At  his  request  I  have  corrected  the  press  throughout,  and  made  a 
few  alterations  that  appeared  desirable  in  the  only  part  which  he  had 
left  unaltered,  the  Animal  Chemistry. 

The  index  and  the  press  have  also  been  corrected  throughout  by 
his  friend  Mr.  Robert  Murray. 


H   Bence  Jones,  M.D. 


),  Geosvknok  Stebet, 
Jan.y  1850. 


(ix) 


ADVERTISEMENT 


TO   THE 


FOURTH   LONDON  EDITION 


It  has  been  the  endeavour  of  the  Editors  to  include  in  the  present 
edition  of  the  Manual  the  progress  of  Chemistry  since  the  Author's 
death. 

The  foundation  which  he  laid,  and  the  form  which  he  gave  to  the 
work,  remain  untouched.  But  time  has  rendered  it  necessary  that 
each  portion  should  be  revised ;  and  a  few  repairs,  and  some  consider-* 
able  additions,  especially  in  Organic  Chemistry,  have  been  made. 
Thus,  several  of  the  chapters  on  the  Alcohols,  the  Organic  Bases, 
Colouring  Matters,  &c.,  have  been  almost  re-written. 

Still,  such  changes  only  have  been  made  as  the  Editors  believed 
the  Author  himself  would  have  desired,  if  his  life  had  been  spared 
to  Science. 

H.  Bence  Jones. 

A.   W.   HOFMANN. 
«    London,  September,  1852. 


(^) 


TABLE   OF    CONTENTS, 


PAGI 

Introduction 25 


PART    I. 
PHYSICS. 

Of  densitt  and  specific  gravity. 

Methods  of  determining  the  specific  gravities  of  fluids  and  solids 27 

Construction  and  application  of  the  hydrometer 32 

Of   the    physical   constitution   op  the  atmosphere,  and   of  gases   in 

GENERAL. 

Elasticity  of  gases. — Construction  and  use  of  the  air-pump 34 

Weight  and  pressure  of  the  air. — Barometer 37 

Law  of  Mariotte;   relations   of  density  and  elastic  force;   correction   of 

volumes  of  gases  for  pressure 38 

Heat. 

Expansion. — Thermometers 41 

Different  rates  of  expansion  among  metals;  compensation-pendulum 44 

Daniell's  pyrometer 45 

Expansion  of  liquids  and   gases. — Ventilation. — Movements  of  the  atmo- 
sphere   46 

Conduction  of  heat 62 

Change  of  state. — Latent  heat 52 

Ebullition;  steam 54 

Distillation 58 

Evaporation  at  low  temperatures 59 

Vapour  of  the  atmosphere;  hygrometry 61 

Liquefaction  of  permanent  gases 62 

Production  of  cold  by  evaporation 64 

Capacity  for  heat. — Specific  heat 66 

Sources  of  heat 68 

2  ,  (xiii) 


XIV  CONTENTS. 

LiaHT. 

PAOB 

Reflection,  refraction,  and  polarization  of  light 71 

Chemical  rays 77 

Kadiation,  reflection,  absorption,  and  transmission  of  heat 79 

Magnetism. 

Magnetic  polarity;  natural  and  artificial  magnets 86 

Terrestrial  magnetism 88 

Electricitt.  "* 

Electrical  excitation;  machines 92 

Principle  of  induction ;  accumulation  of  electricity 93 

Voltaic  electricity 97 

Thermo-electricity  .-^Animal  electricity 99 

Electro-magnetism;  magneto-electricity 100 

Electricity  of  steam 10? 


PART   II. 

CHEMISTRY  OF  THE  ELEMENTARY  BODIES. 

NON-HETALLIC  ELEMENTS. 

Oxygen 105 

Hydrogen;  water;  binoxide  of  hydrogen  110 

Nitrogen;  atmospheric  air ;  compounds  of  nitrogen  and  oxygen 120 

Carbon;  carbonic  oxide ;  carbonic  acid  127 

Sulphur;  compounds  of  sulphur  and  oxygen '. 131 

Seleniuip 136 

Phosphorus;  compounds  of  phosphorus  and  oxygen 137 

Chlorine;  hydrochloric  acid. — Compounds  of  chlorine  and  oxygen 139 

Iodine 143 

Bromine 148 

Fluorine 149 

Silicium 150 

Boron 151 

COMPOTTNDS    FORMED   BY  THE    UNION   OP   THE   NON-METALLIC    ELEMENTS   AMONG 
THEMSELVES.  ' 

Compounds  of  carbon  and  hydrogen. — Light  carbonetted  hydrogen ;  olefiant 

gas;  coal  and  oil-gases. — Combustion,  and  the  structure  of  flame 163 

Nitrogen  and  hydrogen;  ammonia 162 


CONTENTS.  XV 

PA.GB 

Sulphur,  selenium,  and  phosphonis,  with  hydrogen 163 

Nitrogen,  with  chlorine  and  iodine;  chloride  of  nitrogen 167 

Other  compounds  of  non-metallic  elements 168 

Chlorine,  with  sulphur  and  phosphorus 168 

Dn  the   GENSBAL  PBUtCIPLES   OF  CHEKICAL  PHILOSOPHT. 

Komenclature 170 

Laws  of  combination  by  weight 172 

By  volume 177 

Chemical  symbols ISO 

The  atomic  theory 182 

Chemical  affinity 183 

Electro-chemical  decomposition;  chemistry  of  the  voltaic  pile 187 

Metals. 

General  properties  of  the  metals 197 

Crystallography 202 

Isomorphism 209 

Polybasic  acids 212 

Binary  theory  of  the  constitution  of  salts 213 

Potassium 217 

Sodium 224 

Ammonium 232 

Lithium 235 

Barium 237 

Strontium 239 

Calcium 239 

Magnesium 245 

Aluminium 248 

Beryllium  (glucinum) 250 

Yttrium,  cerium,  lanthanium,  and  didymium 251 

Zirconium.  —  Thorium  , 252 

Manufacture  of  glass,  porcelain,  and  earthenware 252 

Manganese 25G 

Iron 259 

Aridium 206 

Chromium 267 

Nickel 269 

Cobalt 271 

Zinc 272 

Cadmium 274 

Bismuth 274 

Uranium 276 

Copper 277 

Lead 279 

Tin 2S2 


XVl  CONTENTS. 


Tungnten , 284 

Molybdenum 284 

Vanadium 285 

Tantalum  (columbium) 286 

Niobium  and  pelopium 286 

Titanium 287 

Antimony 287 

Tellurium 290 

Arsenic 291 

Silver 296 

Gold 299 

Mercury 301 

Platinum 307 

Palladium 311 

Rhodium 312 

Iridium 312 

Euthenium 314 

Osmium 314 


PART   III. 
ORGANIC  CHEMISTRY. 

Introduction 316 

Law  of  substitution 317 

The  ultimate  analysis  op  organic  bodies 320 

Empirical  and  rational  formuljs 329 

Determination  op  the  density  op  the  vapours  op  volatile  liquids  ....  330 
Saccharine  and  amylaceous  substances,  and  the  products  op  their 

alteration 333 

Cane  and  grape-sugars  j  sugar  from  ergot  of  rye  ,•  sugar  of  diabetes  insipi- 
dus; liquorice-sugar;  milk-sugar;  mannite 333 

Starch ;  dextrin ;  starch  from  Iceland-moss ;  inulin ;  gum ;  pectin ;  lignin ..  337 

Oxalic  and  saccharic  acids 341 

Xyloidin;  pyroxylin;  mucic  acid 344 

Suberic,  mellitic,  rhodizonic,  and  croconic  acids 345 

Fermentation  of  sugar.  —  Alcohol 345 

Lactic  acid 349 

Ether,  and  ethyl-compounds 361 

Sulphovinic,  phosphovinic,  and  oxalovinic  acids 358 

Heavy  oil  of  wine 362 

Olefiantgas;  Dutch  liquid;  chlorides  of  carbon 362 


CONTENTS.  XTll 

PAOB 

Ethionio  and  isethionio  acids 365 

Chloral,  &o 366 

Mercaptan  ;  xanthic  acid 367 

Aldehydej  aldehydic  acid;  acetal 369 

Acetic  acid 371 

Chloracetic  acid 375 

Acetone 376 

Kakodyl , 377 

Substances  hore  or  less  allied  to  alcohol. 

Wood-spirit;  methyl-compounds 381 

Sulphomethylic  acid 384 

Formic  acid;  chloroform 385 

Formomethylal ;  methyl-mercaptan 387 

Potato-oil  and  its  derivatives 388 

Sulphamylic  acid;   valerianic  acid 390 

Chlorovalerisic  and  chlorovalerosio  acids 393 

Fusel-oil  from  grain-spirit;  general  view  of  the  alcohols 393 

Bitter-almond-oil  and  its  products;   benzoyl-compounds 396 

Benzoic-acid ;  sulphobenzoic  acid ;  benzone  and  benzol 396 

Sulphobenzide  and  hyposulphobenzio  acid 398 

Nitrobenzol,  azobenzol,  &c 399 

Formobenzoic  acid;   hydrobenzamide ;    benzoin;   benzile;    benzilio  acid; 

benzimide,  &c ; 400 

Hippuric  acid 402 

Homologues  of  benzoyl-series 403 

Salicin;  salicyl  and  its  compounds 403 

Chlorosamide.  —  Phloridzin.  —  Cumarin 405 

Cinnamyl  and  its  compounds ;  cinnamic  acid ;  chloro-cinnose 407 

Vegetable  acids. 

Tartaric  acid 410 

Racemic  acid 413 

Citric  acid 413 

Aconitic  or  equisetic  acid 411 

Malic  acid 414 

Fumaric  and  maleic  acids 416 

Tannic  and  gallic  acids 416 

AZOTIZED   ORGANIC    PRINCIPLES    OP   SIMPLE    CONSTITUTION. 

Cyanogen;  paracyanogen ;  hydrocyanic  acid 420 

Amygdalin;  amygdalic  acid 423 

Metallic  cyanides 424 

Cyanic,  cyanuric,  and  fulminic  acids 426 

Chlorides,  Ac^,  of  cyanogen 429 

2* 


XVlll  CONTENTS. 

PAGE 

Ferro-  and  .Wricyanogen,  and  their  compounds;  Prussian  blue 430 

Cobaltocyanogen ;  nitroprussides 433 

Sulphocyanogen,  and  its  compounds ;  selenocyanogen ;  melam ;  melamine ; 

ammeline;  ammelide , 434 

Urea,  and  uric  acid 436 

Allantoinj   alloxan;    alloxanic  acid;    mesoxalio  acid;    mykomelinio  acid; 

parabanic  acid ;    oxaluric  acid ;    thionuric  acid ;    uramile ;    alloxan  tin ; 

murexide;  murexan 438 

Xanthio  and  cystic  oxides 443 

The  vegkto-alkalis,  and  allied  bodies. 

Morphine,  and  its  salts 444 

Narcotine;  opianio  and  hemipinic  acids ;  cotarnine 445 

Codeine;  thebaine;  pseudo-morphine;  narceine;  meconine 446 

Meconic  acid 446 

Cinchonine  and  quinine;  quinoidine 447 

Kinio  acid;  kinone;  hydrokinone 448 

Strychnine  and  brucine  ;  veratrine 449 

Conicine;    nicotine;    sparteine;   harmaline;   harmine;   caffeine  or  theine; 

theobromine;    berberine ;   piperine;    hyoscyamine;    atropine;    solanine; 

aconitine;  delphinine;  emetine;  curarine 450 

Gentianin;  populin;  daphnin ;   hesperidin;   elaterin;  antiarin;  picrotoxin; 

asparagin  ;  santonin 451 

Organic  bases  op  artificial  origin. 

Bases   of   the    ethyl-series.  —  Ethylamine  ;   biethylamine  ;   triethylamine  j 

oxide  of  tetrethyl-ammonium , 455 

Bases  of  the  methyl-series.  —  Methylamine;   bimethylamine;   trimethyla- 

mine;   oxide  of  tetramethyl-ammonium 457 

Bases   of   the   amyl-series.  —  Amylamine  ;    biamylamine  ;    triamylamine  ; 

oxide  of  tetramyl-ammonium 468 

Bases  of  the  phenyl-series.  —  Aniline;  chloraniline ;  nitraniline;  cyaniline; 

melaniline 459 

Bases  homologous  to  aniline.  —  Toluidine ;  xylidine ;  cumidine.    Naphthali- 

dine;  chloronicine 462 

Mixed  bases.  —  Ethylaniline;  biethylaniline  ;  oxide  of  triethylamyl-ammo- 

nium  ;    biethylamylamine  ;    oxide   of   methylobiethylamyl-ammonium  ; 

methylethylamylamine ;  ethylamylaniline ;  oxide  of  methyl-ethyl-amylo- 

phenyl-ammonium 463 

Bases  of  uncertain  constitution. 

Chinolin* T. 464 

Kyanol;  leucol;  picoline 465 

Petinine 466 

Furfurine 465 


CONTENTS.  XIX 

PAQB 

Fucusine;  amarine;  thiosinnamine 466 

Thialdinoj  alanine 467 

Phosphorus-bases 468 

Antimony-bases  469 

Organic  colouring  principles. 

Indigo;  white  indigo;  sulphindylic  acid 470 

Isatin;  anilic  and  picric  acids ;  chrysanilio  and  anthranilic  acids 471 

Litmus — lecanorin;  orcin;  orcein,  Ac 474 

Cochineal,  madder,  dye-woods,  Ac 477 

Chrysammic,  chrysolepic,  and  styphnic  acids 479 

QiLS  and  fats. 

Fixed  oils ;  margarin,  stearin,  and  olein ;   saponification,  and  its  products ; 

glycerin  • •••••  480 

Palm  and  cocoa-oils.  — Elaidin  and  elaidic  acid 483 

Suberic,  succinic,  and  sebacic  acids 484 

Butter. — Butyric,  caproic,  caprylic,  and  capric  acids 485 

Wax;  spermaceti;  cholesterin;  cantharidin 486 

Acrolein;  acrylic  acid 487 

Products  of  the  action  of  acids  on  fats 487 

Ca«tor-oU;  caprylic  alcohol 488 

Volatile  eila.  —  Oile  of  turpentin,  lemons,  aniseed,  cumin,  cedar,  gaultheria, 

valerian,  peppermint,  lavender,  rosemary,  orange-flowers,  rose-petals 488 

Camphor;  camphoric  acid 492 

Oils  of  mustard,  garlic,  onions,  Ac 492 

Resins.  —  Caoutchouc 493 

Balsams.  —  Toluol,  styrol 494 

Components  op  the  animal  body. 

Albumin,  fibrin,  and  casein;  protein 496 

Gelatin  and  chondrin 600 

Kreatin  and  kreatinine •. 602 

Coojposition  of  the  blood ;  respiration;  animal  heat 603 

Chyle;  lymph;  mucus;  pus 507 

Milk;  bile;  urine;  urinary  calculi 608 

Nervous  substance ;  membranous  tissue ;  bones 616 

The  function  of  nutrition  in  the  vegetable  and  animal  kingdoms 618 

Products    op   the    destructive    distillation,   and    slow   putbefactivi: 

CHANGE    OP   organic   MATTER. 

Bubstances  obtained  from  tar.  —  Paraffin;  eupione;   picamar;   kapnomorj 
cedriret;  kreosote;  chrysen  and  pyren , 623 


XX  CONTENTS. 

,  PAQH 

Coal-oil. —  Carbolic  acid  (hydrato  of  oxide  of  phenyl) 626 

Naphthalin  and  paranaphtballn 529 

Petroleum,  naphtha,  and  other  allied  substances 530 

A.PPENDIX. 

Hydrometer  tables.  —  Table  of  the  tension  of  the  vapour  of  water  at  differ- 
ent temperatures.  —  Table  of  the  proportion  of  real  alcohol  in  spirits 
of  different  densities.  —  Analyses  of  the  mineral  waters  of  Germany. — 
Table  of  weights  and  measures 533 


LIST  OF  ILLUSTRATIONS 
BY  WOOD-CUTS. 

Fig.  Pago 

1  Specific-gravity  bottle 28 

2  "            "                29 

3  "  "  *29 

4  "            *•                « 39 

5  "            * 10 

6  "           •*      beads 31 

7  Hydrometer 32 

8  Urinometer 32 

9  Specific  gravity 33 

10  Elasticity  of  gases 34 

11  Single  air-pump 35 

12  Double      "         36 

13  Improved"         36 

14  "        "         Z7 

15  Barometer 38 

16  "         39 

17  "         40 

18  Expansion  of  solids 41 

19  "                liquids  41 

20  "               gases 41 

21  Differential  thermometer 43 

22  "                   «             43 

23  Difference  of  expansion  in  metals  44 

24  Gridiron  pendulum 44 

25  Mercury         "         45 

26  Compensation  balance 45 

27  Daniell*s  pyrometer 45 

28  Expansion  of  mercury 47 

29  Atmospheric  currents 50 

30  «                 «        50 

31  "                  "        51 

32  Boiling  paradox 55 

.S3  Steam-bath 57 

34  Steam-engine 57 

35  Distillation 66 

36  Liebig's  condenser 59 

37  Tension  of  vapour 69 

38  "                 "       60 

89  Wet-bulb  hygrometer 62 

(xxi) 


XXll  LIST    OP    ILLUSTRATIONS. 

40  Condensation  of  gases 63 

41  Thilorier's  apparatus „ 64 

42  Cold  by  evaporation 65 

43  Wollaston's  cryophorus 65 

44  Daniell's  hygrometer 65 

45  Keflection  of  light 72 

46  Refraction  of  light 72 

47  "  " 72 

48  "  " 73 

49  Spectrum 74 

50fc       «        74 

51  Polarization  of  light 75 

62  "  "       .) 76 

63  "  " 76 

64  Reflection  of  heat 79 

66  «  "     80 

56  Effects  of  electrical  current  on  the  magnetic  needle 82 

67  «  "  "  "  82 

58  Current  produced  by  heat 83 

69  Melloni's  instrument  for  measuring  transmitted  heat 83 

60  Magnetic  polarity 87 

61  "  "       87 

62  Electro  repulsion 93 

63  Electroscope 93 

64  Electric  polarity 93 

66  Electrical  machine 95 

66  "  "       plate 95 

67  Leyden  jar 96 

68  Electrophorus 97 

69  Volta'spile 98 

70  Crown  of  cups 98 

71  Cruikshank's  trough 99 

72  Effect  of  electrical  current  on  the  magnetic  needle 100 

73  Astatic  needle 101 

74  Magnetism  developed  by  the  electrical  current 101 

75  "  "  "  " 102 

76  Electro-magnet 102 

77  Apparatus  for  oxygen 105 

78  Hydro-pneumatic  trough 106 

79  Transferring  gases 107 

80  Pepy's  hydro-pneumatic  apparatus 107 

81  Apparatus  for  hydrogen Ill 

82  Levity  of  hydrogen  Ill 

83  Diffusion  of  gases 112 

84  Daniell's  safety-jet 113 

85  Musical  sounds  by  hydrogen 114 

U  Cataly*'c  effect  of  platinum 115 


LIST    OF    ILLUSTRATIONS.  XXlll 

Fig.  l^age 

87  Decomposition  of  water 116 

88  Eudiometer  of  Cavendish 116 

89  Analysis  of  water •  • 116 

90  Preparation  of  nitrogen 120 

91  Analysis  of  air 121 

92  Ure's  eudiometer 122 

93  Preparation  of  nitric  acid 123 

94  "  protoxide  of  nitrogen 125 

95  Crystalline  form  of  carbon 127 

96  "  "  "  127 

97  «  "  «  f27 

98  "  "  "  « 127 

99  Preparation  of  carbonic  acid 129 

100  Mode  of  forming  caoutchono  connecting-tubes 129 

101  Crystalline  form  of  sulphur 131 

102  Crystals  of  sulphur 131 

103  Crystalline  form  of  sulphur 131 

104  Preparation  of  phosphorus ^137 

105  «  chlorine ^ 139 

106  "  hydrochloric  acid  142 

107  Safety-tube 143 

108  Combustible  under  water 145 

109  Preparation  of  hydriodic  acid 147 

110  «  silica - 150 

HI  Blast  furnace 167 

112  Reverberatory  furnace  157 

113  Structure  of  flame 158 

114  Mouth  blowpipe 159 

115  Structure  of  blowpipe  flame 159 

116  Argand  spirit-lamp 159 

117  Common        "  159 

118  Mitchell's      « 16C 

119  Gas  « 16C 

120  Davy's  safe    "  t 161 

121  Hemming's  safety-jet 161 

122  Effect  of  metallic  coil 161 

123  Apparatus  for  sulphuretted  hydrogen 16< 

124  Multiple  proportions 18i 

125  Water  in  its  usual  state 18J 

126  "      undergoing  electrolysis 189 

127  Voltameter 190 

128  Decomposition  without  contact  of  metals 191 

129  Wollaston's  voltaic  battery 193 

130  Daniell's  constant       «        193 

131  Grove's  *•  "        194 

132  Electrotype 195 

133  Lead-tree  295 


XXIV  LIST    OP    ILLUSTRATIONS. 

Fig.  Page 

134  Wire-drawing 198 

135  Wollaston's  goniometer 203 

136  Reflecting  "  204 

137  "  "  principles  of '. ...205 

138  Crystals,  regular  system 206 

139  "       regular  prismatic  system 206 

140  "       right  prismatic  system  207 

141  "       oblique  prismatic  system 207 

142  "       doubly  oblique  prismatic  system 208 

143  Crystals,  rhombohedral  system 208 

144  "       passage  of  cube  to  octahedron 209 

145  "       «         "      octahedron  to  tetrahedron 200 

146  Alkalimeter 227 

147  Apparatus  foi  determining  carbonic  acid 228 

148  "  "  "  "  "     229 

149  Iron  manufacture.    Blast-furnace 264 

150  Crystals  of  arsenious  acid 293 

151  Subliming  tube  for  arsenic 294 

152r  Marsh's  test 295 

153  Weighing  tube  321 

154  Combustion .- 321 

155  Chauffer 322 

156  Water  tube '. 322 

157  Carbonic  acid  bulbs 322 

158  Apparatus  complete 323 

159  Bulb  for  liquids 324 

160  Comparative  determination  of  nitrogen 325 

161  Pipette 325 

162  Absolute  estimation  of  nitrogen 326 

163  Varentrap's  and  Will's  method 327 

164  Determination  of  the  density  of  vapours 330 

165  Starch  granules 338 

166  Preparation  of  ether 361 

167  «  defiant  gas  ...., 363 

168  "  Dutch  liquid 363 

169  Catalysis 371 

170  Preparation  of  kakodyle 379 

171  "  benzoic  acid.... 397 

172  «  tannic  acid 417 

173  Uric  acid  crystals 438 

174  Blood  globules 504 

\Sb  Pus  "         608 

176  Milk        "         508 

177  Trommer's  test 514 

178  Uric  acid  calculus 515 

179  Urate  of  ammonia  calculus 515 

180  Pusiblo  calculus 516 

181  Mulberry  calculus 516 


MANUAL  OF  CHEMISTRY 


INTRODUCTION. 

Thb  Science  of  Chemistry  has  for  its  object  the  study  of  the  nature  and 
properties  of  all  the  materials  which  enter  into  the  composition  or  structure 
of  the  earth,  the  sea,  and  the  air,  and  of  the  various  organized  or  living  be- 
ings which  inhabit  these  latter.  Every  object  accessible  to  man,  or  which 
may  be  handled  and  examined,  is  thus  embraced  by  the  wide  circle  of 
Chemical  Science. 

The  highest  efforts  of  Chemistry  are  constantly  directed  to  the  discovery 
of  the  general  laws  or  rules  which  regulate  the  formation  of  chemical  com- 
pounds, and  determine  the  action  of  one  substance  upon  another.  These 
laws  are  deduced  from  careful  observation  and  comparison  of  the  properties 
and  relations  of  vast  numbers  of  individual  substances ; — and  by  this  method 
alone.  The  science  is  entirely  experimental,  and  all  its  conclusions  the  re- 
sults of  skilful  and  systematic  experimental  investigation. 

The  applications  of  the  discoveries  of  Chemistry  to  the  arts  of  life,  and 
to  the  relief  of  human  suflFering  in  disease,  are,  in  the  present  state  of  the 
science,  both  very  numerous  and  very  important,  and  encourage  the  hope 
of  still  greater  benefits  from  more  extended  knowledge  than  that  now 
enjoyed. 

In  ordinary  scientific  speech  the  term  chemical  is  applied  to  changes  which 
permanently  affect  the  properties  or  characters  of  bodies,  in  opposition  to 
effects  termed  physical,  which  are  not  attended  by  such  consequences. 
Changes  of  decomposition  or  combination  are  thus  easily  distinguished  from 
those  temporarily  brought  about  by  heat,  electricity,  magnetism,  and  the 
attractive  forces,  whose  laws  and  effects  lie  within  the  province  of  Physics 
or  Natural  Philosophy. 

Nearly  all  the  objects  presented  by  the  visible  world  are  of  a  compound 
nature,  being  chemical  compounds,  or  variously  disposed  mixtures  of  chem- 
3  (26) 


26  INTEODUCTION. 

ical  compounds,  capable  of  being  resolved  into  simpler  forms  of  matter. 
Thus,  a  piece  of  limestone  or  marble  by  the  application  of  a  red-heat  is  de- 
composed into  quicklime  and  a  gaseous  body,  carbonic  acid.  Both  lime 
and  carbonic  acid  are  in  their  turn  susceptible  of  decomposition,  the  first 
into  a  metal,  calcium,  and  oxygen,  and  the  second  into  carbon  and  oxygen. 
For  this  purpose,  however,  simple  heat  does  not  suffice,  the  resolution  of 
these  substances  into  their  components  demanding  the  exertion  of  a  high 
degree  of  chemical  energy.  Beyond  this  second  step  of  decomposition  the 
efforts  of  Chemistry  have  hitherto  been  found  to  fail,  and  the  three  bodies, 
calcium,  carbon,  and  oxygen,  having  resisted  all  attempts  to  resolve  them 
into  simpler  forms  of  matter,  are  accordingly  admitted  into  the  list  of  ele- 
ments ; — not  from  any  belief  in  their  real  oneness  of  nature,  but  from  the 
absence  of  any  evidence  that  they  contain  more  than  one  description  of 
matter. 

The  partial  study  of  certain  branches  of  Physical  Science,  as  the  physical 
constitution  of  gases,  the  chief  phenomena  of  heat  and  electricity,  and  a 
few  other  subjects,  forms  such  an  indispensable  introduction  to  Chemistry 
itself,  that  it  is  never  omitted  in  the  usual  courses  of  oral  instruction.  A 
sketch  of  these  subjects  is,  in  accordance  with  these  views,  placed  at  the 
commencement  of  the  present  volume. 


PART  I.— PHYSICS. 

OF  DENSITY  AND  SPECIFIC  GRAVITY. 

It  is  of  great  importance  in  the  ontset  to  trnderstand  clearly  what  is  meant 
by  the  terms  density  and  specific  gravity.  By  the  density  of  a  body  is  meant 
its  mass,  or  quantity  of  matter,  compared  with  the  mass  or  quantity  of  matter 
of  an  equal  volume  of  some  standard  body,  arbitrarily  chosen.  Specific 
gravity  denotes  the  weight  of  a  body,  as  compared  with  the  weight  of  an 
equal  bulk,  or  volume,  of  the  standard  body,  which  is  reckoned  as  unity.* 
In  all  cases  of  solids  and  liquids  this  standard  of  unity  is  pure  water  at  the 
temperature  of  60°  Fahr.  (15°-5C).  Anything  else  might  have  been  chosen; 
there  is  nothing  in  water  to  render  its  adoption  for  the  purpose  mentioned 
indispensable ;  it  is  simply  taken  for  the  sake  of  convenience,  being  always 
at  hand,  and  easily  obtained  in  a  state  of  perfect  purity.  The  ordinary  ex- 
pression of  specific  weight,  therefore,  is  a  number  expressing  how  many 
times  the  weight  of  an  equal  bulk  of  water  is  contained  in  the  weight  of 
the  substance  spoken  of.  If,  for  example,  we  say  that  concentrated  oil  of 
vitriol  has  a  specific  gravity  equal  to  1  '85,  or  that  perfectly  pure  alcohol  has 
a  density  of  0-794  at  60°,  we  mean  that  equal  bulks  of  these  two  liquids 
and  of  distilled  water  possess  weights  in  the  proportion  of  the  num- 
bers 1-85,  0-794,  and  1 ;  or  1850,  794,  and  1000.  It  is  necessary  to  be  par- 
ticular about  the  temperature ;  for,  as  will  be  hereafter  shown,  liquids  are 
extremely  expansible  by  heat ;  otherwise,  a  constant  bulk  of  the  same  liquid 
will  not  retain  a  constant  weight.  It  will  be  proper  to  begin  with  the  de- 
scription of  the  mode  in  which  the  specific  gravity  of  liquids  is  determined ; 
this  is  the  simplest  case,  and  the  one  which  best  illustrates  the  general 
principle. 

In  order  to  obtain  at  pleasure  the  specific  gravity  of  any  particular  liquid 
compared  with  that  of  water,  it  is  only  requisite  to  weigh  equal  bulks  at  the 
standard  temperature,  and  then  divide  the  weight  of  the  liquid  by  the  weight 
of  the  water ;  the  quotient  will  of  course  be  greater  or  less  than  unity,  as 
the  liquor  experimented  on  is  heavier  or  lighter  than  water.  Now,  to  weigh 
equal  bulks  of  two  fluids,  the  simplest  and  best  method  is  clearly  to  weigh 
them  in  succession  in  the  same  vessel,  taking  care  that  it  is  equally  full  on 
both  occasions,  a  condition  very  easy  of  fulfilment. 

A  thin  glass  bottle,  or  flask,  with  a  narrow  neck,  is  procured,  of  the  figure 
represented  on  the  next  page,  (fig.  1),  and  of  such  capacity  as  to  contain, 
when  filled  to  about  half-way  up  the  neck,  exactly  1000  grains  of  distilled 
water  at  60°  (15° -50).  Such  a  flask  is  readily  procured  from  any  one  of  the 
Italian  artificers,  to  be  foimd  in  every  large  town,  who  manufacture  cheap 
thermometers  for  sale.     A  counterpoise  of  the  exact  weight  of  the  empty 

*  In  other  words,  density  means  comparative  mass,  and  specific  gravity  comparative  weight. 
These  expressions,  although  really  relating  to  distinct  things,  axe  often  used  quite  indiffe- 
rently in  chemical  writings,  and  without  practical  inconvenience,  fiince  maae  and  weight  are 
d'rectly  proportional  to  each  other. 

(27) 


28 


DENSITY    AND    SPECIFIC    GRAVITY. 


Fig.  1. 


bottle  is  made  from  a  bit  of  brass,  an  old  weight, 
or  something  of  the  kind,  and  carefully  adjusted 
by  filing :  an  easy  task.  The  bottle  is  then  grad- 
uated, by  introducing  water  at  60°,  until  it  ex- 
actly balances  the  1000-grain  weight  and  counter- 
poise in  the  opposite  scale ;  the  height  at  which 
the  water  stands  in  the  neck  is  marked  by  a 
scratch,  and  the  instrument  is  complete  for  use. 
The  liquid  to  be  examined  is  brought  to  the  tem- 
perature of  60°,  and  with  it  the  bottle  is  filled  up 
to  the  mark  before  mentioned  ;  it  is  then  weighed, 
the  counterpoise  being  used  as  before,  and  the 
specific  gravity  directly  ascertained. 

A  watery  liquid  in  a  narrow  glass  tube  always 
presents  a  curved  surface  from  the  molecular  ac- 
tion of  the  glass,  the  concavity  being  upwards.    It 
is  better,  on  this  account,  in  graduating  the  bottle, 
to  make  two  scratches  as  represented  in  the  draw- 
ing, one  at  the  top  and  the  other  at  the  bottom  of 
the  curve :  this  prevents  any  future  mistake.    The 
marks  are  easily  made  by  a  fine,  sharp,  three-square  file,  the  hard  point  of 
\»hich,  also,  it  may  be  observed,  answers  perfectly  well  for  writing  upon 
glass,  in  the  absence  of  a  proper  diamond-pencil. 

The  specific-gravity  bottle  above  described  difi'ers  from  those  commonly 
made  for  sale  by  the  instrument-makers.  These  latter  are  constructed  with 
a  perforated  stopper,  so  arranged  that  when  the  bottle  is  quite  filled,  the 
stopper  put  in  its  place,  and  the  excess  of  liquid  which  flows  through  the 
hole  wiped  from  the  outside,  a  constant  measure  is  always  had.  There  are 
inconveniences  attending  the  use  of  the  stopper  which  lead  to  a  preference 
of  the  open  bottle  with  merely  a  mark  on  the  neck,  even  when  very  volatile 
liquids  are  experimented  with. 

It  will  be  quite  obvious  that  the  adoption  of  a  flask  holding  exactly  1000 
grains  of  water  has  no  other  object  than  to  save  the  trouble  of  a  very  trifling 
calculation ;  any  other  quantity  would  answer  just  as  well,  and,  in  fact,  the 
experimental  chemist  is  often  compelled  to  use  a  bottle  of  much  smaller  di- 
mensions, from  scarcity  of  the  liquid  to  be  examined.  The  shape  is  also  in 
reality  of  little  moment ;  any  light  phial  with  a  narrow  neck  may  be  em- 
ployed, not  quite  so  conveniently  perhaps,  as  a  specific-gravity  bottle. 

The  determination  of  the  specific  gravity  of  a  solid  is  also  an  operation  of 

great  facUity,  although  the  principle  is  not  so  obvious.     As  it  would  be 

impossible  to  put  in  practice  a  direct  method  like  that  indicated  for  liquids, 

recourse  is  had  to  another  plan.     The  celebrated  theorem  of  Archimedes 

affords  a  solution  of  the  difficulty.     This  theorem  may  be  thus  expressed : — 

When  a  solid  is  immersed  in  a  fluid,  it  loses  a  portion  of  its  weight ; 

and  this  portion  is  equal  to  the  weight  of  the  fluid  which  it  displaces ; 

that  is,  to  the  weight  of  its  own  bulk  of  that  fluid. 

It  is  easy  to  give  experimental  proof  of  this  very  important  proposition, 

as  well  as  to  establish  it  by  reasoning.     The  drawing  (fig.  2)  represents  a 

little  apparatus  for  the  former  purpose.     This  consists  of  a  thin  cylindrical 

vessel  of  brass,  into  the  interior  of  which  fits  very  accurately  a  solid  cylinder 

of  the  same  metal,  thus  exactly  filling  it.     When  the  cylinder  is  suspendeu 

beneath  the  bucket,  as  seen  in  the  sketch,  the  whole  hung  from  the  arm  of 

a  balance  and  counterpoised,  and  then  the  cylinder  itself  immersed  in  water, 

it  will  be  found  to  have  lost  a  certain  weight ;  and  that  this  loss  is  precisely 

equal  to  the  weight  of  an  equal  bulk  of  water,  may  then  be  proved  by  filling 


DENSITY    AND    SPECIFIC    GRAVITY, 


29 


tie  bucket  to  the  brim,  whereupon  the  equilibrium 
ffill  be  restored. 

The  consideration  of  the  great  hydrostatic  law  of 
fluid  pressure  easily  proves  the  truth  of  the  principle 
laid  down.  Let  the  reader  figure  to  himself  a  vessel 
of  water,  having  immersed  in  it  a  solid  cylindrical  or 
rectangular  body,  and  so  adjusted  with  respect  to 
density,  that  it  shall  float  indifferently  in  any  part 
beneath  the  surface  (fig.  3). 

Now  the  law  of  fluid  pressure  is  to  this  effect : — 
The  pressure  exerted  by  a  fluid  upon  the  containing 
vessel,  or  upon  anything  plunged  beneath  its  surface, 
depends,  first,  upon  the  density  of  that  fluid,  and, 
secondly,  upon  the  perpendicular  height  of  the  col- 
umn. It  is  independent  of  the  form  and  .lateral 
dimensions  of  the  vessel  or  immersed  body.  More- 
over, owing  to  the  peculiar  physical  constitution  of 
fluids,  this  pressure  is  exerted  equally  in  every  di- 
rection, upwards,  downwards,  and  laterally,  with 
equal  force. 

The  floating  body  is  in  a  state  of  equilibrium; 
therefore  the  pressure  downwards  caused  by  its  gravi- 
tation must  be  exactly  compensated  by  the  upward 
transmitted  pressure  of  the  column  of  water  a,  b. 

But  this  pressure  downwards  is  obviously  equal  to 
the  weight  of  an  equal  quantity  of  water,  since  the 
body  of  necessity  displaces  its  own  bulk — 

Hence,  the  weight  lost,  or  supported  by  the  water, 
is  the  weight  of  a  volume  of  water  equal  to  that  of 
the  body  immersed. 

Whatever  be  the  density  of  the  substance  it  will  be 
buoyed  up  to  this  amount;  in  the  case  supposed, 
the  buoyancy  is  equal  to  the  whole  weight  of  the 
body,  which  is  thus,  while  in  the  water,  reduced  to 
nothing. 

A  little  reflection  will  show  that  the  same  reasoning 
may  be  applied  to  a  body  of  irregular  form ;  besides, 
a  solid  of  any  figure  may  be  divided  by  the  imagina- 
tion, into  a  multitude  of  little  perpendicular  prisms, 
or  cylinders,  to  each  of  which  the  argument  may  be 
applied.  What  is  true  of  each  individually,  must 
necessarily  be  true  of  the  whole  together. 

This  is  the  fundamental  principle ;  its  application 
is  made  in  the  following  manner : — Let  it  be  required, 
for  example,  to  know  the  specific  gravity  of- a  body 
of  extremely  irregular  form,  as  a  small  group  of  rock- 
crystals  :  the  first  part  of  the  operation  consists  in 
determining  its  absolute  weight,  or,  more  correctly 
speaking,  its  weight  in  air ;  it  is  next  suspended  from 
the  balance-pan  by  a  fine  horse-hair,  immersed  com- 
pletely (fig.  4)  in  pure  water  at  60°  (15°-5C),  and 
again  weighed.  It  now  weighs  less,  the  difference 
being  the  weight  of  the  water  it  displaces,  that  is,  the 
weight  of  an  equal  bulk.  This  being  known,  nothing 
more  is  required  than  to  find,  by  division,  how  many 
3* 


Fig.  2. 


Fig.  3. 


30  DENSITY    AND    SPECIFIC    GRAVITY. 

times  the  latter  number  is  contained  in  the  former;  the  quotient  will  be  the 
density,  water  being  taken  =  1.     For  example : — 

The  quartz-crystals  weigh  in  air 293-7  grains. 

When  immersed  in  water,  they  weigh 180-1 

Difference  being  the  weight  of  an  equal  volume  of  water  ...  113-6 
293-7 
-■-■o.g  =  2-58,  the  specific  gravity  required. 

The  arbitrary  rule  is  generally  thus  written :  "Divide  the  weight  in  air 

by  the  loss  of  weight  in  water,  and  the  quotient  will  be  the  specific  gravity. " 

In  reality,  it  is  not  the  weight  in  air  which  is  required,  but  the  weight  the 

body  would   have  in  empty  space :    the  error  introduced, 

Fig.  5.  namely,  the  weight  of  an  equal  bulk  of  air,  is  so  trifling  that 

it  is  usually  neglected. 

Sometimes  the  body  to  be  examined  is  lighter  than  water, 
and  floats.  In  this  case  it  is  first  weighed  and  afterwards 
attached  to  a  piece  of  metal  (fig.  5),  heavy  enough  to  sink 
it,  and  suspended  from  the  balance.  The  whole  is  then  ex- 
actly weighed,  immersed  in  water,  and  again  weighed.  The 
difterence  between  the  two  weighings  gives  the  weight  of  a 
quantity  of  water  equal  in  bulk  to  both  together.  The  light 
substance  is  then  detached,  and  the  same  operation  of  weigh- 
ing in  air,  and  again  in  water,  repeated  on  the  piece  of  metal. 
These  data  give  the  means  of  finding  the  specific  gravity,  as 
will  be  at  once  seen  by  the  following  example : — 

Light  substance  (a  piece  of  wax)  weighs  in  air 133-7  grains. 

Attached  to  a  piece  of  brass,  the  whole  now  weighs 183-7 

Immersed  in  water,  the  system  weighs  38-8 

Weight  of  water  equal  in  bulk  to  brass  and  wax  144-9 

Weight  of  brass  in  air 60-0 

Weight  of  brass  in  water  44-4 

Weight  of  equal  bulk  of  water 5-6 

Bulk  of  water  equal  to  wax  and  brass  144-9 

Bulk  of  water  equal  to  brass  alone 5-6 

Bulk  of  water  equal  to  wax  alone  , 139-3 

133-7 

139-3  —  ^•9^^8- 

In  all  such  experiments,  it  is  necessary  to  pay  attention  to  the  temperature 
and  purity  of  the  water,  and  to  remove  with  great  care  all  adhering  air- 
bubbles  ;  otherwise  a  false  result  will  be  obtained. 

Other  cases  require  mention  in  which  these  operations  must  be  modified 
to  meet  particular  diflBculties.  One  of  these  happens  when  the  substance  is 
dissolved  or  acted  upon  by  water.  This  difficulty  is  easily  conquered  by 
substituting  some  other  liquid  of  known  density  which  experience  shows  is 
without  action.  Alcohol  or  oil  of  turpentine  may  generally  be  used  when 
water  is  inadmissible.  Suppose,  for  instance,  the  specific  gravity  of  crys- 
tallized sugar  is  required,  we  proceed  in  the  following  way : — The  specific 
gravity  of  the  oil  of  turpentine  is  first  carefully  determined  ;  let  it  be  0-87 ; 


DENSITY    AND    SPECIFIC   GRAVITY.  81 

the  sugar  is  next  weighed  in  the  air,  then  suspended  by  a  horse-hair,  and 
weighed  in  the  oil ;  the  difference  is  the  weight  of  an  equal  bulk  of  the  latter ; 
a  simple  calculation  gives  the  weight  of  a  corresponding  volume  of  water : — 

Weight  of  sugar  in  air 400     grains. 

Weight  of  sugar  in  oil  of  turpentine 182-5 

Weight  of  equal  bulk  of  oil  of  turpentine  217-5 

87  :  100  =  217-5  :  250, 
the  weight  of  an  equal  bulk  of  water ;  hence  the  specific  gravity  of  the  sugar, 

!1«  =  1.6. 
250 

The  substance  to  be  examined  may  be  in  small  fragments,  or  powder. 
Here  the  operation  is  also  very  simple.  A  bottle  holding  a  known  weight 
of  water  is  taken ;  the  specific-gravity  bottle  already  described  answers  per- 
fectly well.  A  convenient  quantity  of  the  substance  is  next  carefully  weighed 
out,  and  introduced  into  the  bottle,  which  is  then  filled  up  to  the  mark  on 
the  neck  with  distilled  water.  It  is  clear  that  the  vessel  now  contains  less 
water  by  a  quantity  equal  to  the  bulk  of  the  powder  than  if  it  were  filled  in 
the  usual  manner.  It  is,  lastly,  weighed.  In  the  subjoined  experiment 
emery  powder  was  tried. 

The  bottle  held,  of  water   1000  grains. 

The  substance  introduced  weighed 100 

Weight  of  the  whole,  had  no  water  been  displaced  1100 

The  observed  weight  is,  however,  only  1070 

Hence  water  displaced,  equal  in  bulk  to  the  powder  30 

100 

QQ-  =  3-333  specific  gravity. 

By  this  method  the  specific  gravities  of  metals  in  powder,  metallic  oxides, 
and  other  compounds,  and  salts  of  all  descriptions,  may  be  determined  with 
great  ease.  Oil  of  turpentine  may  be  used  with  most  soluble  salts.  The 
crystals  should  be  crushed  or  roughly  powdered  to  avoid  errors  arising  from 
cavities  in  their  substance. 

The  theorem  of  Archimedes  affords  the  key  to  the  general  doctrine  of  the 
equilibrium  of  floating  bodies,  of  which  an  application  is  made  in  the  common 
hydrometer, — an  instrument  for  finding  the  specific  gravities  of  liquids  in  a 
very  easy  and  expeditious  manner. 

When  a  solid  body  is  placed  upon  the  surface  of  a  fluid  specifically  heavier 
than  itself,  it  sinks  down  until  it  displaces  a  quantity  of  fluid  equal  to  its 
own  weight,  at  which  point  it  floats.  Thus,  in  the  case  of  a  substance  floating 
in  water,  whose  specific  weight  is  one-half  that  of  the  fluid,  the  position  of 
equilibrium  will  involve  the  immersion  of  exactly  one-half  of 
the  body,  inasmuch  as  its  whole  weight  is  counterpoised  by  a  ^^S-  6. 

quantity  of  water  equal  to  half  its  volume.     If  the  same  body 
were  put  into  a  fluid  of  one-half  the  specific  gravity  of  water,      /  p«^ 
if  such  could  be  found,  then  it  would  sink  beneath  the  surface,      ' 
and  remain  indifferently  in  any  part.  A  floating  body  of  known 
specific  gravity  may  thus  be  used  as  an  indicator  of  the  spe-         '\|| 
cific  gravity  of  a  fluid.    In  this  manner  little  glass  beads  (fig.  6)  ff^  ' 

of  known  specific  gravities  are  sometimes  employed  in  the  arts 
to  ascertain  in  a  rude  manner  the  specific  gravity  of  liquids  ; 


32 


DENSITY    AND    SPECIFIC    GRAVITY. 


Fig.  7. 


the  one  that  floats  indifl'erently  beneath  the  surface,  -without  either  sinking 
or  rising,  has  of  course  the  same  specific  gravity  as  the  liquid  itself;  this  is 
pointed  out  by  the  number  marked  upon  the  bead. 

The  hydrometer  (fig.  7)  in  general  use  consists 
of  a  floating  vessel  of  thin  metal  or  glass,  having 
a  weight  beneath  to  maintain  it  in  an  upright 
position,  and  a  stem  above  bearing  a  divided 
scale.  The  use  of  the  instrument  is  very  simple. 
The  liquid  to  be  tried  is  put  into  a  small  narrow 
jar,  and  the  instrument  floated  in  it.  It  is  obvious 
that  the  denser  the  liquid,  the  higher  will  the 
hydrometer  float,  because  a  smaller  displacement 
of  fluid  will  counterbalance  its  weight.  For  the 
same  reason,  in  a  liquid  of  less  density,  it  sinks 
deeper.  The  hydrometer  comes  to  rest  almost 
immediately,  and  then  the  mark  on  the  stem  at  the 
fluid-level  may  be  read  off". 

Very  extensive  use  is  made  of  instruments  of 
this  kind  in  the  arts ;  these  sometimes  bear  dif- 
ferent names,  according  to  the  kind  of  liquid  for 
which  they  are  intended ;  but  the  principle  is  the 
same  in  all.  The  graduation  is  very  commonly 
arbitrary,  two  or  three  difi'erent  scales  being  un- 
fortunately used.  These  may  be  sometimes  re- 
duced, however,  to  the  true  numbers  expressing 
the  specific  gravity  by  the  aid  of  tables  of  com- 
parison drawn  up  for  the  purpose. 

A  very  convenient  and  useful  instrument  in  the 
shape  of  a  small  hydrometer  (fig.  8)  for  taking  the 
specific  gravity  of  urine,  has  lately  been  put  into 
the  hands  of  the  physician  ;'  it  may  be  packed  into 
a  pocket-case,  with  a  little  jar  and  a  thermometer, 
and  is  always  ready  for  use.* 

The  determination  of  the  specific  gravity  of 
gases  and  vapours  of  volatile  liquids  is  a  problem 
of  very  great  practical  importance  to  the  chemist ; 
the  theory  of  the  operation  is  as  simple  as  when 
liquids  themselves  are  concerned,  but  the  pro- 
cesses are  much  more  delicate,  and  involve  be- 
sides certain  corrections  for  difi^erences  of  tem- 
perature and  pressure,  founded  on  principles  yet 
to  be  discussed.  It  will  be  proper  to  defer  the 
consideration  of  these  matters  for  the  present. 
The  method  of  determining  the  specific  gravity 
of  a  gas  will  be  found  described  under  the  head  of 


Fig.  8. 


'  This  and  other  instruments  described  or  figured  in  the  course  of  the  work,  may  be  had 
of  rtr.  Newman,  122  Regent  Street,  upon  the  excellence  of  whose  workmanship  reliance  may 
be  safely  placed. 

*  The  graduation  of  the  urinometer  is  such  that  each  degree  represents  1-1000,  thus 
giving  the  actual  specific  gravity  without  calculation,  for  the  number  of  degrees  on  the 
scale  cut  by  the  surface  of  the  liquid  when  this  instrument  is  at  rest,  added  to  1000  will 
epresent  the  density  of  the  liquid.  If,  for  example,  the  surface  of  the  liquid  coincide  with 
•23  on  the  scale,  the  specific  gravity  will  be  1023,  about"  the  average  density  of  healthy 
urine. — &  B. 


DENSITY    AND    SPECIFIC    GRAVITY. 


33 


•♦  Ojcygen,"  and  that  of  the  vapour  of  a  volatile  liquid  in  the  Introduction 
to  Organic  Chemistry/ 


*  The  mode  of  determining  the  specific  gravity  of  a  liquid  by  means  of  a 
solid  has  been  omitted  in  the  text.  It  results  from  the  theorem  of  Ar- 
chimedes, that  if  any  solid  be  immersed  in  water  and  then  in  any  other 
liquid,  the  loss  of  veight  sustained  in  each  case  will  give  the  relative 
weights  of  equal  hulks  of  the  liquids,  and  on  dividing  the  weight  of  the 
liquid  by  the  weight  of  the  water,  the  quotient  will  be  the  specific  gravity 
of  the  liquid  experimented  on.  For  instance,  let  a  piece  of  glass  rod  be 
suspended  from  the  balance-pan  and  exactly  counterpoised,  then  immerse 
it  in  water  and  restore  the  equipoise  by  weights  added  to  the  pan  to 
which  the  glass  is  suspended,  the  amount  will  give  the  loss  of  weight  by 
immersion  or  the  weight  of  a  bulk  of  water  equal  to  that  of  the  rod. 
Now  wipe  the  glass  dry,  and  having  removed  the  additional  weights, 
immerse  it  in  the  other  liquid,  and  restore  the  equipoise  as  before,  ">L!s 
latter  weight  is  the  weight  of  a  bulk  of  the  liquid  equal  to  that  of  the 
water.  The  latter  divided  by  the  former  gives  the  specific  gravity,  jfo* 
example : — 

The  glass  rod  loses  by  immersion  in  water 171  f*  *«•«. 

The  glass  rod  loses  by  immersion  in  alcohol 143 

—  =.•836  the  specific  gravity  required.  —  R.  B. 


Fig.  9. 


m 


PHYSICAL    CONSTITUTION 


OF  THE  PHYSICAL  CONSTITUTION  OP  THE  ATMOSPHERE,  AND 
OF  GASES  IN  GENERAL. 


Fig.  10. 


It  requires  some  little  abstraction  of  mind  to  realize  completely  the  singu- 
lar condition  in  which  all  things  at  the  surface  of  the  earth  exist.  We  live 
at  the  bottom  of  an  immense  ocean  of  gaseous  matter,  which  envelopes 
everything,  and  presses  upon  everything  with  a  force  which  appears,  at  first 
sight,  perfectly  incredible,  but  whose  actual  amount  admits  of  easy  proof. 

Gravity  being,  so  far  as  is  known,  common  to  all  matter,  it  is  natural  to 
expect  that  gases,  being  material  substances,  should  be  acted  upon  by  the 
earth's  attraction,  as  well  as  solids  and  liquids.  This  is  really  the  case,  and 
the  result  is  the  weight  or  pressure  of  the  atmosphere,  which  is  nothing 
more  than  the  effect  of  the  attraction  of  the  earth  on  the  particles  of  air. 

Before  describing  the  leading  phenomena  of  the  atmospheric  pressure,  it 
is  necessary  to  notice  one  very  remarkable  feature  in  the  physical  constitu- 
tion of  gases,  upon  which  depends  the  principle  of  an  extremely  valuable 
instrument,  the  air-pump. 

Gases  are  in  the  highest  degree  elastic  ;  the  volume  or  space  which  a  gas 
occupies  depends  upon  the  pressure  exerted  upon  it.  Let  the  reader  imagine 
a  cylinder,  a,  fig.  10,  closed  at  the  bottom,  in 
which  moves  a  piston,  air-tight,  so  that  no  air 
can  escape  between  the  piston  and  the  cylinder. 
Suppose  now  the  piston  be  pressed  downwards 
with  a  certain  force ;  the  air  beneath  it  will  be 
compressed  into  a  smaller  bulk,  the  amount  of 
this  compression  depending  on  the  force  ap- 
plied ;  if  the  power  be  sufficient,  the  bulk  of 
the  gas  may  be  thus  diminished  to  one  hun- 
dredth part  or  less.  When  the  pressure  is  re- 
moved, the  elasticity  or  tension,  as  it  is  called, 
of  the  included  air  or  gas,  will  immediately 
force  up  the  piston  until  it  arrives  at  its  first 
position. 

Again,  take  b,  fig.  10,  and  suppose  the  piston  to 
stand  about  the  middle  of  the  cylinder,  having 
air  beneath  in  its  usual  state.  If  the  piston 
be  now  drawn  upwards,  the  air  below  will  ex- 
pand, so  as  to  fill  completely  the  enclosed 
space,  and  this  to  an  apparently  unlimited  ex- 
tent. A  volume  of  air  which  under  ordinary  circumstances  occupies  the 
bulk  of  a  cubic  inch,  might,  by  the  removal  of  the  pressure  upon  it,  be 
made  to  expand  to  the  capacity  of  a  whole  room,  while  a  renewal  of  the 
former  pressure  would  be  attended  by  a  shrinking  down  of  the  air  to  its 
former  bulk.  The  smallest  portion  of  gas  introduced  into  a  large  exhausted 
vessel  becomes  at  once  diffused  through  the  whole  space,  an  equal  quantity 
being  present  in  every  part;  the  vessel  is  full,  although  the  gas  is  in  a  state 
of  extreme  tenuity.  This  power  of  expansion  which  air  possesses  may  have, 
and  probably  has,  in  reality,  a  limit;  but  the  limit  is  never  reached  in 


OF    THE    ATMOSPHERE. 


35 


practice.  Wc  are  quite  safe  in  the  assumption,  that,  for  ail  purposes  of 
experiment,  however  refined,  air  is  perfectly  elastic. 

It  is  usual  to  assign  a  reason  for  this  indefinite  expansibility  by  ascribing 
to  the  particles  of  material  bodies,  when  in  a  gaseous  state,  a  self-repulsive 
energy.  This  statement  is  commonly  made  somewhat  in  this  manner: 
matter  is  under  the  influence  of  tw^o  opposite  forces,  one  of  which  tends  to 
draw  the  particles  together,  the  other  to  separate  them.  By  the  preponde- 
rance of  one  or  other  of  these  forces,  we  have  the  three  states  called  solid, 
liquid,  and  gaseous.  When  the  particles  of  matter,  in  consequence  of  the 
direction  and  strength  of  their  mutual  attractions,  possess  only  a  very  slight 
power  of  motion,  a  solid  substance  results ;  when  the  forces  are  nearly 
balanced,  we  have  a  liquid,  the  particles  of  which  in  the  interior  of  the 
mass  are  free  to  move,  but  yet  to  a  certain  extent  are  held  together ;  and, 
lastly,  when  the  attractive  power  seems  to  be  completely  overcome  by  its 
antagonist,  we  have  a  gas  or  vapour. 

Various  names  are  applied  to  these  forces,  and  various  ideas  entertained 
concerning  them  ;  the  attractive  forces  bear  the  name  of  cohesion  when  they 
are  exerted  between  particles  of  matter  separated  by  a  very  small  interval, 
and  gravitation,  when  the  distance  is  great.  The  repulsive  principle  is  often 
thought  to  be  identical  with  the  principle  of  heat. 

Fig.  11. 


The  ordinary  air-pump,  shown  in  section  in  fig.  11,  consists  essentially  of 
A  metal  cylinder,  in  which  moves  a  tightly-fitting  piston,  by  the  aid  of  its 
rod.  The  bottom  of  the  cylinder  communicates  with  the  vessel  to  be  ex- 
hausted, and  is  furnished  with  a  valve  opening  upwards.  A  similar  valve, 
also  opening  upwards,  is  fitted  to  the  piston ;  these  valves  are  made  with 
slips  of  oiled  silk.  When  the  piston  is  raised  from  the  bottom  of  the  cy 
linder,  the  space  left  beneath  it  must  be  void  of  air,  since  the  piston-valve 
opens  only  in  one  direction ;  the  air  within  the  receiver  having  on  that  side 
nothing  to  oppose  its  elastic  power  but  the  weight  of  the  little  valve,  lifts 
the  latter,  and  escapes  into  the  cylinder.  So  soon  as  the  piston  begins  to 
descend,  the  lower  valve  closes,  by  its  own  weight,  or  by  the  transmitteel 
pressure  from  above,  and  communication  with  the  receiver  is  cut  oflF.  As 
the  descent  of  the  piston  continues,  the  air  included  within  the  cylinder  be- 


36 


PHYSICAL    CONSTITUTION 


comes  compressed,  its  elasticity  is  increased,  and  at  length  it  forces  opep 
the  upper  valve,  and  escapes  into  the  atmosphere.  In  this  manner,  a  cy- 
linder full  of  air  is  at  every  stroke  of  the  pump  removed  from  the  receiver. 
During  the  descent  of  the  piston,  the  upper  valve  remains  open,  and  the 
lower  closed,  and  the  reverse  during  the  opposite  movement. 


Pig.  12. 


In  practice,  it  is  very  convenient  to  have  two  such  barrels  or  cylinders, 
arranged  side  by  side,  the  piston-rods  of  which  are  formed 
■""ig.  18.  into  racks,  having  a  pinion,  or  small-toothed  wheel,  be- 

tween them,  moved  by  a  winch.  By  this  contrivance  the 
operation  of  exhaustion  is  much  facilitated  and  the  labour 
lessened.     The  arrangement  is  shown  in  fig.  12. 

A  simpler  and  far  superior  form  of  air-pump  is  thus 
constructed:  the  cylinder,  which  may  be  of  large  dimen- 
sions, is  furnished  with  an  accurately-fitted  solid  piston, 
the  rod  of  which  moves,  air-tight,  through  a  contrivance 
called  a  stufiing-box,  at  the  top  of  the  cylinder,  where  also 
the  only  valve  essential  to  the  apparatus  is  to  be  found ;  the 
latter  is  a  solid  conical  plug  of  metal,  shown  at  a  in  the 
figure,  kept  tight  by  the  oil  contained  in  the  chamber  into 
which  it  opens.  The  communication  with  the  vessel  to  be 
exhausted  is  made  by  a  tube  which  enters  the  cylinder  a 
little  above  the  bottom.  The  action  is  the  following :  let 
the  piston  be  supposed  in  the  act  of  rising  from  the  bottom 
of  the  cylinder ;  as  soon  as  it  passes  the  mouth  of  the  tube 
t,  all  communication  is  stopped  between  the  air  above  the 
piston  and  the  vessel  to  be  exhausted ;  the  enclosed  air 
"'^  sufi"ers  compression,  until  it  acquires  sufficient  elasticity 
to  lift  the  metal  valve  and  escape  by  bubbling  through  the 
oil.     When  the  piston  makes  its  descent,  and  this  valve 


OP    THE    ATMOSPHERE. 


87 


Fig.  14. 


closes,  a  vacuum  is  left  in  the  upper  part  of  the  cylinder,  into  which  the  air 
of  the  receiver  rushes  so  soon  as  the  piston  has  passed  below  the  orifice  of 
the  connecting  tube. 

In  the  silk-valved  air-pump,  exhaustion  ceases  when  the  elasticity  of  the 
air  in  the  receiver  becomes  toe  feeble  to  raise  the  valve ;  in  that  last 
described,  the  exhaustion  may,  on  the  contrary,  be  carried  to  an  indefinite 
extent,  without,  however,  under  the  most  favourable  circumstances,  be- 
coming complete.  The  conical  valve  is  made  to  project  a  little  below  the 
cover  of  the  cylinder,  so  as  to  be  forced  up  by  the  piston  when  the  latter 
reaches  the  top  of  the  cylinder ;  the  oil  then  enters  and  displaces  any  air 
that  may  be  lurking  in  the  cavity. 

It  is  a  great  improvement  to  the  machine  to  supply  the  piston  with  a 
relief-valve  opening  upwards ;  this  may 
also  be  of  metal,  and  contained  within  the 
body  of  the  piston.  Its  use  is  to  avoid 
the  momentary  condensation  of  the  air  in 
the  receiver  when  the  piston  descends. 
The  pump  is  worked  by  a  lever  in  the 
manner  represented  in  fig.  14. 

To  return  to  the  atmosphere.  Air  pos- 
sesses weight :  a  light  flask  or  globe  of 
glass,  furnished  with  a  stop-cock  and  ex- 
hausted by  the  air-pump,  weighs  consi- 
derably less  than  when  full  of  air.  If  the 
capacity  of  the  vessel  be  equal  to  100 
cubic  inches,  this  difference  may  amount 
to  nearly  30  grains. 

The  mere  fact  of  the  pressure  of  the 
atmosphere  may  be  demonstrated  by  se- 
curely tying  a  piece  of  bladder  over  the 
mouth  of  an  open  glass  receiver,  and  then 
exhausting  the  air  from  beneath  it ;  the 
bladder  will  become  more  and  more  con- 
cave, tmtil  it  suddenly  breaks.  A  thin 
square  glass  bottle,  or  a  large  air-tight 
tin  box,  may  be  crushed  by  withdrawing 
the  support  of  the  air  in  the  inside. 
Steam-boilers  have  been  often  destroyed 
in  this  manner  by  collapse,  in  conse- 
quence of  the  accidental  formation  of  a 
partial  vacuum  within. 

After  what  has  been  said  on  the  subject 
of  fluid  pressure,  it  will  scarcely  be  ne- 
cessary to  observe  that  the  law  of  equality 
of  pressure  in  all  directions  also  holds 
good  in  the  case  of  the  atmosphere.  The 
perfect  mobility  of  the  particles  of  air 
permits  the  transmission  of  the  force  ge- 
nerated by  their  gravity.  The  sides  and 
bottom  of  an  exhausted  vessel  are  pressed 
upon  with  as  much  force  as  the  top. 

If  a  glass  tube  of  considerable  length 
could  be  perfectly  exhausted  of  air,  and 
then  held  in  an  upright  position,  with  one 
of  its  ends  dipping  into  a  vessel  of  liquid, 


88 


PHYSICAL    CONSTITUTION 


Fig  .15.  the  latter,  on  being  allowed  access  to  the  tube,  would  rise  in 
its  interior  until  the  weight  of  the  column  balanced  the  pres- 
sure of  the  air  upon  the  surface  of  the  liquid.  Now  if  the 
density  of  this  liquid  were  known,  and  the  height  and  area 
of  the  column  measureji,  means  would  be  furnished  for  ex- 
actly estimating  the  amount  of  pressure  exerted  by  the  atmo- 
sphere. Such  an  instrument  is  the  barometer:  a  straight 
glass  tube  is  taken,  about  36  inches  in  length,  and  sealed  bj 
the  blow-pipe  flame  at  one  extremity ;  it  is  then  filled  with 
clean,  dry  mercury,  care  being  taken  to  displace  all  air- 
bubbles,  the  open  end  stopped  with  a  finger,  and  the  tube  in- 
verted in  a  basin  of  mercury.  On  removing  the  finger,  the 
fluid  sinks  away  from  the  top  of  the  tube,  until  it  stands  at 
the  height  of  about  30  inches  above  the  level  of  that  in  the 
basin.  Here  it  remains  supported  by,  and  balancing  the  at- 
mospheric pressure,  the  space  above  the  mercury  in  the  tube 
being  of  necessity  empty. 

The  pressure  of  the  atmosphere  is  thus  seen  to  be  capable 
of  sustaining  a  column  of  mercury  30  inches  in  height,  or 
thereabouts ;  now  such  a  column,  having  an  area  of  one  inch, 
weighs  between  14  and  15  pounds,  consequently  such  must 
be  the  amount  of  the  pressure  exerted  upon  every  square 
inch  of  the  surface  of  the  earth,  and  of  the  objects  situated 
thereon,  at  least  near  the  level  of  the  sea.  This  enormous 
force  is  borne  without  inconvenience  by  the  animal  frame,  by 
reason  of  its  perfect  uniformity  in  every  direction,  and  it  may 
be  doubled,  or  even  tripled  without  injury. 

A  barometer  may  be  constructed  with  other  liquids  besides 
mercury ;  but,  as  the  height  of  the  column  must  always  bear 
an  inverse  proportion  to  the  density  of  the  liquid,  the  length 
of  tube  required  will  be  often  considerable ;  in  the  case  of 
water  it  will  exceed  33  feet.  It  is  seldom  that  any  other 
liquid  than  mercury  is  employed  in  the  construction  of  this 
instrument.  The  Royal  Society  of  London  possess  a  water- 
barometer  at  their  apartments  at  Somerset  House.  Its  con- 
struction was  attended  with  great  difficulties,  and  it  has  been  found  impos- 
sible to  keep  it  in  repair.  / 

It  will  now  be  necessary  to  consider  a  most  important  law  which  connects 
the  volume  occupied  by  a  gas  with  the  pressure  made  upon  it,  and  which  is 
thus  expressed :  — 

The  volume  of  a  gas  is  inversdy  as  the  pressure ;  the  density  and  elastic 
force  are  directly  as  the  pressure,  and  inversely  a«  the  volume. 
For  instance,  100  cubic  inches  of  gas  under  a  pressure  of  30  inches  of 
mercury  would  expand  to  200  cubic  inches  were  the  pressure  reduced  to 
one-half,  and  shrink,  on  the  contrary,  to  50  cubic  inches  if  the  original  pres- 
sure were  doubled.  The  change  of  density  must  necessarily  be  in  the 
inverse  proportion  to  that  of  the  volume,  and  the  elastic  force  follows  the 
same  rule. 

This,  which  is  usually  called  the  law  of  Marietta,  is  easily  demonstrable 
by  direct  experiment.  A  glass  tube,  about  7  feet  in  length,  is  closed  at  one  end, 
and  bent  into  the  form  shown  in  fig.  16,  the  open  limb  of  the  siphon  being 
the  longest.  It  is  next  attached  to  a  board  furnished  with  a  moveable  scale 
of  inches,  and  enough  mercury  is  introduced  to  fill  the  bend,  the  level  being 
evenly  adjusted,  and  marked  upon  the  board.  Mercury  is  now  poured  into 
the  tube  until  it  is  found  that  thp  inclosed  air  has  been  reduced  to  one-half 
of  its  former  volume ;  and  on  applying  the  scale  it  will  be  found  that  the  level 


OF    THE    ATMOSPHERE 


39 


I 


bi  the  mercury  in  the  open  part  of  the  tube  stands  Fig.  16. 

very  nearly  30  inches  above  that  in  the  closed  portion. 
The  pressure  of  an  additional  "atmosphere"  has  con- 
sequently reduced  the  bulk  of  the  contained  air  to 
one-half.  If  the  experiment  be  still  continued  until 
the  volume  of  air  is  reduced  to  a  third,  it  will  be  found 
that  the  column  measures  60  inches,  and  so  in  like 
proportion  as  far  as  the  experiment  is  carried. 

The  above  instrument  is  better  adapted  for  illustra- 
tion of  the  principle  than  for  furnishing  rigorous  proof 
of  the  law;  this  has,  however,  been  done.  MM.  Arago 
and  Dulong  published,  in  the  year  1830,  an  account  of 
certain  experiments  made  by  them  in  Paris,  in  which 
the  law  in  question  had  been  verified  to  the  extent  of 
27  atmospheres. 

All  gases  are  alike  subject  to  this  law,  and  all  va- 
pours of  volatile  liquids,  when  remote  from  their  points 
of  liquefaction.'  It  is  a  matter  of  the  greatest  im- 
portance in  practical  chemistry,  since  it  gives  the 
means  of  making  corrections  for  pressure,  or  deter- 
mining by  calculation  the  change  of  volume  which  a  gas 
would  suffer  by  any  given  change  of  external  pressure. 

Let  it  be  required,  for  example,  to  solve  the  fol- 
lowing problem : — We  have  100  cubic  inches  of  gas  in 
a  graduated  jar,  the  barometer  standing  at  29  inches ; 
how  many  cubic  inches  will  it  occupy  when  the  column 
rises  to  30  inches  ? — Now  the  volume  must  be  inversely 
as  the  pressure ;  consequently  a  change  of  pressure  in 
the  proportion  of  29  to  30  must  be  accompanied  by 
a  change  of  volume  in  the  proportion  of  30  to  29  ;  30 
cubic  inches  of  gas  contracting  to  29  cubic  inches 
under  the  conditions  imagined.    Hence  the  answer : 

30  :  29  =  100  :  96-67  cubic  inches. 
The  reverse  of  the  operation  will  be   obvious.     The 
practical  pupil  will  do  well  to  familiarize  himself  with 
these  simple  calculations  of  correction  for  pressure. 

From  what  has  been  said  respecting  the  easy  com- 
pressibility of  gases,  it  will  be  at  once  seen  that  the 
atmosphere  cannot  have  the  same  density,  and  cannot 
exert  equal  pressures  at  different  elevations  above  the 
sea-level,  but  that,  on  the  contrary,  these  must  diminish 
with  the  altitude,  and  very  rapidly.  The  lower  strata 
of  air  have  to  bear  the  weight  of  those  above  them ; 

they  become,  in  consequence,  deeper  and  more  com-      f  .,^ ■'!H):i^ 

pressed  than  the  upper  portions.     The  following  table, 

which  is  taken  from  Prof.  Graham's  work,  shows  in  a  very  simple  manner 

the  rule  followed  in  this  respect. 

Height  above  the  _  Height  of  barometer, 


sea,  in  miles. 

0        

Volume  of  air. 
1 

in  inches. 
30 

2-705 

2  

5-41    

4  

8- 115 

8  

10-82    

16  

13-525 

32  

0-9375 

16-23    

fid  

ft./lAa7K 

*  When  near  the  liquefying  point  the  law  no  longer  holds;  the  volume  diminishes  m(/rt 
rapidly  than  the  theory  indicates,  a  smaller  amount  of  pressure  being  then  sufficient. 


40     PHYSICAL  CONSTITUTION   OP  THE  ATMOSPHERE. 


f 


I' 


Fig.  17.  The  numbers  in  the  first  column  form  an  arithmetical  series, 

by  the  constant  addition  of  2-705 ;  those  in  the  second  column  an 
increasing  geometrical  series,  each  being  the  double  of  its  prede- 
cessor ;  and  those  in  the  third,  a  decreasing  geometrical  series, 
in  which  each  number  is  the  half  of  that  standing  above  it.  In 
ascending  in  the  air  in  a  balloon,  these  effects  are  well  ob- 
served ;  the  expansion  of  the  gas  within  the  machine,  and  the 
fall  of  the  mercury  in  the  barometer,  soon  indicate  to  the  voya- 
ger the  fact  of  his  having  left  below  him  a  considerable  part  of 
the  whole  atmosphere. 

The  invention  of  the  barometer,  which  took  place  in  the  year 
1643,  by  Torricelli,  a  pupil  of  the  celebrated  Galileo,  speedily 
led  to  the  observation  that  the  atmospheric  pressure  at  the 
same  level  is  not  constant,  but  possesses,  on  the  contrary,  a 
small  range  of  variation,  seldom  exceeding  in  Europe  2  or  2-6 
inches,  and  within  the  tropics  usually  confined  within  much 
narrower  limits.  Two  kinds  of  variations  are  distinguished  ; 
regular  or  horary,  and  irregular  or  accidental.  It  has  been 
observed,  that  in  Europe  the  height  of  the  barometer  is  greatest 
at  two  periods  in  the  twenty-four  hours,  depending  upon  the 
season.  In  winter,  the  first  maximum  takes  place  about  9  a.  m., 
the  first  minimum  at  3  p.  m.,  after  which  the  mercury  again 
rises  and  attains  its  greatest  elevation  at  9  in  the  evening;  in 
summer  these  hours  of  the  aerial  tides  are  somewhat  altered. 
The  accidental  variations  are  much  greater  in  amount,  and 
render  it  extremely  difficult  to  trace  the  regular  changes  above 
mentioned. 

The  barometer  is  applied  vrith  great  advantage  to  the  mea- 
surement of  accessible  heights,  and  it  is  also  in  daily  use  for 
foretelling  the  state  of  the  weather ;  its  indications  are  in  this 
respect  extremely  deceptive,  except  in  the  case  of  sudden  and 
violent  storms,  which  are  almost  always  preceded  by  a  rapid 
fall  in  the  mercurial  column.  It  is  often  extremely  useful  in 
this  respect  at  sea. 

To  the  practical  chemist,  a  moderately  good  barometer  is  an 
indispensable  article,  since  in  all  experiments  in  which  volumes 
of  gases  are  to  be  estimated,  an  account  must  be  taken  of  the 
pressure  of  the  atmosphere.  The  marginal  drawing  represents 
a  very  convenient  and  economical  siphon  barometer  for  this 
purpose.  A  piece  of  new  and  stout  tube,  of  about  one-third  of 
an  inch  in  internal  diameter,  is  procured  at  the  glass-house, 
sealed  at  one  extremity,  and  bent  into  the  siphon  form,  as  repre- 
sented. Pure  and  warm  mercury  is  next  introduced  by  successive  portions 
until  the  tube  is  completely  filled,  and  the  latter  being  held  in  an  upright 
T)osition,  the  level  of  the  metal  in  the  lower  and  open  limb  is  conveniently 
adjusted  by  displacing  a  portion  by  a  stick  or  glass  rod.  The  barometer  is, 
lastly,  attached  to  a  board,  and  furnished  with  a  long  scale,  made  to  slide, 
which  may  be  of  box-wood,  with  a  slip  of  ivory  at  each  end.  When  an  ob- 
servation is  to  be  taken,  the  lower  extremity  or  zero  of  the  scale  is  placed 
exactly  even  with  the  mercury  in  the  short  limb,  and  then  the  height  of  the 
column  at  once  read  off. 


HEAT. 


41 


HEAT. 


It  will  be  convenient  to  consider  the  subject  of  Heat  under  several  sec- 
tions, and  in  the  following  order : — 

1.  Expansion  of  bodies,  or  effects  of  variations  of  temperature  in  altering 

their  dimensions. 

2.  Conduction,  or  transmission  of  heat. 

3.  Change  of  state. 

4.  Capacity  of  bodies  fop  heat. 

The  phenomena  of  radiation  must  be  deferred  until  a  sketch  has  been 
given  of  the  science  of  light. 

EXPANSION. 

If  a  bar  of  metal  (fig.  18)  be  taken,  of  such  magnitude  as  to  fit  accurately 
^0  a  gauge  when  cold,  heated  considerably,  and  again  applied  to  the  guage,  it 
will  be  found  to  have  become  enlarged  in  all  its  dimensions.  When  cold,  it 
will  once  more  enter  the  gauge. 

Again,  if  a  quantity  of  liquid  contained  in  a  glass  bulb  (fig.  19),  furnished 
with  a  narrow  neck,  be  plunged  into  hot  water,  or  exposed  to  any  other 


Fig.  18. 


I 


Fig.  19. 


Fig.  20. 


1= 


ft 


source  of  heat,  the  liquid  will  mount  in  the  stem,  showing  that  its  volume 
has  been  increased. 

Or,  if  a  portion  of  air  be  confined  in  any  vessel  (fig.  20),  the  application  of 
a  slight  degree  of  heat  will  suffice  to  make  it  occupy  a  space  sensibly  larger. 

This  most  general  of  all  the  effects  of  heat  furnishes  in  the  outset  a  prin- 
ciple, by  the  aid  of  which  an  instrument  can  be  constructed  capable  of  taking 
cognizance  of  changes  of  temperature  in  a  manner  equally  accurate  and  con- 
venient :  such  an  instrument  is  the  thermometer. 

A  capillary  glass  tube  is  chosen,  of  uniform  diameter  ■  one  extremity  is 
closed  and  expanded  into  a  bulb,  by  the  aid  of  the  \»lowpipe  flame,  and  the 
4  * 


42  HEAT. 

other  somewhat  drawn  out,  and  left  open.  The  bulb  is  now  cautiously  heated 
by  a  spirit  lamp,  and  the  open  extremity  plunged  into  a  vessel  of  mercury, 
a  portion  of  which  rises  into  the  bulb  when  the  latter  cools,  replacing  the 
air  which  had  been  expanded  and  driven  out  by  the  heat.  By  again  applying 
the  flame,  and  causing  this  mercury  to  boil,  the  remainder  of  the  air  is  easily 
expelled,  and  the  whole  space  filled  with  mercurial  vapour,  on  the  condensa- 
tion of  which  the  metal  is  forced  into  the  instrument  by  the  pressure  of  the 
air,  until  it  becomes  completely  filled.  The  thermometer  thus  filled  is  now 
to  be  heated  until  so  much  mercury  has  been  driven  out  by  the  expansion 
of  the  remainder,  that  its  level  in  the  tube  shall  stand  at  common  tempera- 
tures at  the  point  required.  This  being  satisfactorily  adjusted,  the  heat  is 
once  more  applied,  until  the  column  rises  quite  to  the  top ;  and  then  the 
extremity  of  the  tube  is  hermetically  sealed  by  the  blowpipe.  The  retraction 
of  the  mercury  on  cooling  now  leaves  an  empty  space  in  the  upper  part  of 
the  tube,  which  is  essential  to  the  perfection  of  the  instrument. 

The  thermometer  has  yet  to  be  graduated ;  and  to  make  its  indications 
comparable  with  those  of  other  instruments,  a  scale,  having  certain  fixed 
points,  at  the  least  two  in  number,  must  be  adapted  to  it. 

It  has  been  observed,  that  the  temperature  of  melting  ice,  that  is  to  say, 
of  a  mixture  of  ice  and  water,  is  always  constant ;  a  thermometer,  already 
graduated,  plunged  into  such  a  mixture,  always  marks  the  same  degree  of 
temperature,  and  a  simple  tube  filled  in  the  manner  described,  and  so  treated, 
exhibits  the  same  effect  in  the  unchanged  height  of  the  little  mercurial 
column,  when  tried  from  day  to  day.  The  freezing-point  of  water,  or  melting- 
point  oif  ice,  constitutes  then  one  of  the  invariable  temperatures  demanded. 

Another  is  to  be  found  in  the  boiling-point  of  water,  which  is  always  the 
same  under  similar  circumstances.  A  clean  metallic  vessel  is  taken,  into 
which  pure  water  is  put  and  made  to  boil ;  a  thermometer  placed  in  the 
boiling  liquid  just  so  deep  as  is  necessary  to  cover  the  bulb,  invariably  marks 
the  same  degree  of  temperature  so  long  as  the  height  of  the  barometer  re- 
mains unchanged. 

The  tube  having  been  carefully  marked  with  a  file  at  these  two  points,  it 
remains  to  divide  the  interval  into  degrees ;  this  is  entirely  arbitrary.  In 
the  greater  part  of  Europe  and  in  America,  the  scale  called  centigrade  is  em- 
ployed ;  the  space  in  question  being  divided  into  100  parts,  the  zero  being 
placed  at  the  freezing  point  of  water.  The  scale  is  continued  above  and 
below  these  points,  numbers  below  0  being  distinguished  by  the  negative 
sign. 

In  England  the  very  inconvenient  division  of  Fahrenheit  is  still  in  use  ; 
the  above  space  is  divided  into  180  degrees,  but  the  zero,  instead  of  starting 
from  the  freezing-point  of  water,  is  placed  32  degrees  below  it,  so  that  the 
temperature  of  ebullition  is  expressed  by  the  number  212°. 

The  plan  of  Reaumur  is  nearly  confined  to  a  few  places  in  the  north  of 
Germany  and  to  Russia ;  in  this  scale  the  freezing-point  of  water  is  made 
0°,  and  the  boiling-point  80°. 

It  is  unfortunate  that  an  uniform  system  has  not  been  generally  adopted 
in  graduating  thermometers ;  this  would  render  unnecessary  the  labour  which 
now  so  frequently  has  to  be  performed  of  translating  the  language  of  one 
scale  into  that  of  another.  To  effect  this,  presents,  however,  no  great  difl&- 
culty.  Let  it  be  required,  for  example,  to  know  the  degree  of  Fahrenheifa 
scale  which  corresponds  to  60°  centigrade. 

100°  C.  ==  180°  F.,  or  6°  C.  =  9°  F. 

Consequently, 

5  :  9  »  60  :  108. 


HEAT. 


43 


But,  then,  as  Fahrenheit's  scale  commences  with  32°  instead  of  0°,  that 
number  must  be  added  to  the  result,  making  60°  C.  =  140°  F. 

The  rule  then  will  be  the  following : — To  convert  centigrade  degrees  into 
Fahrenheit  degrees,  multiply  by  9,  divide  the  product  by  5,  and  add  32 ;  to 
convert  Fahrenheit  degrees  into  centigrade  degrees,  subtract  32,  multiply 
by  5,  and  divide  by  9. 

The  reduction  of  negative  degrees,  or  those  below  zero  of  either  scale, 
presents  rather  more  apparent  difficulty ;  a  little  consideration,  however, 
will  render  the  method  obvious,  the  interval  between  the  two  zero-points 
being  borne  in  mind. 

Mercury  is  usually  chosen  for  making  thermometers,  on  account  of  its 
regularity  of  expansion  within  certain  limits,  and  because  it  is  easy  to  have 
the  scale  of  great  extent,  from  the  large  interval  between  the  freezing  and 
boiling-points  of  the  metal.  Other  substances  are  sometimes  used ;  alcohol 
is  employed  for  estimating  very  low  temperatures. 

Air-thermometers  are  also  used  for  some  few  particular  purposes ;  indeed, 
the  first  thermometer  ever  made  was  of  this  kind.  There  are  two  modifica- 
tions of  this  instrument ;  in  the  first,  the  liquid  into  which  the  tube  dips  is 
open  to  the  air,  and  in  the  second  (fig.  21),  the  atmosphere  is  completely 
excluded.  The  effects  of  expansion  are  in  the  one  case  complicated  with 
those  arising  from  changes  of  pressure,  and  in  the  other  cease  to  be  visible 
at  all  when  the  whole  instrument  is  subjected  to  alterations  of  temperature, 
because  the  air  in  the  upper  and  lower  reservoir,  being  equally  aff'ected  by 
such  changes,  no  alteration  in  the  height  of  the  fluid  column  can  occur. 
Accordingly,  such  instruments  are  called  differential  thermometers,  since 
they  serve  to  measure  diflFerences  of  temperatures  between  the  two  portions 
of  air,  while  changes  afi'ecting  both  alike  are  not  indicated.  Fig.  22  shows 
another  form  of  the  same  instrument. 


Fig.  21. 


Fig.  22. 


The  air-thermometer  may  be  employed  for  measuring  all  temperatures, 
from  the  lowest  to  the  highest ;  M.  Pouillet  has  described  one  by  which  the 
heat  of  an  air-furnace  could  be  measured.  The  reservoir  of  this  instrument 
is  of  platinum,  and  it  is  connected  with  a  piece  of  apparatus  by  which  the 
increase  of  volume  experienced  by  the  included  air  is  determined. 

All  bodies  are  enlarged  in  their  dimensions  by  the  application  of  heat, 
and  reduced  by  its  abstraction,  or,  in  other  words,  contract  on  being  artifi- 


44^ 


HEAT. 


oially  cooled ;  this  effect  takes  place  to  a  comparatively  small  extent  -with 
solids,  to  a  larger  amount  in  liquids,  and  most  of  all  in  the  case  of  gases. 

Each  solid  and  liquid  has  a  rate  of  expansion  peculiar  to  itself;  gases,  on 
the  contrary,  all  expand  alike  for  the  same  increase  of  heat. 

The  difference  of  expansibility  among  solids  is  very  easily  illustrated  by 
the  following  arrangement:  a  thin  straight  bar  of  iron  is  firmly  fixed  by 
numerous  rivets,  to  a  similar  bar  of  brass ;  so  long  as  the  temperature  at 
"which  the  two  metals  were  united  remains  unchanged.^the  compound  bar 
preserves  its  straight  figure;  but  any  alteration  of  temperature  gives  rise  to 
a  corresponding  curvature.  Brass  is  more  dilatable  than  iron ;  if  the  bar 
be  heated,  therefore,  the  former  expands  more  than  the  latter,  and  forces 
the  straight  bar  into  a  curve,  whose  convex  side  is  the  brass ;  if  it  be  arti- 
ficially cooled,  the  brass  contracts  more  than  the  iron,  and  the  reverse  of 
this  effect  is  produced. 


Fig.  23. 


This  fact  has  received  a  most  valuable  application.  It  is  not  necessary 
lo  insiij^  on  the  importance  of  possessing  instruments  for  the  accurate  mea- 
surement of  time ;  such  are  absolutely  indispensable  to  the 
figr  24.  successful  cultivation  of  astronomical  science,  and  not  less  use- 
ful to  the  navigator,  from  the  assistance  they  give  him  in  find- 
ing the  longitude  at  sea.  For  a  long  time,  notwithstanding  the 
perfection  of  finish  and  adjustment  bestowed  upon  clocks  and 
watches,  an  apparently  insurmountable  obstacle  presented 
itself  to  their  uniform  and  regular  movement;  this  obstacle 
was  the  change  of  dimensions  to  which  the  regulating  parts  of 
the  machine  were  subject  by  alterations  of  temperature.  A 
clock  may  be  defined  as  an  instrument  for  registering  the  nun^ 
ber  of  beats  made  by  a  pendulum :  now  the  time  of  oscillation 
of  a  pendulum  de-pends principally  upon  its  length ;  any  altera- 
tion in  this  condition  will  seriously  affect  the  rate  of  the  clock. 
The  material  of  which  the  rod  of  the  pendulum  is  composed  is 
subject  to  expansion  and  contraction  by  changes  of  tempera- 
ture ;  so  that  a  pendulum  adjusted  to  vibrate  seconds  at  60° 
(15°-5C)  would  go  too  slow  when  the  temperature  rose  to  70° 
(21°-1C),  from  its  elongation,  and  too  fast  when  the  tempera- 
ture fell  to  50°  (10°C),  from  the  opposite  cause. 

This  great  difficulty  has  been  overcome  ;  by  making  the  rod 
of  a  number  of  bars  of  iron  and  brass,  or  iron  and*  zinc, 
metals  whose  rates  of  expansion  are  different,  and  arranging 
these  bars  in  such  a  manner  that  the  expansion  in  one  direction 
of  the  iron  shall  be  exactly  compensated  by  that  in  the  oppo- 
site direction  of  the  brass  or  zinc,  it  is  possible  to  maintain 
under  all  c'rcumstances  of  temperature  fin  invariable  distance  between  the 
point?  of  If  jspensiou  and  of  oscillation.     This  is  often  called  the  gridiron 


HEAT. 


45 


■ 


Fig.  26. 


pendulum  ;  fig.  24  will  clearly  illustrate  its  principle ;  the  shaded      Fig.  26. 
bars  are  supposed  to  be  iron  and  the  others  brass. 

A  still  simpler  compensation  pendulum  (fig,  25)  is  thus  con- 
structed. The  weight  or  bob,  instead  of  being  made  of  a  disc 
of  metal,  consists  of  a  cylindrical  glass  jar  containing  mercury, 
which  is  held  by  a  stirrup  at  the  extremity  of  the  steel  pendulum- 
rod.  The  same  increase  of  temperature  which  lengthens  this  rod, 
causes  the  volume  of  the  mercury  to  enlarge,  and  its  level  to  rise 
in  the  jar ;  the  centre  of  gravity  is  thus  elevated,  and  by  properly 
adjusting  the  quantity  of  mercury  in  the  glass,  the  virtual  length 
of  the  pendulum  may  be  made  constant. 

In  watches,   the   governing  power  is   a  horizontal  weighted 
wheel,  set  in  motion  in  one  direction  by  the  machine  itself,  and  in 
the  other  by  a  fine  spiral  spring.     The  rate  of  going  depends 
greatly  on  the  diameter  of  this  wheel,  and  the  diameter  is  of 
necessity  subject  to  variation  by  change  of  temperature.     To 
remedy  the  evil  thus  involved,  the  circumference  of  the  balance- 
wheel  is  made  of  two  metals  having  different  rates  of  expansion, 
fast  soldered  together,  the  most  expansible  being  on  the  outside. 
The  compound  rim  is  also  cut  through  in  two  or  more  places,  as 
represented  in  fig.  26.     When  the  watch  is  exposed  to  a  high  tempera- 
ture, and  the  diameter  of  the  wheel  becomes  enlarged  by  expansion,  each 
segment  is  made,  by  the  same  agency,  to  assume  a 
sharper  curve,  whereby  its  centre   of  gravity  is 
thrown  inwards,  and  the   expansive   effect  com- 
pletely compensated.    Many  other  beautiful  appli- 
cations of  the  same  principle  might  be  pointed 
out;  the  metallic  thermometer  of  M.  Breguet  is 
one  of  these. 

Mr.  Daniell  very  skilfully  applied  the  expansion 
of  a  rod  of  metal  to  the  measurement  of  tempera- 
tures above  those  capable  of  being  taken  by  the 
thermometer.  A  rod  of  iron  or  platinum,  about 
five  inches  long,  is  dropped  into  a  tube  of  black- 
lead  ware ;  a  little  cylinder  of  baked  porcelain  is 
put  over  it,  and  secured  in  its  place  by  a  platinum  strap  and  a  wedge  of 
porcelain.  When  the  whole  is  exposed  to 
heat,  the  expansion  of  the  bar  drives 
forward  the  cylinder,  which  moves  with  a 
certain  degree  of  friction,  and  shows,  by 
the  extent  of  its  displacement,  the  length- 
ening which  the  bar  had  undergone.  It 
remains,  therefore,  to  measure  the  amount 
of  this  displacement,  which  must  be  very 
small,  even  when. the  heat  has  been  ex- 
ceedingly intense.  This  is  effected  by  the 
contrivance  shown  in  fig.  27,  in  which 
the  motion  of  the  longer  arm  of  the 
lever  carrying  the  vernier  of  the  scale  is 
multipled  by  10,  in  consequence  of  its 
superior  length.  The  scale  itself  is  made 
comparable  with  that  of  the  ordinary 
thermometer,  by  plunging  the  instrument 
into  a  bath  of  mercury  near  its  point  of 
congelation,  and  afterwards  into  another  of  the  same  metal  in  a  boiling 
state,  and  marking  off  the  interval.     'Qy  this  instrument  the  melting-point 


Fig.  27. 


46^  HEAT. 

of  cast  iron  was  fixed  at  2786°  Fahrenheit  (1530°C),  and  the  greatest. heat 
of  a  good  wind-furnace  at  about  3300°  (1815°C). 

.  The  actual  amount  of  expansion  which  diflferent  solids  undergo  by  the 
same  increase  of  heat,  has  been  carefully  investigated.  The  following  are 
some  of  the  results  obtained  by  MM.  Lavoisier  and  Laplace.  The  fraction 
indicates  the  amount  of  expansion  in  length  suffered  by  rods  of  the  under- 
mentioned bodies  in  passing  from  32°  (0°C)  to  212°  (100°C). 


English  flint  glass 

TTi'S 

Soft  iron 

¥«2 

Common  French  glass 

ri^T 

Gold 

Glass  without  lead     . 

ttVi 

Copper 

Another  specimen 

Tir^ff 

Brass 

Steel  untempered 

9?T 

Silver  . 

.      T^T 

Tempered  steel 

T 

Lead 

^r 

Prom  the  linear  expansion,  the  cubic  expansion  (or  increase  of  volume) 
may  be  easily  calculated.  When  an  approximation  only  is  wanted,  it  will  be 
sufficient  to  triple  the  fraction  expressing  the  increase  in  one  dimension. 

Metals  appear  to  expand  pretty  uniformly  for  equal  increments  of  heat 
within  the  limits  stated,  but  above  the  boiling-point  of  water  the  rate  of 
expansion  becomes  irregular  and  more  rapid. 

The  force  exerted  in  the  act  of  expansion  is  very  great ;  in  laying  down 
railways,  building  iron  bridges,  erecting  long  ranges  of  steam-pipes,  and  in 
executing  all  works  of  the  kind  in  which  metal  is  largely  used,  it  is  indis- 
pensable to  make  provision  for  these  changes  of  dimensions. 

A  very  useful  little  application  of  expansion  by  heat  is  that  to  the  cutting 
of  glass  by  a  hot  iron ;  this  is  constantly  practised  in  the  laboratory  for  a 
great  variety  of  purposes.  The  glass  to  be  cut  is  marked  with  ink  in  the 
wished-for  direction,  and  then  a  crack  commenced  by  any  convenient  method, 
at  some  distance  from  the  desired  line  of  fracture,  may  be  led  by  the  point 
of  a  heated  iron  rod  along  the  latter  with  the  greatest  precision. 

Expansion  of  Fluids. — The  dilatation  of  a  fluid  may  be  determined  by  fill- 
ing with  it  a  thermometer,  in  which  the  relation  between  the  capacity  of  the 
ball  and  that  of  the  stem  is  exactly  known,  and  observing  the  height  of  the 
column  at  different  temperatures.  It  is  necessary  in  this  experiment  to  take 
into  account  the  effects  of  the  expansion  of  the  glass  itself,  the  observed  re- 
sult being  evidently  the  difference  of  the  two. 

Liquids  vary  exceedingly  in  this  particular.  The  following  table  is  taken 
from  P^clet's  Elemens  de  Physique. 

Apparent  Dilatation  in  Glass  between  32°  (0°C)  and  212°  (100°C). 

Water 2I 

Hydrochloric  acid,  sp.  gr.  1-137          .         .         •         •  2V 

Nitric  acid,  sp.  gr.  1*4 jf 

Sulphuric  acid,  sp.  gr.  1*85 Xf 

Ether  ^ yV 

Olive  oil Y2 

Alcohol ^ 

Mercury -si 

Most  of  these  numbers  must  be  taken  as  representing  mean  results.  For 
there  are  few  fluids  which,  like  mercury,  expand  regularly  between  these 
temperatures.  Even  mercury  above  212°  (lOOoC)  expands  irregularly,  as 
the  following  table  shows. 


HEAT 


47 


Absolute  Expansion  of  Mercury  for  180°. 

Between  32°  (0°C)  and  212°  (100°C)  ....      s\-^ 

Between  212°  (100°C)  and  392°  (200°C)   ....         5^35 
Between  392°  (200°C)  and  572°  (300°C)        ....     3^3. 

The  absolute  amount  of  expansion  of  mercury  is,  for  many  reasons,  a 
point  of  great  importance ;  it  has  been  very  carefully  determined  by  a  me- 
thod independent  of  the  expansion  of  the  containing  vessel.  The  apparatus 
employed  for  this  purpose  by  MM.  Dulong  and  Petit  is  shown  in  fig.  28,  di- 
vested, however,  of  many  of  its  subordinate  parts.  It  consists  of  two  up- 
right glass  tubes,  connected  at  their  bases  by  a  horizontal  tube  of  much 
smaller  dimensions.  Since  a  free  communication  exists  between  the  two 
tubes,  mercury  poured  into  the  one  will  rise  to  the  same  level  in  the  other, 
provided  its  temperature  is  the  same  in  both  tubes ;  when  this  is  not  the 
case,  the  hottest  column  will  be  the  tallest,  because  the  expansion  of  the 
metal  diminishes  its  specific-gravity,  and  the  law  of  hydrostatic  equilibrium 
requires  that  the  heights  of  such  columns  should  be  inversely  as  their  den- 
sities. By  the  aid  of  the  outer  cylinders,  one  of  the  tubes  is  maintained 
constantly  at  32°  (0°C),  while  the  other  is  raised,  by  means  of  heated  water 
or  oil,  to  any  required  temperature.  The  perpendicular  heights  of  the 
columns  may  then  be  read  off  by  a  horizontal  micrometer  telescope,  moving 
on  a  vertical  divided  scale. 


Fig.  28 


These  heights  represent  volumes  of  equal  weight,  because  volumes  of 
equal  weight  bear  an  inverse  proportion  to  the  densities  of  the  liquids,  so 
that  the  amount  of  expansion  admits  of  being  very  easily  calculated.  Thus, 
let  the  column  at  32°  (0°C)  be  6  inches  high,  and  that  at  212°  (100°C)  6108 
inches,  the  increase  of  height,  108  on  6,000,  or  -^^.-^  part  of  the  whole,  must 
represent  the  absolute  cubical  expansion. 

The  indications  of  the  mercurial  thermometer  are  inaccurate  when  very 
high  ranges  of  temperature  are  concerned,  from  the  increased  expansibility 
of  the  metal ;  on  this  account,  a  certain  correction  is  necessary  in  many  ex- 
periments, and  tables  for  this  purpose  have  been  drawn  up. ' 

An  exception  to  the  regularity  of  expansion  in  fluids,  exists  in  the  case 
of  water;  it  is  so  remarkable,  and  its  consequences  so  important,  that  it  is 
necessary  to  advert  to  it  particularly. 

Let  a  large  thermometer-tube  be  filled  with  water  at  the  common  tempe- 

1  Below  400°  Fahrenheit  (204O-4C)  the  error  may  be  neglected;  at  500°  (260OC)  it  is  alxmt 
1";  at  630°  (332°-5C)  6°. — Regnault. 


48  HEAT. 

V 

rature  of  the  air,  and  then  artificially  cooled.  The  liquid  will  be  observed 
to  contract  regularly,  until  the  temperature  falls  to  abc/lit  40°  (4°-4C),  or  S° 
above  the  freezing-point.  After  this,  a  farther  reduction  of  temperature 
causes  expansion  instead  of  contraction  in  the  volume  of  the  water,  and  this 
expansion  continues  until  the  liquid  arrives  at  its  point  of  congelation,  when 
60  sudden  and  violent  an  enlargement  takes  place,  that  the  vessel  is  almost 
invariably  broken.  At  the  temperature  of  40°  (4° -40),  or  more  correctly, 
perhaps,  39°-5  (4°'1C),  water  is  at  its  maximum  density;  increase  or  dimi- 
nution of  heat  produces  upon  it,  for  a  short  time,  the  same  effect. 

A  beautiful  experiment  of  Dr.  Hope  illustrates  the  same  fact.  If  a  tall 
jar  filled  with  water  at  50°  (10°C)  or  60°  (15°-5C)  and  having  in  it  two 
small  thermometers,  one  at  the  bottom  and  the  other  near  the  surface,  be 
placed  at  rest  in  a  very  cold  room,  the  following  changes  will  be  observed. 
The  thermometer  at  the  bottom  will  fall  more  rapidly  than  that  at  the  top, 
until  it  has  attained  the  temperature  of  40°  (4° -40)  after  which  it  will  re- 
main stationary.  At  length  the  upper  thermometer  will  also  mark  40° 
(4° -40)  but  still  continue  to  sink  as  rapidly  as  before,  while  that  at  the  bot- 
tom remains  stationary.  It  is  easy  to  explain  these  effects :  the  water  in 
the  upper  part  of  the  jar  is  rapidly  cooled  by  contact  with  the  air ;  it  be- 
comes denser  in  consequence,  and  falls  to  the  bottom,  its  place  being  sup- 
plied by  the  lighter  and  warmer  liquid,  which  in  its  turn  suffers  the  same 
change ;  and  this  circulation  goes  on  tintil  the  whole  mass  of  water  has  ac- 
quired its  condition  of  maximum  density,  that  is,  until  the  temperature  has 
fallen  to  40°  (4° -40).  Beyond  this,  loss  of  heat  occasions  expansion  instead 
of  contraction,  so  that  the  very  cold  water  on  the  surface  has  no  tendency 
to  sink,  but  rather  the  reverse. 

This  singular  anomaly  in  the  behaviour  of  water  is  attended  by  the  most 
beneficial  consequences,  in  shielding  the  inhabitants  of  the  waters  from  ex- 
cessive cold.  The  deep  lakes  of  the  North  American  Continent  never  freeze, 
the  intense  and  prolonged  cold  of  the  winters  of  those  regions  being  insuffi- 
cient to  reduce  the  temperature  of  such  masses  of  water  to  40°  (4° -40). 
Ice,  however,  of  great  thickness  forms  over  the  shallow  portions,  and  the 
rivers,  and  accumulates  in  mounds  upon  the  beaches,  where  the  waves  are 
driven  up  by  the  winds. 

Sea-water  has  a  maximum  density  at  the  same  temperature  as  fresh 
water.  The  depths  of  the  Polar  Seas  exhibit  this  temperature  throughQut 
the  year,  while  the  surface-water  is  in  summer  much  above,  and  in  winter 
much  below,  40°  (4° -40) ;  in  both  cases  being  specifically  lighter  than  water 
at  that  temperature.  This  gradual  expansion  of  water  cooled  below  40° 
(4° -40)  must  be  carefully  distinguished  from  the  great  and  sudden  increase 
of  volume  it  exhibits  in  the  act  of  freezing,  and  in  which  respect  it  resem- 
bles many  other  bodies  which  expand  on  solidifying.  It  may  be  observed 
that  the  force  thus  exerted  by  freezing  water  is  enormous.  Thick  iron  shells 
quite  filled  with  water,  and  exposed  with  their  fuse-holes  securely  plugged, 
to  the  cold  of  a  Canadian  winter  night,  have  been  found  the  following  morn- 
ing split  ip  fragments.  The  freezing  of  water  in  the  joints  and  crevices  of 
rocks  is  a  most  potent  agent  in  their  disintegration. 

Expansion  of  Gases. — This  is  a  point  of  great  practical  importance  to  the 
chemist,  and  happily  we  have  very  excellent  evidence  upon  the  subject.  The 
following-  four  propositions  exhibit,  at  a  single  view,  the  principal  facts  of 
the  case: — 

1.  All  gases  expand  alike  for  equal  increments  of  heat ;  and  all  vapours, 

when  remote  from  their  condensing-points,  follow  the  same  law. 

2.  The  rate  of  expansion  is  not  altered  by  a  change  in  the  state  of  com 

pression,  or  elastic  force  of  the  gas  itself. 


HEAT.  «9 

8,  The  rate  of  expansion  is  uniform  for  all  degrees  of  heat. 
4.  The  actual  amount  of  expansion  is  equal  to  ^^^  part  of  the  volume  of 
the  gas  at  0°  Fahrenheit,  for  each  degree  of  the  same  scale.' 

It  will  be  unnecessary  to  enter  into  any  description  of  the  methods  of  in- 
vestigation by  which  these  results  have  been  obtained ;  the  advanced  student 
will  find  in  Pouillet's  Elemms  de  Physique,  and  in  the  papers  of  MM.  Magnus' 
and  Regnault  =*  all  the  information  he  may  require. 

In  the  practical  manipulation  of  gases,  it  very  often  becomes  necessary  to 
make  a  correction  for  temperature,  or  to  discover  how  much  the  volume  of 
a  gas  would  be  increased  or  diminished  by  a  particular  change  of  tempera- 
ture ;  this  can  be  effected  with  great  facility.  Let  it  be  required,  for  ex- 
ample, to  find  the  volume  which  100  cubic  inches  of  any  gas  at  60°  (10°C) 
would  become  on  the  temperature  rising  to  60°  (15° -SC). 

The  rate  of  expansion  is  ^\^  of  the  volume  at  0°  for  each  degree ;  or  460 
measures  at  0°  become  461  at  1°,  462  at  2°,  ••  460  -f  50  =  510  at  50°,  and 
460  -f-  60  =  520  at  60°.     Hence 

Meas.  at  50°.  Meas.  at  60°.  Meae.  at  50°.  Meas.  at  60°. 

510  :  620  =  100  :  101-96. 

If  this  calculation  is  required  to  be  made  on  the  centigrade  scale,  it  must 
be  remembered  that  the  zero  of  that  scale  is  the  melting  point  of  ice.  Above 
this  temperature  the  expansion  for  each  degree  of  the  centigrade  scale  is 
_^^  of  the  original  volume. 

This,  and  the  correction  for  pressure,  are  operations  of  very  frequent  oc- 
currence in  chemical  investigations,  and  the  student  will  do  well  to  become 
familiar  with  them. 


Note.  —  Of  the  four  propositions  stated  in  the  text,  the  first  and  second 
have  quite  recently  been  shown  to  be  true  within  certain  limits  only ;  and 
the  third,  although  in  the  highest  degree  probable,  would  be  very  difficult  to 
demonstrate  rigidly ;  in  fact,  the  equal  rate  of  expansion  of  air  is  assumed 
in  all  experiments  on  other  substances,  and  becomes  the  standard  by  which 
the  results  are  measured. 

The  rate  of  expansion  for  the  different  gases  is  not  absolutely  the  same, 
but  the  difference  is  so  small,  that  for  most  purposes  it  may  with  perfect 
safety  be  neglected.  Neither  is  the  state  of  elasticity  altogether  indifferent, 
the  expansion  being  sensibly  greater  for  an  equal  rise  of  temperature  when 
the  gas  is  in  a  compressed  state. 

It  is  important  to  notice,  that  the  greatest  deviations  from  the  rule  are  exhi- 
bited by  those  gases  which,  as  will  hereafter  be  seen,  are  most  easily  lique- 
fied, such  as  carbonic  acid,  cyanogen,  and  sulphurous  acid,  and  that  the  dis- 
crepancies become  smaller  and  smaller  as  the  elastic  force  is  lessened ;  so 
that,  if  means  existed  for  comparing  the  different  gases  in  states  equally  dis- 
tant from  their  points  of  condensation,  there  is  reason  to  believe  that  the 
la\T  would  be  strictly  fulfilled. 

The  experiments  of  MM.  Dulong  and  Petit  give  for  the  rate  of  expansion 
Tj^  of  the  volume  at  0°  :  this  is  no  doubt  too  high.  Those  of  Rudburg  give 
Tflj ;  of  Magnus  ^-*^ ;  and  of  Regnault  ^^^  :  the  fraction  j^j^  is  adopted  in 
the  test  as  a  convenient  number,  sufficiently  near  the  mean  of  the  three  pre- 
ceding, to  answer  all  purposes. 

*0r  the  amount  of  expansion  is  eqnal  to  1492d  part  of  tlie  volume  the  gas  occupies  at 
320F.  for  each  decree  of  Fahrenheit's  scale.  On  the  centigrade  scale  the  expansiou  ie 
l-27.3d  part  of  the  bulk  at  OOC.  —  R.  B. 

■  PoggendorlTs  Anualeu,  iv.  1.  •  Ann.  Chim.  et  Phys.,  3rd  series,  iv  5.  and  v,  62. 

5 


50 


HEAT. 


The  ready  expansibility  of  air  by  heat  gives  rise  to  the  ptenomena  of 
winds.  In  the  temperate  regions  of  the  earth  these  are  very  variable  and 
uncertain,  but  within  and  near  the  tropics  a  much  greater  regularity  pre- 
vails ;  of  this  the  trade-winds  furnish  a  beautiful  example. 

The  smaller  degree  of  obliquity  with  which  the  sun's  rays  fall  in  the 
localities  mentioned,  occasions  the  broad  belt  thus  stretching  round  the  earth 
to  become  more  heated  than  any  other  part  of  the  surface.  The  heat  thus 
acquired  by  absorption  is  imparted  to  the  low- 
est stratum  of  air,  which,  becoming  expanded, 
rises,  and  gives  place  to  another,  and  in  this 
manner  an  ascending  current  is  established, — 
the  colder  and  heavier  air  streaming  in  late- 
rally from  the  more  temperate  regions,  »orth 
and  south,  to  supply  the  partial  vacuum  thus 
occasioned.  A  circulation  so  commenced  will 
be  completed  in  obedience  to  the  laws  of  hydro- 
statics, by  the  establishment  of  counter-cur- 
rents in  the  higher  parts  of  the  atmosphere, 
having  directions  the  reverse  of  those  on  the 
surface.     (Fig.  29.) 

Such  is  the  effect  produced  by  the  unequal 
heating  of  the  equatorial  parts,  or,  more  correctly,  such  would  be  the  effect 
were  it  not  greatly  modified  by  the  earth's  movement  of  rotation. 

As  the  circumference  of  the  earth  is,  in  round  numbers,  about  24,000 
miles,  and  since  it  rotates  on  its  axis,  from  west  to  east,  once  in  24  hours, 
the  equator-ial  parts  must  have  a  motion  of  1000  miles  per  hour;  this  velo- 
city diminishes  rapidly  towards  each  pole,  where  it  is  reduced  to  nothing. 

The  earth  in  its  rotation  carries  with  it  the  atmosphere,  whose  velocity 
of  movement  corresponds,  in  the  absence  of  disturbing  causes,  with  that 
part  of  the  surface  immediately  below  it.  The 
air  which  rushes  towards  the  equator,  to  sup- 
ply the  place  of  that  raised  aloft  by  its  dimin- 
ished density,  brings  with  it  the  degree  of  mo- 
mentum belonging  to  that  portion  of  the 
earth's  surface  from  which  it  set  out,  and  as 
this  momentum  is  less  than  that  of  the  earth, 
under  its  new  position,  the  earth  itself  travels 
faster  than  the  air  immediately  over  it,  thus 
producing  the  effect  of  a  wind  blowing  in  a 
contrary  direction  to  that  of  its  own  motion. 
The  original  north  and  south  winds  are  thus 
deviated  from  their  primitive  directions,  and 
made  to  blow  more  or  less  from  the  eastward, 
so  that  the  combined  effects  of  the  unequal 
heating  and  of  the  movement  of  rotation  is  to  generate  in  the  northern  hemi- 
sphere a  constant  north-east  wind,  and  in  the  southern  hemisphere  an  equally 
constant  south-east  wind.     (Fig.  30.) 

In  the  same  manner  the  upper  or  return  current  is  subject  to  a  change  of 
direction  in  the  reverse  order ;  the  rapidly-moving  wind  of  the  tropics,  trans- 
ferred laterally  towards  the  poles,  is  soon  found  to  travel  faster  than  the 
earth  beneath  it,  producing  the  effect  of  a  westerly  wind,  which  modifies  the 
primary  current. 

The  regularity  of  the  trade-winds  is  much  interfered  with  by  the  neigh- 
bourhood of  large  continents,  which  produce  local  effects  upon  a  scale  suf- 
ficiently great  to  modify  deeply  the  direction  and  force  of  the  wind.  This 
'.s  the  case  in  the  Indian  Ocean.     They  usually  extend  from  about  the  28th 


HEAT.  51 

degree  of  latitude  in  both  hemispheres,  to  within  8°  of  the  equator,  but  are 
subject  to  some  variations  in  this  respect.  Between  them,  and  also  beyond 
their  boundaries,  lie  belts  of  calms  and  light  variable  winds,  and  beyond 
these  latter,  extending  into  higher  latitudes  in  both  hemispheres,  westerly 
winds  usually  prevail.  The  general  direction  of  the  trade- wind  of  the  North- 
ern hemisphere  is  E.N.E.,  and  that  of  the  Southern  hemisphere  E.S.E. 

The  trade-winds,  it  may  be  remarked,  furnish  an  admirable  physical  proof 
of  the  reality  of  the  earth's  movement  of  rotation. 

The  theory  of  the  action  of  chimneys,  and  of  natural  and  artificial  ven- 
tilation, belongs  to  the  same  subject. 

Let  the  reader  turn  to  the  demonstration  given  of  the  Archimedean  hydro- 
static theorem ;  let  him  once  more  imagine  a  body  immersed  in  water,  and 
having  a  density  equal  to  that  of  the  water ;  it  will  remain  in  equilibrium  in 
any  part  beneath  the  surface,  and  for  these  reasons :  —  The  force  which 
presses  it  downwards  is  the  weight  of  the  body  added  to  the  weight  of  the 
column  of  water  above  it;  the  force  which  presses  it  upwards  is  the  weight 
of  a  column  of  water  equal  to  the  height  of  both  conjoined ; — the  density  of 
the  body  is  that  of  water,  that  is,  it  weighs  as  much  as  an  equal  bulk  of  that 
liquid ;  consequently,  the  downward  and  upward  forces  are  equally  balanced, 
and  the  body  remains  at  rest. 

Next,  let  the  circumstances  be  altered;  let  the  Fig.  31. 

body  be  lighter  than  an  equal  bulk  of  water ;  the 
pi-essure  upwards  of  the  column  of  water,  a  c,  fig.  31, 
is  no  longer  compensated  by  the  downward  pressure 
of  the  corresponding  column  of  solid  and  water 
above  it ;  the  former  force  preponderates,  and  the 
body  is  driven  upwards.  If,  on  the  contrary,  the 
body  be  specifically  heavier  than  the  water,  then 
the  latter  force  has  the  ascendancy,  and  the  body 
sinks. 

All  things  so  described  exist  in  a  common  chim- 
ney; the  solid  body,  of  the  same  density  as  that 
of  the  fluid  in  which  it  floats,  is  represented  by 
the  air  in  the  chimney-funnel ;  the  space  a  b  repre- 
sents the  whole  atmosphere  above  it.  When  the  air  inside  and  outside  the 
chimney  is  at  the  same  temperature,  equilibrium  takes  place,  because  the 
downward  tendency  of  the  air  within  is  counteracted  by  the  upward  pressure 
of  that  without. 

Now,  let  the  chimney  be  heated ;  the  air  suffers  expansion,  and  a  portion 
is  expelled ;  the  chimney  therefore  contains  a  smaller  weight  of  air  than  it 
did  before ;  the  external  and  internal  columns  no  longer  balance  each  other, 
and  the  warmer  and  lighter  air  is  forced  upwards  from  below,  and  its  place 
supplied  by  cold  air.  If  the  brick-work,  or  other  material  of  which  the 
chimney  is  constructed,  retain  its  temperature,  this  second  portion  of  air  is 
disposed  of  like  the  first,  and  the  ascending  current  continues,  so  long  as 
the  sides  of  the  chimney  are  hotter  than  the  surrounding  air. 

Sometimes,  owing  to  sudden  changes  of  temperature  in  the  atmosphere, 
the  chimney  may  happen  to  be  colder  than  the  air  about  it.  The  column 
within  forthwith  suffers  contraction  of  volume ;  the  deficiency  is  filled  up 
from  without,  and  the  column  becomes  heavier  than  one  of  similar  height  on 
the  outside ;_  the  result  is,  that  it  falls  out  of  the  chimney,  just  as  the  heavy 
body  sinks  in  the  water,  and  has  its  place  occupied  by  air  from  above.  A 
descending  current  is  thus  produced,  which  may  be  often  noticed  in  summer 
time  by  the  smoke  from  neighbouring  chimneys  finding  its  way  into  rooms 
which  have  been,  for  a  considerable  period,  without  fire. 

The  ventilation  of  mines  has  long  been  conducted  upon  the  same  principle 


52  HEAT. 

and  more  recently  it  has  been  applied  to  dwelling-houses  and  assembly- 
rooms.  The  mine  is  furnished  with  two  shafts,  or  with  one  shaft,  divided 
throughout  by  a  diaphragm  of  boards ;  and  these  are  so  arranged,  that  air 
forced  down  the  one  shall  traverse  the  whole  extent  of  the  workings  before 
it  escapes  by  the  other.  A  fire  kept  up  in  one  of  these  shafts,  by  rarefying 
the  air  within,  and  causing  an  ascending  current,  occasions  fresh  air  to  tra- 
verse every  part  of  the  mine,  and  sweep  before  it  the  noxious  gases,  but  toi 
frequently  present. 

CONDUCTION    OF   HEAT. 

Different  bodies  possess  very  different  conducting  powers  with  respect  to 
heat :  if  two  similar  rods,  the  one  of  iron  and  the  other  of  glass,  be  held  in 
the  flame  of  a  spirit-lamp,  the  iron  will  soon  become  too  hot  to  be  touched, 
while  the  glass  may  be  grasped  with  impunity  within  an  inch  of  the  red-hot 
portion. 

Experiments  made  by  analogous,  but  more  accurate  methods,  have  estab- 
lished a  numerical  comparison  of  the  conducting  powers  of  many  bodies ; 
the  following  may  be  taken  as  a  specimen  : — 


Gold 

.     1000 

Tin 

.     304 

Silver  . 

973 

Lead    . 

179 

Copper     . 

.       898 

Marble    . 

.       28-6 

Iron 

374 

Porcelain     . 

12-2 

Zinc 

.       363 

Fire-clay 

.       11-4 

As  a  class,  the  metals  are  by  very  far  the  best  conductors,  although  much 
difference  exists  between  them ;  stones,  dense  woods,  and  charcoal,  follow 
next  in  order ;  then  liquids  in  general,  and  gases,  whose  conducting  power 
is  almost  inappreciable. 

Under  favourable  circumstances,  nevertheless,  both  liquids  and  gases  may 
become  rapidly  heated ;  heat  applied  to  the  bottom  of  the  containing  vessel 
is  very  speedily  communicated  to  its  contents ;  this,  however,  is  not  so  much 
by  conduction  as  by  convection,  or  carrying.  A  complete  circulation  is  set 
up  ;  the  portions  in  contact  with  the  bottom  of  the  vessel  get  heated,  become 
lighter,  and  rise  to  the  surface,  and  in  this  way  the  heat  becomes  communi- 
cated to  the  whole.  If  these  movements  be  prevented  by  dividing  the  vessel 
into  a  great  number  of  compartments,  the  really  low  conducting  power  of 
the  substance  is  made  evident,  and  this  is  the  reason  why  certain  organic 
fabrics,  as  wool,  silk,  feathers,  and  porous  bodies  in  general,  the  cavities  of 
which  are  full  of  air,  exhibit  such  feeble  powers  of  conduction. 

The  circulation  of  heated  water  through  pipes  is  now  extensively  applied 
to  the  warming  of  buildings  and  conservatories,  and  in  chemical  works  a 
serpentine  metal  tube  containing  hot  oil  is  often  used  for  heating  stills  and 
evaporating  pans  ;  the  two  extremities  of  the  tube  are  connected  with  the 
ends  of  another  spiral  built  into  a  small  furnace  at  a  lower  level,  and  an 
unintermitting  circulation  of  the  liquid  takes  place  as  long  as  heat  is 
applied. 

CHANGE    OF    STATE. 

If  equal  weights  of  water  at  32°  (OoC)  and  water  at  174°  (78°-8C)  be 
mixed,  the  temperature  of  the  mixture  will  be  the  mean  of  the  two  tomper- 
aturea,  or  103°  (39°-4C).  If  the  same  experiment  be  repeated  with  snow, 
or  finely  powdered  ice,  at  32°  (0°C)  and  water  at  174°  (78°  8C),  the  tem- 
perature of  the  whole  will  be  still  only  32°  (0°C),  but  the  ict  will  have  been 
'neltid 


HEAT. 


63 


=  2  lb.  water  at  103°  (39° -40) 


1  lb.  of  water  at  82°  (0°C) 

1  lb.  of  water  at  174°  (78°-8C) 

1  lb.  of  ice  at  32°  (0°C)  I  _  2  lb  water  at  32°  ^0°C^ 

1  lb.  of  water  at  174°  (78°-8C)  /  —  ^  ^^^  ^^^^r  at  6Z    (U  c; 


In  the  last  experiment,  therefore,  as  much  heat  has  been  apparently  lost 
as  would  have  raised  a  quantity  of  water  equal  to  that  of  the  ice  through  a 
range  of  142°  (78° -SC). 

The  heat,  thus  become  insensible  to  the  thermometer  in  effecting  the  lique- 
faction of  the  ice,  is  called  latent  heat,  or,  better,  head  of  fluidity. 

Again,  let  a  perfectly  uniform  source  of  heat  be  imagined,  of  such  inten- 
sity that  a  pound  of  water  placed  over  it  would  have  its  temperature  raised 
10°  (5°'5C)  per  minute.  Starting  with  water  at  32°  (0°C),  in  rather  more 
than  14  minutes  its  temperatm-e  would  have  risen  142°  (78° -8) ;  but  the 
same  quantity  of  ice  at  32°  (0°C),  exposed  for  the  same  interval  of  time, 
would  not  have  its  temperature  raised  a  single  degree.  But,  then,  it  would 
have  become  water ;  the  heat  received  would  have  been  exclusively  employed 
in  effecting  the  change  of  state. 

This  heat  is  not  lost,  for  when  the  water  freezes  it  is  again  evolved.  If  a 
tall  jar  of  water,  covered  to  exclude  dust,  be  placed  in  a  situation  where  it 
shall  be  quite  undisturbed,  and  at  the  same  time  exposed  to  great  cold,  the 
temperature  of  the  water  may  be  reduced  10°  or  more  below  its  freezing- 
point  without  the  formation  of  ice ;  but  then,  if  a  little  agitation  be  com- 
municated to  the  jar,  or  a  grain  of  sand  dropped  into  the  water,  a  portion 
instantly  solidifies,  and  the  temperature  of  the  whole  rises  to  32°  (0°C) ; 
the  heat  disengaged  by  the  freezing  of  a  small  portion  of  the  water  will  have 
been  sufficient  to  raise  the  whole  contents  of  the  jar  10°  (5° -50). 

Tliis  curious  condition  of  instable  equilibrium  shown  by  the  very  oold 
water  in  the  preceding  experiment,  may  be  reproduced  with  a  variety  of 
solutions  which  tend  to  crystallize  or  solidify,  but  in  which  that  change  is 
for  a  while  suspended.  Thus,  a  solution  of  cr;y1^tallized  sulphate  of  soda  iu 
its  own  weight  of  warm  water,  left  to  cool  in  an  open  vessel,  deposits  a  large 
quantity  of  the  salt  in  crystals.  If  the  warm  solution,  however,  be  filtered 
into  a  clean  flask,  which  when  full  is  securely  corked  and  set  aside  to  cool 
undisturbed,  no  crystals  will  be  deposited,  even  after  many  days,  until  the 
cork  is  withdrawn  and  the  contents  of  the  flask  violently  shaken.  Crystal- 
lization then  rapidly  takes  place  in  a  very  beautiful  manner,  and  the  whole 
becomes  perceptibly  warm. 

The  law  thus  illustrated  in  the  case  of  water  is  perfectly  general.  When- 
ever a  solid  becomes  a  liquid,  a  certain  fixed  and  definite  amount  of  heat 
disappears,  or  becomes  latent ;  and  conversely,  whenever  a  liquid  becomes 
a  solid,  heat  to  a  corresponding  extent  is  given  out.  The  amount  of  latent 
heat  varies  much  with  different  substances,  as  will  be  seen  by  the  table :  — 


Water ' 

.  142°  (78°-8C) 

Zinc    . 

.493°  (273°-8C) 

Sulphur   . 

.       145    (80  -50 

Tin 

.       500    (277  -70) 

Lead    . 

.  162    (90  -50) 

Bismuth     . 

.  550    (305  -50) 

When  a  solid  substance  can  be  made  to  liquefy  by  a  weak  chemical  attrac- 
tion, cold  results,  from  sensible  heat  becoming  latent.  This  is  the  principle 
of  the  many  frigorific  mixtures  to  be  found  described  in  some  of  the  older 
chemical  treatises.  When  snow  or  powdered  ice  is  mixed  with  common  salt, 
and  a  thermometer  is  plunged  into  the  mass,  the  mercury  sinks  to  0° 
( — 17° -70,  while  the  whole,  after  a  short  period,  becomes  fluid  by  the 
attraction  between  the  water  and  the  salt ;  such  a  mixture  is  very  often  used 


MM.  De  la  Provostaye  and  Regnault,  Ann.  Chim.  et  Phys.,  3d  series,  viii.  1. 


6* 


54  HEAT, 

in  chemical  experiments  to  cool  receivers  and  condense  the  vapours  of  vola- 
tile liquids.  Powdered  crystallized  chloride  of  calcium  and  snow  produce 
cold  enough  to  freeze  mercury.  Even  powdered  nitrate  of  potassa,  or  sal- 
ammoniac,  dissolved  in  water,  occasions  a  very  notable  depression  of  tem- 
perature ;  in  every  case,  in  short,  in  which  solution  is  unaccompanied  by 
energetic  chemical  action,  cold  is  produced. 

No  relation  is  to  be  traced  between  the  actual  melting-point  of  a  sub- 
stance, and  its  latent  heat  when  in  a  fused  state. 

A  law  of  exactly  the  same  kind  as  that  described  affects  universally  the 
gaseous  condition ;  change  of  state  from  solid  or  liquid  to  gas  is  accompa- 
nied by  absorption  of  sensible  heat,  and  the  reverse  by  its  disengagement. 
The  latent  heat  of  steam  and  other  vapours  may  be  ascertained  by  a  similar 
mode  of  investigation  to  that  employd  in  the  case  of  water. 

When  water  at  32°  (0°C)  is  mixed  with  an  equal  weight  of  water  at  212° 
(100°C),  the  whole  is  found  to  possess  the  mean  of  the  two  temperatures,  or 
122°  (50°C) ;  on  the  other  hand,  1  part  by  weight  of  steam  at  212°  (100°C) 
when  condensed  into  cold  water,  is  found  to  be  capable  of  raising  5-6  parts 
of  the  latter  from  the  freezing  to  the  boiling-point,  or  through  a  range  of 
180°  (100°C).  Now  180  X  5-6  =  1008;  that  is  to  say,  steam  at  212° 
(100°C)  in  becoming  water  at  212°,  parts  with  enough  heat  to  raise  a  weight 
of  water  equal  to  its  own  (if  it  were  possible)  1008°  (560°C)  of  the  ther-. 
mometer.  When  water  passes  into  steam,  the  same  quantity  of  sensible 
heat  becomes  latent. 

The  vapours  of  other  liquids  seem  to  have  less  latent  heat  than  that  of 
water ;  the  following  table  is  by  Dr.  Ure,  and  serves  well  to  illustrate  this 
point : — 

Vapour  of  water 967°   (537°-2C) 

alcohol  442     (246  -60) 

ether 302     (167  -70) 

petroleum  178       (98  -80) 

"  oil  of  turpentine 178       (98  -80) 

"         nitric  acid 532     (295  -SC) 

"         liquor  ammoniaB 837     (145  -OC) 

"         vinegar 875     (486  -IC) 

Ebullition  is  occasioned  by  the  formation  of  bubbles  of  vapour  within  the 
body  of  the  evaporating  liquid,  which  rise  to  the  surface  like  bubbles  of 
permanent  gas.  This  occurs  in  different  liquids  at  very  different  tempera- 
tures ;  under  the  same  circumstances,  the  boiling-point  is  quite  constant, 
and  often  becomes  a  physical  character  of  great  importance  in  distinguishing 
liquids  which  much  resemble  each  other.  A  few  cases  may  be  cited  in 
illustration: — 

Substance.  Boiling-point. 

^           Ether  96°  (35°-5C) 

Bisulphide  of  carbon 115  (46  -IC) 

Alcohol  177  (80  -SC) 

Water 212  (100  C) 

Nitric  acid,  strong 248  (120  C) 

Oil  of  turpentine 312  (155  -50) 

Sulphuric  acid , 620  (326  -20) 

Mercury  662  (350  C) 

For  ebullition  to  take  place,  it  is  necessary  that  the  elasticity  of  the  vapour 
should  be  able  to  overcome  the  cohesion  of  the  liquid  and  the  pressure  upon 
its  surface ;  hence  the  extent  to  which  the  boiling-point  may  be  modified. 

Water,  under  the  usual  pressure  of  the  atmosphere,  boils  at  212°  (100°C) ; 


HEAT.  55 

in  a  partially  exhausted  receiver  or  on  a  mountain-top  it  boils  at  a  much 
lower  temperature  ;  and  in  the  best  vacuum  of  an  excellent  air-pump,  over 
oil  of  vitriol,  which  absorbs  the  vapour,  it  will  often  enter  into  violent 
ebullition  while  ice  is  in  the  act  of  forming  upon  the  sui-face. 

On  the  other  hand,  water  confined  in  a  very  strong  metallic  vessel  may  be 
restrained  from  boiling  by  the  pressure  of  its  own  vapour  to  an  almost  un- 
limited extent;  a  temperature  of  350°  (177°C)  or  400°  (204°C)  is  very  easily 
obtained  ;  and,  in  fact,  it  is  said  that  it  may  be  made  red-hot,  and  yet  retain 
its  fluidity. 

There  is  a  very  simple  and  beautiful  experiment  illustra- 
tive of  the  effect  of  diminished  pressure  in  depressing  the  Fig.  32. 
boiling  point  of  a  liquid.  A  little  water  is  made  to  boil  for 
a  few  minutes  in  a  flask  or  retort  (fig.  32)  placed  over  a  lamp, 
until  the  air  has  been  chased  out,  and  the  steam  issues  freely 
from  the  neck.  A  tightly  fitting  cork  is  then  inserted,  and 
the  lamp  at  the  same  moment  withdrawn.  When  the 
ebullition  ceases  it  may  be  renewed  at  pleasure  for  a  con- 
siderable time  by  the  affusion  of  cold  water,  Avhich,  by  con- 
densing the  vapour  within,  occasions  a  partial  vacuum. 

The  nature  of  the  vessel,  or  rather,  the  state  of  its  sur- 
face, exercises  an  influence  upon  the  boiling-point,  and  this 
to  a  much  greater  extent  than  was  formerly  supposed.  It 
has  long  been  noticed  that  in  a  metallic  vessel  water  boils,  under  the  same 
circumstances  of  pressure,  at  a  temperature  one  or  two  degrees  below  that 
at  which  ebullition  takes  place  in  glass ;  but  it  has  lately  been  shown '  that 
by  particular  management  a  much  greater  difference  can  be  observed.  If 
two  similar  glass  flasks  be  taken,  the  one  coated  in  the  inside  with  a  film  of 
shellac,  and  the  other  completely  cleansed  by  hot  sulphuric  acid,  water 
heated  over  a  lamp  in  the  first  will  boil  at  211°  (99° -40),  while  in  the  second 
it  will  often  rise  to  221°  (105°C)  or  even  higher ;  a  momentary  burst  of 
vapour  then  ensues,  and  the  thermometer  sinks  a  few  degrees,  after  which 
it  rises  again.  In  this  state  the  introduction  of  a  few  metallic  filings,  or 
angular  fragments  of  any  kind,  occasions  a  lively  disengagement  of  vapour, 
while  the  temperature  sinks  to  212°  (100°C),  and  there  remains  stationary. 
These  remarkable  effects  must  be  attributed  to  an  attraction  between  the 
surface  of  the  vessel  and  the  liquid.^ 

*  Marcet,  Ann.  Chim.  et  Phys.,  3d  scries,  v.  449. 

'  A  remarkable  modification  of  the  relation  between  the  temperature  of  liquids  and  tli» 
vessel  containing  them,  results  where  the  repulsive  action  predominates.  When  a  small 
quantity  of  water  is  thrown  into  a  red-hot  platinum  crucible,  it  assumes  a  spheroidal  form, 
presents  no  appearance  of  ebullition,  but  only  a  rotary  motion,  and  evaporates  very  slowly; 
but  when  the  temperature  falls  to  300°,  this  spheroidal  condition  is  lost,  the  liquid  boils  and 
is  soon  dissipated.  In  the  spheroidal  state  there  is  no  contact  between  the  water  and  metal, 
in  consequence  of  the  high  tension  of  the  small  quantity  of  vapour  which  is  formed  anJ 
surrounds  the  globule,  but  on  the  fall  in  temperature,  the  tension  lessens  and  with  it  the 
repulsive  action,  contact  takes  place  and  the  heat  is  rapidly  communicated  to  the  liquid, 
which  at  once  is  converted  into  steam.  So  slight  is  the  influence  of  the  caloric  of  the  vessel 
on  the  contained  liquid  in  this  condition,  tliat  if  liquid  sulphurous  acid  be  poured  on  the 
globule,  the  water  is  by  the  sudden  evaporation  of  the  acid  converted  into  ice  at  the  bottom 
of  the  red-hot  crucible.  When  a  liquid  which  boils  at  a  low  temperature,  is  thrown  on  an- 
other heated  nearly  to  ebullition  and  whose  boiling-point  is  high,  the  spheroidal  state  is 
likewise  assumed,  as  water  on  oil,  spirits  of  turpentine,  sulphuric  acid,  &c.,  and  ether  on 
water,  &c. 

As  connected  with  this  phenomenon,  it  has  been  observed  that  perfect  immunity  from  the 
caloric  of  highly  heated  liquids  may  be  obtained  by  previously  moistening  the  part  to  which 
the  application  is  made  with  some  fluid  which  evaporates  at  a  low  temperature.  Thus  the 
hand,  while  moistened  with  ether,  may  be  plunged  into  boiling  water  without  even  the  sen- 
sation of  heat.  When  wet  with  water  it  may  be  dipped  into  melted  lead  without  injury  or 
strong  sensation  of  heat,  and  still  less  is  perceived  if  alcohol  or  ether  be  used.  A  similar 
experiment  ha.s  bcseu  performed  with  melted  cast-iron  as  it  runs  from  the  furnace,  and  th* 


56 


HEAT. 


A  cubic  inch  of  water  in  becoming  steam  under  the  ordinary  pressure  of 
the  atmosphere  expands  into  1696  cubic  inches,  or  nearly  a  cubic  foot. 

Steam,  not  in  contact  with  water,  is  aifected  by  heat  in  precisely  the  same 
manner  as  the  permanent  gases ;  its  rate  of  expansion  and  increase  of  elastic 
force  are  the  same.  When  water  is  present,  however,  this  is  no  longer  the 
case,  but  on  the  contrary,  the  elastic  force  increases  in  a  far  more  rapid 
proportion. 

This  elastic  force  of  steam  in  contact  with  water,  at  different  temperatures, 
has  been  very  carefully  determined  by  MM.  Arago  and  Dulong,  and  very 
lately  by  M.  Regnault.  The  force  is  expressed  in  atmospheres ;  the  abso- 
lute pressure  upon  any  given  surface  can  be  easily  calculated,  allowing 
14-6  lb.  to  each  atmosphere.  The  experiments  were  carried  to  twenty-five 
atmospheres,  at  which  point  the  difiBculties  and  danger  became  so  great  as 
to  put  a  stop  to  the  inquiry ;  ihe  rest  of  the  table  is  the  result  of  calcula- 
tions founded  on  the  data  so  obtained. 

Pressure  of  steam  Corresponding 

in  atmospheres.  temperature. 

F  C 

13 381°  194° 

14 387  197  -7 

15 393  200  -5 

16 398  203  -1 

17 404  206  -2 

18 409  209  -4 

19 414  212  -2 

20 41&  214  -4 

21 423  217  -2 

22 427  219  -4 

23 431  221  -2 

24 436  224  -4 

25 439  226  -1 

30 457  236  -1 

35 473  245  -1 

40 487  252  -7 

45 491  255 

60 511  266  -1 

It  is  a  very  remarkable  fact,  that  the  latent  heat  of  steam  diminishes  as 
the  temperature  of  the  steam  rises,  so  that  equal  weights  of  steam  thrown 
into  cold  water  exhibit  nearly  the  same  heating  power,  although  the  actual 
temperature  of  the  one  portion  may  be  212°  (100°C),  and  that  of  the  other 
250°  (176°-2C)  or  400°  (204o-4C).  This  also  appears  true  with  temperatures 
below  the  boiling-point;  so  that  it  seems,  to  evaporate  a  given  quantity  of 
water  the  same  absolute  amount  of  heat  is  required,  whether  it  be  performed 
slowly  at  the  temperature  of  the  air,  in  a  manner  presently  to  be  noticed,  or 
whether  it  be  boiled  off  under  the  pressure  of  twenty  atmospheres.  It  is 
for  this  reason  that  the  process  of  distillation  in  vacuo  at  a  temperature 
which  the  hand  can  bear,  so  advantageous  in  other  respects,  can  effect  no 
direct  saving  in  fuel.» 

dry  parts  subjected  to  the  radiant  caloric  have  been  found  more  affected  than  that  exposed 
to  the  melted  metal. 

The  immunity  in  the  case  of  using  water  as  the  moistening  agent  arises  from  the  fact  that 
the  temperature  of  the  globule  in  the  spheroidal  state  is  much  below  the  boiling-point  of  the 
liquid.  — R.B. 

'  The  proposition  in  the  t-ext,  of  the  sum  of  the  latent  and  sensible  heatg  of  steam  Unng  a 
constaiit  quantity,  is  known  by  the  name  of  Watt's  law,  having  been  deduced  by  that  illu»- 


Pressure  of  steam 

Corres 

ponding 

in  atmospheres. 

temperature. 

1      

....  212° 

100° 

1-5 

....  234 

112  -2 

2    

.-     251 

121  -2 

2-5 

....  264 

128  -8 

8    

....  275 

135 

3-5 

....  285 

140-5 

4    

....  294 

145-5 

4-5 

....  300 

148  -8 

6    

....  308 

153  -1 

5-5 

....  314 

156  -2 

6    

....  320 

160 

6-5 

....  326 

163  -1 

7    

....  332 

166  -2 

7-5 

....  337 

169  -4 

8    

....  342 

172  -2 

9    

....  351 

177  -2 

10    

....  359 

181  -2 

11     

....  367 

186  -1 

12    

....  374 

190 

HEAT. 


57 


Fig.  34. 


The  economical  applications  of  steam  are  numerous  and  extremely  valu- 
able; they  may  be  divided  into  two  classes:  those  in  which  the  heating 
power  is  employed,  and  those  in  which  its  elastic  force  is  brought  into  use. 

The  value  of  steam  as  a  source  of  heat  depends 
upon  the  facility  with  which  it  may  be  conveyed  to  Fix.  33. 

distant  points,  and  upon  the  large  amount  of  latent 
heat  it  contains,  which  is  disengaged  in  the  act  of 
condensation.  An  invariable  temperature  of  212° 
(100°C),  or  higher,  may  be  kept  up  in  the  pipes  or 
other  vessels  in  which  the  steam  is  contained  by 
the  expenditure  of  a  very  small  quantity  of  the 
latter.  Steam-baths  of  various  forms  are  used  in 
the  arts  with  great  convenience,  and  also  by  the 
scientific  chemist  for  drying  filters  and  other  ob- 
jects where  excessive  heat  would  be  hurtful;  a 
very  good  instrument  of  the  kind  was  contrived 
by  Mr.  Everitt.  It  is  merely  a  small  kettle  (fig. 
83),  surmounted  by  a  double  box  or  jacket,  into 

which  the  substance  to  be  di-ied  is  put,  and  loosely  covered  by  a  card.  The 
apparatus  is  placed  over  a  lamp,  and  may  be  left  without  attention  for  many 
hours.  A  little  hole  in  the  side  of  the  jacket 
gives  vent  to  the  excess  of  steam. 

The  principle  of  the  steam-engine  may 
be  described  in  a  few  words ;  its  mechanical 
details  do  not  belong  to  the  design  of  the 
present  volume.  The  machine  consists  es- 
sentially of  a  cylinder  of  metal,  a  (fig.  34), 
in  which  works  a  closely-fitting  solid  piston, 
the  rod  of  which  passes,  air-tight,  through 
a  stuffing-box  at  the  top  of  the  cylinder, 
and  is  connected  with  the  machinery  to  be 
put  in  motion,  directly,  or  by  the  interven- 
tion of  an  oscillating  beam.  A  pipe  commu- 
nicates with  the  interior  of  the  cylinder,  and 
also  with  a  vessel  surrounded  with  cold 
water,  called  the  condenser,  marked  b  in  the 
sketch,  and  into  which  a  jet  of  cold  water 
can  at  pleasure  be  introduced.  A  sliding- 
valve  arrangement,  shown  at  c,  serves  to 
open  a  communication  between  the  boiler 
and  the  cylinder,  and  the  cylinder  and  the 
condenser,  in  such  a  manner  that  while  the 
steam  is  allowed  to  press  with  all  its  force 
upon  one  side  of  the  piston,  the  other,  open 
to  the  condenser,  is  necessarily  vacuous. 
The  valve  is  shifted  by  the  engine  itself  at 
the  proper  moment,  so  that  the  piston  is  al- 
ternately driven  by  the  steam  up  and  down 
against  a  vacuum.  A  large  air-pump,  not 
shown  in  the  engraving,  is  connected  with  the 
condenser,  and  serves  to  remove  any  air  that  may  enter  the  cylinder,  and 
also  the  water  produced  by  condensation,  together  with  that  which  may  have 
been  injected. 

Such  is  the  vacuum  or  condensing  steam-engine.     In  what  is  called  the 

trious  man  from  experiments  of  his  own.  It  liaa  always  agreed  well  with  the  rouarh  practical 
results  obtained  by  engineers,  and  has  lately  been  confirmed  to  a  great  extent,  aJVhough  not 
completely,  by  a  series  of  elaborate  cxperimonts  by  M,  Uegnault. 


68 


HEAT. 


high-pressure  engine,  the  condenser  and  air-pump  are  suppressed,  and  the 
steam  is  allowed  to  escape  at  once  from  the  cylinder  into  the  atmosphere. 
It  is  obvious  that  in  this  arrangement  the  steam  has  to  overcome  the  whole 
pressure  of  the  air,  and  a  much  greater  elastic  force  is  required  to  produce 
the  same  effect ;  but  this  is  to  a  very  great  extent  compensated  by  the  absence 
of  the  air-pump  and  the  increased  simplicity  of  the  whole  machine.  Large 
engines,  both  on  shore  and  in  steam-ships,  are  usually  constructed  on  the 
condensing  principle,  the  pressure  seldom  exceeding  six  or  seven  pounds  per 
square  inch  above  that  of  the  atmosphere ;  for  small  engines  the  high-pressure 
plan  is,  perhaps,  preferable.     Locomotive  engines  are  of  this  kind. 

A  peculiar  modification  of  the  steam-engine,  employed  in  Cornwall  for 
draining  the  deep  mines  of  that  country,  is  now  getting  into  use  elsewhere 
for  other  purposes.  In  this  machine  economy  of  fuel  is  carried  to  a  most 
extraordinary  extent,  engines  having  been  known  to  perform  the  duty  of 
raising  more  than  100,000,000  lb.  of  water  one  foot  high  by  the  consumption 
of  a  single  bushel  of  coals.  The  engines  are  single-acting ;  the  down-stroke, 
which  is  made  against  a  vacuum,  being  the  effective  one,  and  employed  to 
lift  the  enormous  weight  of  the  pump-rods  in  the  shaft  of  the  mine.  When 
the  piston  reaches  the  bottom,  the  communication  both  with  the  boiler  and 
the  condenser  is  cut  off,  while  an  equilibrium-valve  is  opened,  connecting  the 
upper  and  lower  extremities  of  the  cylinder,  whereupon  the  weight  of  the 
pump-rods  draws  the  piston  to  the  top  and  makes  the  up-stroke.  The  engine 
is  worked  expansively,  as  it  is  termed,  steam  of  high  tension  being  employed, 
which  is  cut  off  at  one-eighth  or  even  one-tenth  of  the  stroke. 

The  process  of  distillation,  which  may  now  be  noticed,  is  very  simple  ;  its 
object  is  either  to  separate  substances  which  rise  in  vapour  at  different  tem- 
peratures, or  to  part  a  volatile  liquid  from  a  substance  incapable  of  volatili- 
zation. The  same  process  applied  to  bodies  which  pass  directly  from  the 
solid  to  the  gaseous  condition,  and  the  reverse,  is  called  sublimation.  Every 
distillatory  apparatus  consists  essentially  of  a  boiler,  in  which  the  vapour  is 
raised,  and  of  a  condenser,  in  which  it  returns  to  the  liquid  or  solid  con- 
dition. In  the  still  employed  for  manufacturing  purposes,  the  latter  is 
usually  a  spiral  metal  tube  immersed  in  a  tub  of  water.  The  common  retort 
and  receiver  constitute  the  simplest  and  most  generally  useful  arrangement 
for  distillation  on  the  small  scale ;  the  retort  is  heated  by  a  lamp  or  a  char- 
Fig.  35. 


H  EAT. 


69 


coal  lire,  and  the  receiver  is  kept  cool,  if  necessary,  by  a  wet  cloth,  or  it  may 
be  surrounded  with  ice.  (Fig.  35.) 

Fis:.36 


Fig.  37 


The  condenser  of  Professor  Liebig  is  a  very  valuable  instru- 
ment in  the  laboratory ;  it  consists  of  a  glass  tube  (fig.  36), 
tapering  from  end  to  end,  fixed  by  perforated  corks  in  the  centre 
of  a  metal  pipe,  provided  with  tubes  so  arranged  that  a  current 
of  cold  water  may  circulate  through  the  apparatus.  By  putting 
a  few  pieces  of  ice  into  the  little  cistern,  the  temperature  of  this 
water  may  be  kept  at  32°  (0°C),  and  extremely  volatile  liquids 
condensed. 

Liquids  evaporate  at  temperatures  below  their  boiling-points ; 
in  this  case  the  evaporation  takes  place  solely  from  the  surface. 
Water,  or  alcohol,  exposed  in  an  open  vessel  at  the  temperature 
of  the  air,  gradually  dries  up  and  disappears  ;  the  more  rapidly, 
the  warmer  and  drier  the  air  above  it. 

This  fact  was  formerly  explained  by  supposing  that  air  and 
gases  in  general  had  the  power  of .  dissolving  and  holding  in 
solution  certain  quantities  of  liquids,  and  that  this  power  in- 
creased with  the  temperature ;  such  an  idea  is  incorrect. 

If  a  barometer-tube  (fig.  37)  be  carefully  filled  with  mercury 
and  inverted  in  the  usual  manner,  and  then  a  few  drops  of  water 
passed  up  the  tube  into  the  vacuum  above,  a  very  remarkable 
effect  will  be  observed ;  —  the  mercury  will  be  depressed  to  a 
small  extent,  and  this  depression  will  increase  with  increase  of 
temperature.  Now,  as  the  space  above  the  mercury  is  void  of 
air,  and  the  weight  of  the  few  drops  of  water  quite  inadequate 
to  account  for  this  depression,  it  must  of  necessity  be  imputed 
to  the  vapour  which  instantaneously  rises  from  the  water  into 
the  vacuum  ;  and  that  this  effect  is  really  due  to  the  elasticity 
or  tension  of  the  aqueous  vapour,  is  easily  proved  by  exposing 
the  barometer  to  a  heat  of  212°  (100°C),  when  the  depression 
of  the  mercury  will  be  complete,  and  it  will  stand  at  the  same 
level  within  and  without  the  tube,  indicating  that  at  that  temper- 
ature the  elasticity  of  the  vapour  is  equal  to  that  of  the  atmo- 
sphere,— a  fact  which  the  phenomenon  of  ebullition  has  already 
shown. 

By  placing  over  the  barometer  a  wide  open  tube  dipping  into  the  mercury 
below,  and  then  filling  this  tube  with  water  at  different  temperatures,  the 


60 


HEAT 


tension  of  the  aqueous  vapour  for  each  degree  of  the  thermometer  may  be 
accurately  determined  by  its  depressing  effect  upon  the  mercurial  column ; 
the  same  power  which  forces  the  latter  down  one  inch  against  the  pressure 
of  the  atmosphere,  would  of  course  elevate  a  column  of  mercury  %  the  same 
height  against  a  vacuum,  and  in  this  way  the  tension  may  be  very  conve- 
niently expressed.  The  following  table  was  drawn  up  by  Dr.  Dalton,  to 
whom  we  owe  the  method  of  investigation. 

Tension  in  inches 
C.  of  mercury. 

0°    0-200 

4-4  0-263 


Temperature. 


40 

60  ...  10  0-375 

60  ...  15-5  0-524 

70  ...  21-1  0-721 

80  ...  26-6  1-000 

90  ...  32-2  1-360 

100  ...  37-7  1-860 

110  ...  43-3  2-530 

120  ...  48-8  3-330 


Temperature, 
C. 


F 

130 
140 
150 
160 
170 
180 
190 
200 
212 


Tension  in  inches 
of  mercury. 

..  54-4  4-34 

..  60  5-74 

..  65-5  7-42 

..  71-1  9-46 

..  76-6  1213 

..  82-2  15-15 

..  87-7  1900 

..  93-3  23-64 

..100  3000 


u 


Other  liquids  tried  in  this  manner  are  found  to  emit 
vapours  of  greater  or  less  tension,  for  the  same  temper- 
ature, according  to  their  different  degrees  of  volatility : 
thus,  a  little  ether  introduced  into  the  tube  depresses  the 
mercury  10  inches  or  more  at  the  ordinary  temperature 
of  the  air;  oil  of  vitriol,  on  the  other  hand,  does  not 
emit  any  sensible  quantity  of  vapour  until  a  much  greater 
heat  is  applied ;  and  that  given  off  by  mercury  itself  in 
warm  summer  weather,  although  it  may  by  very  delicate 
means  be  detected,  is  far  too  little  to  exercise  any  effect 
upon  the  barometer.  In  the  case  of  water,  the  evapora- 
tion is  quite  distinct  and  perceptible  at  the  lowest  tem- 
peratures, when  frozen  to  solid  ice  in  the  barometer-tube ; 
snow  on  the  ground,  or  on  a  house-top,  may  often  be 
noticed  to  vanish,  from  the  same  cause,  day  by  day  in  the 
depth  of  winter,  when  melting  was  impossible. 

There  exists  for  each  vapour  a  state  of  density  which 
it  cannot  pass  without  losing  its  gaseous  condition,  and 
becoming  liquid ;  this  point  is  called  the  condition  of 
maximum  density.  When  a  volatile  liquid  is  introduced 
in  sufficient  quantity  into  a  vacuum,  this  condition  is 
always  reached,  and  then  evaporation  ceases.  Any  at- 
tempt to  increase  the  density  of  this  vapour  by  com- 
pressing it  into  a  smaller  space  will  be  attended  by  the 
liquefaction  of  a  portion,  the  density  of  the  remainder 
being  unchanged.  If  a  little  ether  be  introduced  into  a 
barometer  (fig.  38),  and  the  latter  slowly  sunk  into  a  very 
deep  cistern  of  mercury,  it  will  be  found  that  the  height 
of  the  column  of  mercury  in  the  tube  above  that  in  the 
cistern  remains  unaltered  until  the  upper  extremity  of 
the  barometer  approaches  the  surface  of  the  metal  in  the 
reservoir.  It  will  be  observed  also,  that,  as  the  tube 
sinks,  the  little  stratum  of  liquid  ether  increases  in  thick- 
ness, but  no  increase  of  elastic  force  occurs  in  the  vapour 
above  it,  and,  consequently,  no  increase  of  density ;  for 
tension  and  density  are  always,  under  ordinary  circum- 
stances at  least,  directly  proportionate  to  each  other  iu 
the  same  vapour. 


HEAT.  61 

The  point  of  maximum  density  of  a  vapour  is  dependent  upon  the  tem- 
perature ;  it  increases  rapidly  as  the  temperature  rises.  This  is  -well  shown 
in  the  case  of  water.  Thus,  taking  the  specific  gravity  of  atmospheric  air 
at  212°  (100°C)  =  1000,  that  of  aqueous  vapour  in  its  greatest  possible 
state  of  compression  for  the  temperature  will  be  as  follows : — 

Temperature.  Specific  gravity.  Weight  of  100  cubic  inches. 

F.  C. 

32°         0°    5-G90  0136  grains. 

50        10-     10-293  0-247 

60        15-5  14108  0-338 

100        37-7  46-500  1113 

150        65  5  170-293  4076 

212      100      625000  14-962 

The  last  number  was  experimentally  found  by  M.  Gay-Lussac ;  the  others 
are  calculated  upon  that  by  the  aid  of  Dr.  Dalton's  table  of  tensions. 

Thus,  there  are  two  distinct  methods  by  which  a  vapour  may  be  reduced 
to  the  liquid  form ;  pressure,  by  causing  increase  of  density  until  the  point 
of  maximum  density  for  the  particular  temperature  is  reached ;  and  cold,  by 
which  the  point  of  maximum  density  is  itself  lowered.  The  most  powerful 
effects  are  of  course  produced  when  both  are  conjoined. 

For  example,  if  100  cubic  inches  of  perfectly  transparent  and  gaseous 
vapour  of  water  at  100°  (37°-7C),  in  the  state  above  described,  had  its  tem- 
perature reduced  to  50°  (10°C),  not  less  than  0-87 '  grain  of  fluid  water 
would  necessarily  separate,  or  very  neai'ly  eight-tenths  of  the  whole. 

Evaporation  into  a  space  filled  with  air  or  gas  follows  the  same  law  as 
evaporation  into  a  vacuum ;  as  much  vapour  rises,  and  the  condition  of  max- 
imum density  is  assumed  in  the  same  manner  as  if  the  space  were  perfectly 
empty;  the  sole  difference  lies  in  the  length  of  time  required.  When  a 
liquid  evaporates  into  a  vacuum,  the  point  of  greatest  density  is  attained  at 
once,  while  in  the  other  case  some  time  elapses  before  this  happens ;  the 
particles  of  air  appear  to  oppose  a  sort  of  mechanical  resistance  to  the  rise 
of  the  vapour.     The  ultimate  effect  is,  however,  precisely  the  same. 

When  to  a  quantity  of  perfectly  dry  gas  confined  in  a  vessel  closed  by 
mercury,  a  little  water  is  added,  the  latter  immediately  begins  to  evaporate, 
and  after  some  time  as  much  vapour  will  be  found  to  have  risen  from  it  as 
if  no  gas  had  been  present,  the  quantity  depending  entirely  on  the  temper- 
ature to  which  the  whole  is  subjected.  The  tension  of  this  vapour  will  add 
itself  to  that  of  the  gas,  and  produce  an  expansion  of  volume,  which  will  be 
indicated  by  an  alteration  of  level  in  the  mercury. 

Vapour  of  water  exists  in  the  atmosphere  at  all  times,  and  in  all  situa- 
tions, and  there  plays  a  most  important  part  in  the  economy  of  nature.  The 
proportion  of  aqueous  vapour  present  in  the  air  is  subject  to  great  variation, 
and  it  often  becomes  exceedingly  important  to  determine  its  quantity.  This 
^  easily  done  by  the  aid  of  the  foregoing  principles. 

If  the  aqueous  vapour  be  in  its  condition  of  greatest  possible  density  for 
the  temperature,  or,  as  it  is  frequently,  but  most  incorrectly  expressed,  the 
air  be  saturated  with  vapour  of  water,  the  slightest  reduction  of  tempera- 
ture will  cause  the  deposition  of  a  portion  in  the  liquid  form.  If,  on  the 
contrary,  as  is  almost  always  in  reality  the  case,  the  vapour  of  water  be 
below  its  state  of  maximum  density,  that  is,  in  an  expanded  condition,  it  is 
clear  that  a  considerable  fall  of  temperature  may  occur  before  liquefaction 
commences.     The  degree  at  which  this  takes  place  is  called  the  dew-point, 

*  100  cubic  inches  aqueous  vapours  at  100°  (37°-70),  weighing  1-113  grain,  would  at  SO' 
(10°C),  become  reduced  to  10-29  cubic  inches,  weighing  0-247  graia 

6 


62 


HEAT. 


and  it  is  determined  with  great  facility  by  a  very  simple  method.  A  little 
cup  of  thin  tin-plate  or  silver,  well  polished,  is  filled  with  water  at  the  tem- 
perature of  the  air,  and  a  delicate  thermometer  inserted.  The  water  is  then 
cooled  by  dropping  in  fragments  of  ice,  or  dissolving  in  it  powdered  sal- 
ammoniac,  until  a  deposition  of  moisture  begins  to  make  its  appearance  on 
the  outside,  dimming  the  bright  metallic  surface.  The  temperature  of  the 
dew-point  is  then  read  off  upon  the  thermometer,  and  Compared  with  that 
of  the  air. 

Suppose,  by  way  of  example,  that  the  latter  were  70°  (21°-1C),  and  the 
dew-point  50°  (10°C) ;  the  elasticity  of  the  watery  vapour  present  would 
correspond  to  a  Maximum  density  proper  to  60°  (10°C),  and  would  support 
.a  column  of  mercury  0-375  inch  high.  If  the  barometer  on  the  spot  stood 
at  30  inches,  therefore,  29-625  inches  would  be  supported  by  the  pressure 
of  the  dry  air,  and  the  remaining  0-375  inch  by  the  vapour.  Now  a  cubic 
foot  of  such  a  mixture  must  be  looked  upon  as  made  up  of  a  cubic  foot  of 
dry  air,  and  a  cubic  foot  of  watery  vapour,  occupying  the  same  space,  and 
having  tensions  indicated  by  the  numbers  just  mentioned.  A  cubic  foot,  or 
1728  cubic  inches  of  vapour  at  70°  (21°-1C),  would  become  reduced  by  con- 
traction, according  to  the  usual  law,  to  1G62-8  cubic  inches  at  50°  (10°C) ; 
this  vapour  would  be  at  its  maximum  dcnsitj'',  having  the  specific  gravity 
pointed  out  in  the  table;  hence  1662-8  cubic  inches  would  weigh  4-11  grains. 
The  weight  of  the  aqueous  vapour  contained  in  a  cubic  foot  of  air  will  thus 
be  ascertained.  In  England  the  difference  between  the  temperature  of 
the  air  and  the  dew-point  seldom  reaches  30°  ( — 1°-2C) ;  but  in  the  Deccan, 
with  a  temperature  of  90°  (32° -2C),  the  dew-point  has  been  seen  as  low  as 
29°  ( — 1°-6C)  making  the  degree  of  dryness  61°.' 

Another  method  of  finding  the  proportion  of  moisture  present  in  the  air 
is  to  observe  the  rapidity  with  which  evaporation  takes  place,  and  which  is 
always  in  some  relation  to  the  degree  of  dryness.     The  bulb 
Fig.  39.  of  a  thermometer  is  covered  with  muslin,  and  kept  wet  with 

water ;  evaporation  produces  cold,  as  will  presently  be  seen, 
and  accordingly  the  thermometer  soon  sinks  below  the  ac- 
tual temperature  of  the  air.  When  it  comes  to  rest,  the 
degree  is  noticed,  and  from  a  comparison  of  the  two  tempe- 
ratures an  approximation  to  the  dew-point  can  be  obtained 
by  the  aid  of  a  mathematical  formula  contrived  for  the  pur- 
pose. This  is  called  the  wet-bulb  hygrometer ;  it  is  often 
made  in  the  manner  shown  in  fig.  39,  where  one  thermometer 
serves  to  indicate  the  temperature  of  the  air,  and  the  other 
to  show  the  rate  of  evaporation,  being  kept  wet  by  the 
thread  in  connexion  with  the  little  water  reservoir. 

The  perfect  resemblance  in  every  respect  which  vapours 
bear  to  permanent  gases,  led,  very  naturally,  to  the  idea 
that  the  latter  might,  by  the  application  of  suitable  means, 
be  made  to  assume  the  liquid  condition,  and  this  surmise 
was,  in  the  hands  of  Mr.  Faraday,  to  a  great  extent  verified. 
Out  of  the  small  number  of  such  substances  tried,  not  less 
than  eight  gave  way :  and  it  is  quite  fair  to  infer,  that,  had 
means  of  sufficient  power  been  at  hand,  the  rest  would  have 
shared  the  same  fate,  and  proved  to  be  nothing  more  than 
the  vapours  of  volatile  liquids  in  a  state  very  far  removed 
from  that  of  their  maximum  density.  The  subjoined  table 
represents  the  results  of  Mr.  Faraday's  first  investigations, 


Mr.  Daniell,  Introduction  to  Chemical  Philosophy,  p.  154. 


HEAT.  63 

with  the  pressure  in  atmospheres,  and  the  temperature  at  which  the  con- 
ienaation  took  place.' 

Atmospheres.  Temperature. 

l\  C. 

Sulphurous  acid  2     45°      7o-2 

Sulphuretted  hydrogen 17      60  10 

Carbonic  acid  36      32        0 

Chlorine 4     60  15-5 

Nitrous  oxide  60     46        7  -2 

Cyanogen  3-6  45        7  -2 

Ammonia 6"5  50  10 

Hydrochloric  acid 40     50  10 

The  method  of  proceeding  was  very  simple ;  the  materials  were  sealed  up 
\n  a  strong  narrow  tube  (fig.  40),  together  with  a  little  pressure-gauge,  con- 
Fig.  40. 


sisting  of  a  slender  tube  closed  at  one  end,  and  having  within  it,  near  the 
open  extremity,  a  globule  of  mercury.  The  gas  being  disengaged  by  the 
application  of  heat,  or  otherwise,  accumulated  in  the  tube,  and  by  its  own 
pressure  brought  about  condensation.  The  force  required  for  this  purpose 
was  judged  of  by  the  diminution  of  volume  of  the  air  in  the  gauge. 

Mr.  Faraday  has  since  resumed,  with  the  happiest  results,  the  subject  of 
the  liquefaction  of  the  permanent  gases.  By  using  narrow  green  glass  tubes 
of  great  strength,  powerful  condensing  syringes,  and  an  extremely  low  tem- 
perature, produced  by  means  to  be  presently  described,  defiant  gas,  hydri- 
odic  and  hydrobromic  acids,  phosphoretted  hydrogen,  and  the  gaseous 
fluorides  of  silicon  and  boron,  were  successively  liquefied.  Oxygen,  hydro- 
gen, nitrogen,  nitric  oxide,  carbonic  oxide,  and  coal-gas,  refused  to  liquefy 
at  the  temperature  of — 166°  ( — 74°'4C)  while  subjected  to  pressures  vary- 
ing in  the  diflFerent  cases  from  27  to  58  atmospheres.' 

Sir  Isambard  Brunei,  and,  more  recently,  M.  Thilorier,  of  Paris,  suc- 
ceeded in  obtaining  liquid  carbonic  acid  in  great  abundance.  The  apparatus 
of  M.  Thilorier  (fig.  41)  consists  of  a  pair  of  extremely  strong  metallic  ves- 
sels, one  of  which  is  destined  to  serve  the  purpose  of  a  retort,  and  the  other 
that  of  a  receiver.  They  are  made  either  of  thick  cast-iron  or  gun-metal, 
or,  still  better,  of  the  best  and  heaviest  boiler-plate,  and  are  furnished  with 
stop-cocks  of  a  peculiar  kind,  the  workmanship  of  which  must  be  excellent. 
The  generating  vessel  or  retort  has  a  pair  of  trunnions  upon  which  it  swings 
in  an  iron  frame.  The  joints  are  secured  by  collars  of  lead,  and  every  pre- 
caution taken  to  prevent  leakage  under  the  enormous  pressure  the  vessel 
has  to  bear.  The  receiver  resembles  the  retort  in  every  respect ;  it  has  a 
similar  stop-cock,  and  is  connected  with  the  retort  by  a  strong  copper  tube 
and  a  pair  of  union  screw-joints ;  a  tube  passes  from  the  stop-cock  down- 
wards, and  terminates  near  the  bottom  of  the  vessel. 

The  operation  is  thus  conducted :  2|  lb,  of  bicarbonate  of  soda,  and  6j 
it),  of  water  at  100°  (37°-7C),  are  introduced  into  the  generator ;  oil  of  vitriol 

»  Phil.  Trans,  for  1823,  p.  189. 
'  Phil.  Trans,  for  1845,  p.  15,V 


u 


to  the  amount  of  Ij-  lb.  is  poured  into  a  copper  cylindrical  vessel,  -vvhicli  is 
lowered  down  into  the  mixture,  and  set  upright;  the  stop-cock  is  then 
screwed  into  its  place,  and  forced  home  by  a  spanner  and  mallet.  The  ma- 
chine is  next  tilted  up  on  its  trunnions,  that  the  acid  may  run  out  of  the 
cylinder  and  mix  with  the  other  contents  of  the  generator ;  and  this  mixture 
is  favoured  by  swinging  the  whole  backwards  and  forwards  for  a  few  mi- 
nutes, after  which  it  may  be  suffered  to  remain  a  little  time  at  rest. 

The  receiver,  surrounded  with  ice,  is  next  connected  to  the  generator,  and 
both  cocks  opened ;  the  liquefied  carbonic  acid  distils  over  into  the  colder 
vessel,  and  there  again  in  part  condenses.  The  cocks  are  now  closed,  the 
vessels  disconnected,  the  cock  of  the  generator  opened  to  allow  the  contained 
gas  to  escape ;  and,  lastly,  when  the  issue  of  gas  has  quite  ceased,  the  stop- 
cock itself  unscrewed,  and  the  sulphate  of  soda  turned  out.  This  operation 
must  be  repeated  five  or  six  times  before  any  very  considerable  quantity  of 
liquefied  acid  will  have  accumulated  in  the  receiver.  When  the  receiver 
thus  charged  has  its  stop-cock  opened,  a  stream  of  the  liquid  is  forcibly 
driveti  up  the  tube  by  the  elasticity  of  the  gas  contained  in  the  upper  part 
of  the  vessel. 

It  will  be  quite  proper  to  point  out  to  the  experimenter  the  great  personal 
danger  he  incurs  in  using  this  apparatus,  unless  the  greatest  care  be  taken 
in  its  management.  A  dreadful  accident  has  already  occurred  in  Pari*  by 
the  bursting  of  one  of  the  iron  vessels. 

The  cold  produced  by  evaporation  has  been  already  adverted  to;  it  is 
simply  an  eflfect  arising  from  the  conversion  of  sensible  heat  into  latent  by 
the  rising  vapour,  and  it  may  be  illustrated  in  a  variety  of  ways.  A  little 
ether  dropped  on  the  hand  thus  produces  the  sensation  of  great  cold,  and 
•water  contained  in  a  thin  glass  tube,  surrounded  by  a  bit  of  rag,  is  speedily 
frozen  when  the  rag  is  kept  wetted  with  ether. 


HEAT. 


65 


Fig.  42. 


When  a  little  water  is  put  into  a  watch-glass, 
(fig.  42),  supported  by  a  triangle  of  wire  over 
a  shallow  glass  dish  of  sulphuric  acid  placed 
on  the  plate  of  a  good  air-pump,  the  whole 
covered  with  a  low  receiver,  and  the  air  with- 
drawn as  perfectly  as  possible,  the  water  is  in 
a  few  minutes  converted  into  a  solid  mass  of  ice, 
and  the  watch-glass  very  frequently  broken  by 
the  expansion  of  the  lower  portion  of  water  in 
the  act  of  freezing,  a  thick  crust  first  forming  on  the  surface.  The  absence 
of  the  impediment  of  the  air,  and  the  rapid  absorption  of  watery  vapour  by 
the  oil  of  vitriol,  induce  such  quick  evaporation  that  the  water  has  its  tem- 
perature almost  immediately  reduced  to  the  freezing-point. 

The  same  fact  is  shown  by  a  beautiful  instrument  contrived  by  Dr.  Wol- 
laston,  called  a  cryophorus,  or  frost-carrier.  It  is  made  of  glass,  of  the  form 
represented  in  fig.  43,  and  contains  a  small  quantity  of  water,  the  rest  of 
the  space  being  vacuous.  When  all  the  water  is  turned  into  the  bulb,  and 
the  empty  extremity  plunged  into  a  mixture  of  ice  and  salt,  the  solidification 
of  the  vapour  gives  rise  to  such  a  quick  evaporation  from  the  surface  of  the 
water,  that  the  latter  freezes. 

Fig.  43. 


Fig.  44. 


All  means  of  producing  artificial  cold  yield  to  that  derived  from  the 
poration  of  the  liquefied  carbonic  acid,  just  mentioned.  When  a  jet  of 
liquid  is  allowed  to  issue  into  the  air  from  a  nar- 
row aperture,  such  an  intense  degree  of  cold  is 
produced  by  the  vaporization  of  a  part,  that  the 
remainder  freezes  to  a  solid,  and  falls  in  a  shower 
of  snow.  By  sufl'ering  this  jet  of  liquid  to  flow  into 
a  metal  box  provided  for  the  purpose,  shown  in  the 
drawing  of  the  apparatus  (fig.  44),  a  large  quantity 
of  the  solid  acid  may  be  obtained ;  it  closely  re- 
sembles snow  in  appearance,  and  when  held  in  the 
hand  occasions  a  painful  sensation  of  cold,  while 
it  gradually  disappears.  Mixed  with  a  little  ether, 
and  poured  upon  a  mass  of  mercury,  the  latter 
is  almost  instantly  frozen,  and  in  this  way  pounds 
of  the  solidified  metal  may  be  obtained.  The  addi- 
tion of  the  ether  facilitates  the  contact  of  the  car- 
bonic acid  with  the  mercury. 

The  temperature  of  a  mixture  of  solid  carbonic 
acid  and  ether  in  the  air,  measured  by  a  spirit- 
thermometer,  was  found  to  be  — 10G°  ( — 76° -GC)  ; 
when  the  same  mixture  was  placed  Iseneath  the 
receiver  of  an  air-pump,  and  exhaustion  rapidly 
made,  the  temperature  sank  to  — 166°  ( — 110°C). 
This  was  the  method  of  obtaining  extreme  cold 
employed  by  Mr.  Faraday  in  his  last  experiments 
on  the  liquefaction  of  gases.  Under  such  circum- 
6* 


eva- 

that 


36  HEAT. 

stances,  the  liquefied  hydriodic,  hydrobromic,  and  sulphnrons  acid  gases, 
carbonic  acid,  nitrous  oxide,  sulphuretted  liydrogen,  cyanogen,  and  ammo 
nia,  froze  to  colourless  transparent  solids,  and  alcohol  became  thick  and  oily. 
The  principle  of  the  cryophorus  has  been  very  happily  applied  by  Mr. 
Daniell  to  the  construction  of  a  dew-point  hygrometer ;  fig.  44.  It  consists 
of  a  bent  glass  tube  terminated  by  two  bulbs,  one  of  which  is  half  filled  with 
ether,  the  whole  being  vacuous  as  respects  atmospheric  air.  A  delicate  ther- 
mometer is  contained  in  the  longer  limb,  the  bulb  of  which  dips  into  the 
ether ;  a  second  thermometer  on  the  stand  serves  to  show  the  actual  tempe- 
rature of  the  air.  The  upper  bulb  is  covered  with  a  bit  of  muslin.  When 
an  observation  is  to  be  made,  the  liquid  is  all  transferred  to  the  lower  bulb, 
and  ether  dropped  upon  the  upper  one,  until  by  the  cooling  effects  of  evapo- 
ration a  distillation  of  the  contained  liquid  takes  place  from  one  part  of  the 
apparatus  to  the  other,  by  which  such  a  reduction  of  temperature  of  the 
ether  is  brought  about,  that  dew  is  deposited  on  the  outside  of  the  bulb,  which 
is  made  of  black  glass  in  order  that  it  may  be  more  easily  seen.  The  differ- 
ence of  temperature  indicated  by  the  two  thermometers  is  then  read  off. 

CAPACITY   FOR   HEAT;    SPECIFIC    HEAT. 

Let  the  reader  renew  a  supposition  made  when  the  doctrine  of  latent  heat 
was  under  consideration;  let  him  imagine  the  existence  of  an  uniform  source 
of  heat,  and  its  intensity  such  as  to  raise  a  given  weight  of  water  10" 
(5° -50)  in  30  minutes.  If,  now,  the  experiment  be  repeated  with  equal 
weights  of  mercury  and  oil,  it  will  be  found,  that  instead  of  30  minutes,  1 
minute  will  suffice  in  the  former  case,  and  15  minutes  in  the  latter. 

This  experiment  serves  to  point  out  the  very  important  fact,  that  different 
bodies  have  different  capacities  for  heat ;  that  equal  weights  of  water,  oil, 
and  mercury,  require,  in  order  to  rise  through  the  same  range  of  tempera- 
ture, quantities  of  heat  in  proportion  of  the  numbers  30,  15,  and  1.  This 
is  often  expressed  by  saying  that  the  specific  heat  of  water  is  30  times  as 
great  as  that  of  mercury,  and  the  specific  heat  of  oil  15  times  as  great. 

Again,  if  equal  weights  of  water  at  100°  (37o-7C),  and  oil  at  40°  (4o-4C), 
be  agitated  together,  the  temperature  of  the  whole  will  be  found  to  be  80° 
(26° -GC),  instead  of  70°  (21°-1C),  the  mean  of  the  two  ;  and  if  the  tempera- 
tures be  reversed,  that  of  the  mixture  will  be  only  60°  (15° -SC).     Thus, 

1  lb.  Z^i  "*  '400  *(I°'4C)  }  8'™  "  ■"-'"■«  -'  8»°  (26-6C) ,  hence 
Loss  by  the  water,  20°  (11°-1C). 
Gain  by  the  oil,       40°  (22°-2C). 

\  lb."  TifaT  ''  lit  (l7°7C)  }  g^^^  ^  ^^^*^^*^  ^'  ^0°  (l^^-^C)  5  ^^^^'^ 
Gain  of  water,  20°  (11°-1C). 
Loss  of  oil,       40°  (22°-2C). 
This  shows  the  same  fact,  that  water  requires  twice  as  much  heat  as  oil  to 
produce  the  same  thermometric  effect. 

There  are  three  distinct  methods  by  which  the  specific  heat  of  various 
ubstances  may  be  estimated.  The  first  of  these  is  by  observing  the  quantity 
f  ice  melted  by  a  given  weight  of  the  substance  heated  to  a  particular  tem- 
perature ;  the  second  is  by  noting  the  time  which  the  heated  body  requires 
to  cool  down  through  a  certain  number  of  degrees ;  and  the  third  is  the 
method  of  mixture,  on  the  principle  illustrated ;  this  latter  method  is  pre- 
ferred as  the  most  accurate. 

The  determination  of  the  specific  heat  of  different  substances  has  occupied 
the  attention  of  many  experimenters ;  among  these  MM.  Dulong  and  Tetit, 
and  recently  M.  Regnault,  deserve  especial  mention.  It  appears  that  each 
Bolid  and  liquid  has  its  own  specific  heat ;  and  it  is  probable  that  this,  in- 


HEAT.  b  < 

Btead  of  being  a  constant  quantity,  varies  with  the  temperature.  The  de- 
termination of  the  specific  heat  of  gases  is  attended  with  peculiar  diflSculties 
on  account  of  the  comparatively  large  volume  of  small  weights  of  gases. 
Satisfactory  results  have  however  been  obtained  by  the  method  of  mixing  for 
the  following  gases. 

SPECIFIC    HEAT   AT   30   INCHES   PRESSURE. 
Of  equal  volumes.  Of  equal  weights. 

Air  =  1        Water  =  1 

Atmospheric  air 1    1  0-2669 

Oxygen 1 0-8848  0-2361 

Hydrogen 1   12-3401  3-2936 

Nitrogen 1    1-0318  0-2754 

Carbonic  oxide 1» 1-0805  0-2884 

Protoxide  of  Ditrogen ...  1-227   0-8878  0-2369 

Carbonic  acid 1-249  0-8280  0-2210 

defiant  gas 1-754  1-5763  0-4207 

Aqueous  vapour 1-960  3-1360  0-8470' 

For  the  comparison  of  the  specific  heat  of  atmospheric  air  with  that  of 
water,  we  are  indebted  to  Count  Rumford ;  for  the  comparison  of  the  specific 
heat  of  the  various  gases,  to  Delaroche  and  Berard. 

Whenever  a  gas  expands,  heat  becomes  thereby  latent.  Hence  the  amount 
of  heat  required  to  raise  a  gas  to  a  certain  temperature  increases  the  more 
we  allow  it  to  expand.  Dulong  has  found  that  if  the  amount  of  heat  re- 
quired to  raise  the  temperature  of  a  volume  of  gas  (observed  at  the  melting 
point  of  ice,  and  at  the  pressure  of  30  inches)  to  a  given  height  without  its 
volume  undergoing  any  change,  be  represented  by  1,  then  if  the  gas  is  al- 
lowed to  expand  until  the  pressure  is  reduced  again  to  30  inches  whilst  the 
high  temperature  is  kept  up,  the  additional  amount  of  heat  which  is  required 
for  this  purpose  is,  for  oxygen,  hydrogen,  or  nitrogen  0,421 ;  for  carbonic 
acid  0,423  ;  for  binoxide  of  nitrogen  0,343  ;  and  for  defiant  gas  0,240. 

If  there  be  no  source  of  heat  from  which  this  additional  quantity  can  be 
obtained,  then  the  gas  is  cooled  during  expansion,  a  portion  of  the  free  heat 
becoming  latent.  On  the  other  hand,  if  a  gas  be  compressed,  this  latent 
heat  becomes  free,  and  causes  an  elevation  of  temperature,  which,  under 
favourable  circumstances,  may  be  raised  to  ignition ;  syringes  by  which 
tinder  is  kindled  are  constructed  on  this  principle.  In  the  upper  regions  of 
the  atmosphere  the  cold  is  intense;  snow  covers  the  highest  mountain-tops 
even  within  the  tropics,  and  this  is  due  to  the  increased  capacity  for  heat  of 
the  expanded  air. 

MM.  Dulohg  and  Petit  observed  in  the  course  of  iheir  investigation  a  most 
remarkable  circumstance.  If  the  specific  heats  of  bodies  be  computed  upon 
equal  weights,  numbers  are  obtained,  all  difi"erent,  and  exhibiting  no  simple 
relations  among  themselves  ;  but  if,  instead  of  equal  weights,  quantities  bo 
taken  in  the  proportion  of  the  chemical  equivalents,  an  almost  perfect  coin- 
cidence in  the  numbers  will  be  observed,  showing  that  some  exceedingly  in- 
timate connexion  must  exist  between  the  relations  of  bodies  to  heat  and 
their  chemical  nature ;  and  when  the  circumstance  is  taken  into  view,  that 
relations  of  even  a  still  closer  kind  link  together  chemical  and  electrical 
phenomena,  it  is  not  too  much  to  expect  that  ere  long  some  law  may  be  dis- 
covered far  more  general  than  any  with  which  we  are  yet  acquainted. 

*  The  later  determinations  of  Regnault  vary  from  the  above:  thus  in  equal  •«reij5hti«, 
■Water  =  l;  Atmospheric  air  he  gives  a.s  0-2o77;  Oxyi^en,  .0-2182;  Nitrogen,  0-2440;  and 
Vapour  of  Water,  0-4750;  and  contrary  to  the  results  of  Gay-Lussac,  the  specific  heat  of  ttir 
does  not  vary  with  the  temperature.  —  R.  B. 


68  HEAT. 

The  following  table  is  extracted  from  the  memoirs  of  M.  Regnault,  witii 
whose  results  most  of  the  experiments  of  Dulong  and  Petit  closely  coincide 

Substances.  Specific  heat  of  Specific  heat  of 

equal  weights.  equivalent  weights. 

Water  1-00000 

Oil  of  Turpentine  0-42593 

Glass  0-19768 

Iron 011379  80928 

Zinc  009555  3-0872 

Copper t 0-09515  3-0172 

Lead  0-03140  3-2581 

Tin  0-05623  3-3121 

Nickel 0-10863  3-2176 

Cobalt 0-l«696  3-1628 

Platinum  003243  3-2054 

Sulphur 0-20259  3-2657 

Mercury 0-03332  3-7128 

Silver 0-05701  61742 

Arsenic  0-08140  6-1326 

Antimony 0-05077 6-5615 

Gold  0-03244  6-4623 

Iodine 0-05412  6-8462 

Bismuth  0-03084  2-1877 

Of  the  numbers  in  the  second  column,  the  first  ten  approximate  far  too 
closely  to  each  other  to  be  the  result  of  mere  accidental  coincidence  ;  the  five 
that  follow  are  very  nearly  twice  as  great;  and  the  last  is  one-third  less.' 

Independently  of  experimental  errors,  there  are  many  circumstances 
which  tend  to  show,  that,  if  all  modifying  causes  could  be  compensated,  or 
their  effects  allowed  for,  the  law  might  be  rigorously  true. 

The  observations  thus  made  upon  elementary  substances  have  been  ex- 
tended by  M.  Regnault  to  a  long  series  of  compounds,  and  the  same  curious 
law  found,  with  the  above  limitations,  to  prevail  throughout,  save  in  a  few 
isolated  cases,  of  which  an  explanation  can  perhaps  be  given. 

Except  in  the  case  of  certain  metallic  alloys,  where  the  specific  heats  were 
the  mean  of  those  of  their  constituent  metals,  no  obvious  relation  can  be 
traced  between  the  specific  heat  of  the  compound  body  and  of  its  compo- 
nents. The  most  general  expression  of  the  facts  that  can  be  given  is  the 
following : — 

In  bodies  of  similar  chemical  constitution,  the  specific  heats  are  in  an  inverse 
ratio  to  the  equivalent  weights,  or  to  a  multiple  or  submultiple  of  the  latter. — 
Simple  as  well  as  compound  bodies  will  be  comprehended  in  this  law.'* 

SOURCES    OF    HEAT. 

The  first  and  greatest  source  of  heat,  compared  with  which  all  others  are 
totally  insignificant,  is  the  sun.  The  luminous  rays  are  accompanied  by 
rays  of  a  heating  nature,  which,  striking  against  the  surface  of  the  earth, 
elevate  its  temperature ;  this  heat  is  communicated  to  the  air  by  convection, 
as  already  described,  air  and  gases  in  general  not  being  sensibly  heated  by 
the  passage  of  the  rays. 

'  The  equivalent  of  Bismuth  being  assumed  as  71,  but  adopting  213,  the  number  given 
under  the  head  of  bismuth,  the  specific  heat  of  an  equivalent  weight  will  be  6*5688,  or  coiu- 
■,'ido  with  the  five  preceding.  — R.  B. 

"  Ann.  Chim.  et  Phys.  Ixxiii.  5;  and  the  same,  3rd  series,  i.  129.  _  ^ 


HEAT.  6t7 

A  second"'source  of  heat  is  supposed  to  exist  in  the  interior  of  the  earth. 
It  has  been  observed,  that  in  sinking  mine-shafts,  boring  for  water,  &c.,  the 
temperature  rises  in  descending,  at  the  rate,  it  is  said,  of  about  1°  (|°C)  for 
every  45  feet,  or  117°  (65°C)  per  mile.  On  the  supposition  that  the  rise 
continued  at  the  same  rate,  at  the  depth  of  less  than  two  miles  the  earth 
would  have  the  temperature  of  boiling  water ;  at  nine  miles  it  would  be  red 
hot ;  and  at  30  or  40  miles  depth,  all  known  substances  would  be  in  a  state 
of  fusion.' 

According  to  this  idea,  the  earth  must  be  looked  upon  as  an  intensely- 
heated,  fluid  spheroid,  covered  with  a  crust  of  solid  badly-conducting  mat- 
ter, cooled  by  radiation  into  space,  and  bearing  somewhat  the  same  propor- 
tion in  thickness  to  the  ignited  liquid  within,  that  the  shell  of  an  egg  does 
to  its  fluid  contents.  Without  venturing  to  offer  any  opinion  on  this  theory, 
it  may  be  sufficient  to  observe  that  it  is  not  positively  at  variance  with  any 
known  fact ;  that  the  figure  of  the  el,rth  is  really  such  as  would  be  assumed 
by  a  fluid  mass ;  and,  lastly,  that  it  offers  the  best  explanation  we  have  of 
the  phenomena  of  hot  springs  and  volcanic  eruptions,  and  agrees  with  the 
chemical  nature  of  their  products. 

The  smaller,  and  what  may  be  called  secondary,  sources  of  heat,  are  very 
numerous;  they  may  be  divided,  for  the  present,  into  two  groups,  me- 
chanical motion  and  chemical  combination.  To  the  first  must  be  referred  ele- 
vation of  temperature  by  friction  and  blows ;  and  to  the  second,  the  effects  of 
combustion  and  animal  respiration.  With  regard  to  the  heat  developed  by 
friction,  it  appears  to  be  indefinite  in  amount,  and  principally  dependent 
upon  the  nature  of  the  rubbing  surfaces.  An  experiment  of  Count  Rumford 
is  on  record,  in  which  the  heat  developed  by  the  boring  of  a  brass  cannon 
was  sufficient  to  bring  to  the  boiling-point  two  and  a  half  gallons  of  water, 
while  the  dust  or  shavings  of  metal,  cut  by  the  borer,  weighed  a  few  ounces 
only.  Sir  H.  Davy  melted  two  pieces  of  ice  by  rubbing  them  together  in 
vacuo  at  32°  (0°C) ;  and  uncivilized  men,  in  various  parts  of  the  world,  have 
long  been  known  to  obtain  fire  by  rubbing  together  two  pieces  of  dry  wood. 
The  origin  of  the  heat  in  these  cases  is  by  no  means  intelligible. 

Malleable  metals,  as  iron  and  copper,  which  become  heated  by  hammering 
or  powerful  pressure,  are  found  thereby  to  have  their  density  sensibly 
increased  and  their  capacity  for  heat  diminished ;  the  rise  of  temperature  is 
thus  in  some  measure  explained.  A  soft  iron  nail  may  be  made  red-hot  by 
a  few  dexterous  blows  on  an  anvil ;  but  the  experiment  cannot  be  repeated 
until  the  metal  has  been  annealed^  and  in  that  manner  restored  to  its  original 
physical  state. 

The  disengagement  of  heat  in  the  act  of  combination  is  a  phenomenon  of 
the  utmost  generality.  The  quantity  of  heat  given  out  in  each  particular 
case  is  in  all  probability  fixed  and  definite  ;  its  intensity  is  dependent  upon 
the  time  over  which  the  action  is  extended.  Science  has  already  been  en- 
riched by  many  admirable,  although  yet  incomplete,  researches  on  this  im- 
portant but  most  difficult  subject. 


It  is  not  improbable  that  many  of  the  phenomena  of  heat,  classed  at  present 
under  different  heads,  may  hereafter  be  referred  to  one  common  cause, 
namely,  alterations  in  the  capacity  for  heat  of  the  same  body  under  different 

«  The  new  Artesian  well  at  Grenelle,  near  Paris,  has  a  depth  of  1794-5  English  feet :  it  is 
bored  through  the  chalk  basin  to  the  sand  beneath ;  the  work  occupied  seyen  years  and  two 
months.  The  temperature  of  the  water,  which  is  exceedingly  abundant,  is  820  (270-7C) ;  tha 
mean  temperature  of  Paris  is  51o  (10O-5C);  the  difference  is  31°  (170-2C),  which  gives  a  rat« 
of  about  1°  (|oC)  for  58  feet. 


70  HEAT. 

physical  conditions.  For  example,  the  definite  absorption  and  evolution  of 
sensible  heat  attending  change  of  state  may  be  simply  due  to  the  increased 
capacity  for  heat,  to  a  fixed  and  definite  amount,  of  the  liquid  over  the  solid, 
and  the  vapour  over  the  liquid.  The  experimental  proof  of  the  facts  is  yet 
generally  wanting ;  in  the  very  important  case  of  water,  however,  the  deci- 
dedly inferior  capacity  for  heat  of  ice  compared  with  that  of  liquid  water 
seems  fully  proved  from  experiments  on  record. 

The  heat  of  combination  might  perhaps,  in  like  manner,  be  traced  to  con- 
densation of  volume,  and  the  diminution  of  capacity  for  heat  which  almost 
invariably  attends  condensation.  The  proof  of  the  proposition  in  numerous 
cases  would  be  within  the  reach  of  comparatively  easy  experimental  inquiry, 


«     • 


LIGHT.  71 


LIGHT. 

The  subject  of  light  is  so  littie  connected  >rith  elementary  chemistry,  that 

very  slight  notice  of  some  of  the  most  important  points  will  suflfice. 

Two  views  have  been  entertained  respecting  the  nature  of  light.  Sir 
Isaac  Newton  imagined  that  luminous  bodies  emitted,  or  shot  out,  infinitely 
small  particles  in  straight  lines,  which,  by  penetrating  the  transparent  part 
of  the  eye  and  falling  upon  the  nervous  tissue,  produced  vision.  Other  phi- 
losophers drew  a  parallel  between  the  properties  of  light  and  those  of  sound, 
and  considered,  that  as  sound  is  certainly  the  effect  of  undulations,  or  little 
waves,  propagated  through  elastic  bodies  in  all  directions,  so  light  might  be 
nothing  more  than  the  consequence  of  similar  undulations  transmitted  with 
inconceivable  velocity  through  a  highly  elastic  medium,  of  excessive  tenuity, 
filling  all  space,  and  occupying  the  intervals  between  the  particles  of  mate- 
rial substances,  to  which  they  gave  the  name  of  ether.  The  wave-hypothesis 
of  light  is  at  present  most  in  favour,  as  it  serves  to  explain  certain  singular 
phenomena,  discovered  since  the  time  of  Newton,  with  greater  facility  than 
the  other. 

A  ray  of  light  emitted  from  a  luminous  body  proceeds  in  a  straight  line, 
and  with  extreme  velocity.  Certain  astronomical  observations  afford  the 
means  of  approximating  to  a  knowledge  of  this  velocity.  The  satellites  of 
Jupiter  revolve  about  the  planet  in  the  same  manner  as  the  moon  about  the 
earth,  and  the  time  required  by  each  satellite  for  the  purpose,  is  exactly 
known  from  its  periodical  entry  into  or  exit  from  the  shadow  of  the  planet. 
The  time  required  by  one  is  only  42  hours.  Romer,  the  astronomer,  at 
Copenhagen,  found  that  this  period  appeared  to  be  longer  when  the  earth,  in 
its  passage  round  the  sun,  was  most  distant  from  the  planet  Jupiter,  and, 
on  the  contrary,  he  observed  that  the  periodic  time  appeared  to  be  shorter 
when  the  earth  was  nearest  to  Jupiter.  The  difference,  though  very  small, 
for  a  single  revolution  of  the  satellite,  by  the  addition  of  many,  so  increases, 
during  the  passage  of  the  earth  from  its  nearest  to  its  greatest  distance 
from  Jupiter,  that  is,  in  about  half  a  year,  that  it  amounts  to  16  minutes 
and  16  seconds.  Romer  concluded  from  this,  that  the  light  of  the  sun 
reflected  from  the  satellite,  required  that  time  to  pass  through  a  distance 
equal  to  the  diameter  of  the  orbit  of  the  earth,  and  since  this  space  is  little 
short  of  200  millions  of  miles,  the  velocity  of  light  cannot  be  less  than  200,000 
miles  in  a  second  of  time.  It  will  be  seen  hereafter  that  this  rapidity  of 
transmission  is  rivalled  by  that  of  the  electrical  agent. 

When  a  ray  of  light  falls  on  a  plane  surface  it  may  be  disposed  of  m  three 
ways ;  it  may  be  absorbed  and  disappear  altogether ;  it  may  be  reflected,  or 
thrown  off,  according  to  a  particular  law ;  or  it  may  be  partly  absorbed, 
partly  reflected,  and  partly  transmitted.  The  first  happens  when  the  surface 
is  perfectly  black  and  destitute  of  lustre ;  the  second,  when  a  polished  surface 
of  any  kind  is  employed;  and  the  third,  when  the  body  upon  which  the  light 
falls  is  of  the  kind  called  transparent,  as  glass  or  water. 

The  law  of  reflection  is  extremely  simple.  If  a  line  be  drawn  perpendi- 
cular to  the  surface  upon  which  the  ray  falls,  and  the  angle  contained 
between  the  raj^  and  the  perpendicular  measured,  it  will  be  found  that  the 
ray,  after  reflection,  takes  such  a  course  as  to  make  with  the  perpendiculai 


•72 


LIGHT. 


Fig.  45. 


Fig.  46. 


an  equal  angle  on  the  opposite  of  the  latter.     A  ray  of  light,  r,  fig.  45, 

falling  at  the  point  r,  will  he  reflected  in 
the  direction  pr'',  making  the  angle  r-'pp^ 
equal  to  the  angle  rpp^  ;  or  a  ray  from 
the  point  r  falling  upon  the  same  spot  will 
be  reflected  to  r^  in  virtue  of  the  same 
law.  Farther,  it  is  to  be  observed,  that 
the  incident  and  reflected  rays  are  always 
contained  in  the  same  vertical  plane. 

The  same  rule  holds  good  if  the  mirror 
be  curved,  as  a  portion  of  a  sphere,  the 
curve  being  considered  as  made  up  of  a 
multitude  of  little  planes.  Parallel  rays 
become  permanently  altered  in  direction  when  reflected  from  curved  surfaces, 
becoming  divergent  or  convergent  according  to  the  kind  of  curvature. 

It  has  just  been  stated  that  light  passes  in  straight  lines ;  but  this  is  only 
^rue  so  long  as  the  medium  through  which  it  travels  preserves  the  same 
density  and  the  same  chemical  nature ;  when  this  ceases  to  be  the  case,  the 

ray  of  light  is  bent  from  its  course 
into  a  new  one,  or,  in  optical  lan- 
guage, is  said  to  be  refracted. 

Let  r,  fig.  46,  be  a  ray  of  light 
falling  upon  a  plate  of  some  trans- 
parent substance  with  parallel  sides, 
such  as  a  piece  of  thick  plate  glass ; 
and  a  its  point  of  contact  with  the 
upper  surface.  The  ray,  instead 
of  holding  a  straight  course  and 
passing  into  the  glass  in  the  direc- 
tion a  b,  will  be  bent  downwards 
to  c ;  and,  on  leaving  the  glass,  and  issuing  into  the  air  on  the  other  side, 
it  will  again  be  bent,  but  in  the  opposite  direction,  so  as  to  make  it  parallel 
to  the  continuation  of  its  former  track.  The  general  law  is  thus  expressed : 
— When  the  ray  passes  from  a  rare  to  a  denser  medium,  it  is  usually  refracted 
towards  a  line  perpendicular  to  the  surface  of  the  latter ;  and  conversely, 
when  it  leaves  a  dense  medium  for  a  rarer  one,  it  is  refracted  from  a  line 
perpendicular  to  the  surface  of  the  denser  substance :  in  the  former  case 
the  angle  of  incidence  is  said  to  be  greater  than  that  of  refraction ;  in  the 
latter,  it  is  said  to  be  less. 
The  amount  of  refraction,  for  the  same  medium,  varies  with  the  obliquity 
with  which  the  ray  strikes  the  surface.  When 
perpendicular  to  the  latter,  it  passes  without 
change  of  direction  at  all ;  and  in  other  posi- 
tions, the  refraction  increases  with  the  obli- 
quity. 

Let  R,  fig.  47,  represent  a  ray  of  light  fall- 
ing upon  the  surface  of  a  mass  of  plate  glass 
at  the  point  a.  From  this  point  let  a  perpen- 
dicular be  raised  and  continued  into  the  new 
medium,  and  around  the  same  point,  as  a 
centre,  let  a  circle  be  drawn.  According  to 
the  law  just  stated,  the  refraction  must  be  to- 
wards the  perpendicular ;  in  the  direction  ar^ 
for  example.  Let  the  lines  a — a,  a' — a^,  at 
right  angles  to  the  perpendicular,  be  drawn, 
and  their  length  compared  by  means  of  a  scale  of  equal  parts,  and  noted ; 


LIGHT. 


73 


their  length  will  be  in  the  case  supposed  in  the  proportion  of  3  to  2.  These 
lines  are  termed  the  sines  of  the  angles  of  incidence  and  refraction,  re- 
spectively. 

Now  let  another  ray  be  taken,  such  as  r  ;  it  is  refracted  in  the  same  man- 
ner to  r^,  the  bending  being  greater  from  the  increased  obliquity  of  the  ray ; 
but  what  is  very  remarkable,  if  the  sines  of  the  two  new  angles  of  inci- 
dence and  refraction  be  again  compared  they  will  still  be  found  to  bear  to 
each  other  the  proportion  of  8  to  2.  The  fact  is  expressed  by  saying,  that 
the  ratio  of  the  sinea  of  the  incidence  and  refraction  is  constant  for  the  same 
medium. 

The  plane  of  refraction  coincides  moreover  with  that  of  incidence. 

Different  bodies  possess  different  refractive  powers ;  generally  speaking, 
the  densest  substances  refract  most.  Combustible  bodies  have  been  noticed 
to  possess  greater  refractive  power  than  their  density  would  indicate,  and 
from  this  observation  Sir  I.  Newton  predicted  the  combustible  nature  of  the 
diamond  long  before  anything  was  known  respecting  its  chemical  nature. 

The  method  adopted  for  describing  the  comparative  refractive  powers  of 
different  bodies  is  to  state  the  ratio  borne  by  the  sine  of  the  angle  of  refrac- 
tion to  that  of  incidence,  making  the  former  unity :  this  is  called  the  i7idex 
of  refraction  for  the  substance.  Thus,  in  the  case  of  glass,  the  index  of  re- 
fraction will  be  1-5.  When  this  is  once  known  for  any  particular  transparent 
body,  the  effect  of  the  latter  upon  a  ray  of  light  entering  it,  in  any  position, 
can  be  calculated  by  the  aid  of  the  law  of  sines. 


Substances.  Index  of  refraction. 

Tabasheer' 110 

Ice 1-30 

Water 1-34 

Fluor  spar 1-40 

Plate  glass 1-60 

Rock  crystal 1-60 

Crysolite 1-69 

Bisulphide  of  carbon 1-70 


Substances.  Index  of  refraction. 

Garnet 1-80 

Glass,  with   much   oxide 

of  lead 1-90 

Zircon 200 

Phosphorus 2-20 

Diamond 2-50 

Chromate  of  lead 3  00 


Fig.  48. 


When  a  luminous  ray  enters  a  mass  of  substance  differing  in  refractive 
power  from  the  air,  and  whose  surfaces  are  not  parallel,  it  becomes  perma- 
nently deflected  from  its  course  and  altered  in  its 
direction.  It  is  upon  this  principle  that  the  pro- 
perties of  prisms  and  lenses  depend.  To  take 
an  example. — Let  fig.  48  represent  a  triangular 
prism  of  glass,  upon  the  side  of  which  the  ray 
of  light  B  may  be  supposed  to  fall.  This  ray 
will  of  course  be  refracted  in  entering  the  glass 
towards  a  line  perpendicular  to  the  first  surface, 
and  again,  from  a  line  perpendicular  to   the 

second  surface  on  emerging  into  the  air.     The  result  will  be  a  total  change 
in  the  direction  of  the  ray. 

A  convex  lens  is  thus  enabled  to  converge  rays  of  light  falling  upon  it, 
and  a  concave  lens  to  separate  them  more  widely ;  each  separate  part  of  the 
surface  of  the  lens  producing  its  own  independent  effect. 

The  light  of  the  sun  and  celestial  bodies  in  general,  as  well  as  that  of  +lie 
electric  spark,  and  of  all  ordinary  flames,  is  of  a  compound  nature.  If  a  ray 
of  light  from  any  of  the  sources  mentioned  be  admitted  into  a  dark  room  by  a 
small  hole  in  the  shutter,  or  otherwise  (fig.  49),  and  suffered  to  fall  upon  a 


A  siliceous  deposit  in  tlie  joints  of  the  bamboo. 


74 


glass  prism  in  the  manner  described  above,  it  will  not  only  be  refracted  from 
its  straight  course,  but  will  be  decomposed  into  a  number  of  coloured  rays, 
which  may  be  received  upon  a  white  screen  placed  behind  the  prism.  When 
solar  light  is  employed,  the  colours  are  extremely  brilliant,  and  spread  into 
an  oblong  space  of  considerable  length.  The  upper  part  of  this  image  or 
spectrum  will  be  violet,  and  the  lower  red,  the  intermediate  portion,  com- 
mencing from  the  violet,  being  indigo,  blue,  green,  yellow,  and  orange,  all 
graduating  imperceptibly  into  each  other.  This  is  the  celebrated  experiment 
of  Sir  I.  Newton,  and  from  it  he  drew  the  inference  that  white  light  is  com- 
posed of  seven  primitive  colours,  the  rays  of  which  are  differently  refran- 
gible by  the  same  medium,  and  hence  capable  of  being  thus  separated.  The 
violet  rays  are  most  refrangible,  and  the  red  rays  least. 

Sir  D.  Brewster  is  disposed  to  think,  that  out  of  Newton's  seven  primitive 
colours  four  are  really  compound,  and  formed  by  the  superposition  of  the 
three  remaining,  namely,  blue,  yellow,  and  red,  which  alone  deserve  the 
name  of  primitive.  When  these  three  kinds  of  rays  are  mixed,  or  super- 
imposed, in  a  certain  definite  manner,  they  produce  white  light,  but  when 
one  or  two  of  them  are  in  excess,  then  an  effect  of  colour  is  perceptible, 
simple  in  the  first  case,  and  compound  in  the  second.  There  are,  according 
to  this  hypothesis,  rays  of  all  refrangibilities  of  each  colour,  and  conse- 
quently white  light  in  every  part  of  the  spectrum,  but  then  they  are  une- 
qually distributed  ;  the  blue  rays  are  more  numerous  near  the  top,  the  yel- 
low towards  the  middle,  and  the  red  at  the  bottom,  the  excess  of  each  colour 
producing  its  characteristic  effect.  In  the  diagram  below  (fig.  50)  the  inten- 
sity of  each  colour  is  represented  by  the  height  of  a  curve,  and  the  effects 
of  mixture  will  be  intelligible  by  a  little  consideration. 


Fig.  50. 
YELLOW.   RED. 


SOLAE  SPECTRUM. 


Bodies  of  the  same  mean  refractive  power  do  not  always  equally  disperse 
or  spread  out  the  differently  coloured  rays;  because  the  principal  yellow  or 
red  rays,  for  instance,  are  equally  refracted  by  two  prisms  of  different  ma- 
terials, it  does  not  follow  that  the  blue  or  the  violet  shall  be  similarly 
affected.  Hence,  prisms  of  different  varieties  of  glass,  or  other  transparent 
substances,  give,  under  similar  circumstances,  very  different  spectra,  both 


LIGHT.  75 

as  respects  the  length  of  the  image,  and  the  relative  extent  of  the  coloured 
bands. 

The  colours  of  natural  objects  are  supposed  to  result  from  the  power 
which  the  surfaces  of  the  bodies  possess  of  absorbing  some  of  the  coloured 
rays,  while  they  reflect  or  transmit,  as  the  case  may  be,  the  remainder. 
Thus,  an  "object  appears  red  because  it  absorbs,  or  causes  to  disappear,  a 
portion  of  the  yellow  and  blue  rays  composing  the  white  light  by  which  it  is 
illuminated. 

A  ray  of  common  light  made  to  pass  through  certain  crystals  of  a  par- 
ticular order  is  found  to  undergo  a  very  remarkable  change.  It  becomes 
split  or  divided  into  two  rays,  one  of  which  follows  the  general  law  of  refrac- 
tion, and  the  other  takes  a  new  and  extraordinary  course,  dependent  on  the 
position  of  the  crystal.  This  effect,  which  is  called  double  refraction,  is 
beautifully  illustrated  in  the  case  of  Iceland  spar,  or  crystallized  carbonate 
of  lime.  On  placing  a  rhomb  of  this  substance  on  a  piece  of  white  paper, 
on  which  a  mark  or  line  has  been  made,  the  object  will  be  seen  double. 

Again,  if  a  ray  of  light  be  suffered  to  fall  upon  a  plate  of  glass  at  an  angle 
of  56°  45',  the  portion  of  the  ray  which  suffers  reflection  will  be  found  to 
have  acquired  properties  which  it  did  not  before  possess ;  for  on  throwing 
it,  under  the  same  angle,  upon  a  second  glass  plate,  it  will  be  observed  that 
there  are  two  particular  positions  of  the  latter  in  which  the  ray  ceases  to 
be  reflected.     Light  which  has  suffered  this  change  is  said  to  he  polarized. 

The  light  which  passes  through  the  first  or  polarizing 
plate,  is  also  to  a  certain  extent  in  this  peculiar  condi-  Fig.  51. 

tion,  and  by  employing  a  series  of  similar  plates  (fig.  51),  R 

held  parallel  to  the  first,  this  effect  may  be  greatly  in-  \ 

creased ;  a  bundle  of  fifteen  or  twenty  such  plates  may  \ 

be  used  with  great  convenience  for  the  experiment.     It  is  \ 

to  be  remarked,  also,  that  the  light  polarized  by  trnn- 
mission  in  this  manner  is  in  an  opposite  state  to  tli: 
polarized   by  reflection ;    that   is,  when   examined   by  :i    '•, 
second  or  analyzing  plate,  held  at  the  angle  before  men-    ^ 
tioned,  it  will  be  seen  to  be  reflected  when  the  other  dis- 
appears, and  to  be  absorbed  when  the  first  is  reflected. 

It  is  not  every  substance  which  is  capable  of  polarizing 
light  in  this  manner ;  glass,  water,  and  certain  other  bo- 
dies, bring  about  the  change  in  question,  each  having  a 
particular  polarizing  angle  at  which  the  effect  is  greatest.  The  metals  also 
can,  by  reflection,  polarize  the  light,  but  they  do  so  very  imperfectly.  The 
two  rays  into  which  a  pencil  of  common  light  divides  itself  in  passing 
through  a  doubly-refracting  crystal  are  found  on  examination  to  be  polarized 
in  a  very  complete  manner,  and  also  transversely,  the  one  being  capable  of 
reflection  when  the  other  vanishes.  It  is  said  that  both  rays  are  polarized 
in  opposite  directions.  With  a  rhomb  of  transparent  Iceland  spar  of  toler- 
ably large  dimensions  the  two  oppositely-polarized  rays  may  be  widely  sepa- 
rated and  examined  apart. 

There  is  yet  another  method  of  polarization,  by  the  employment  of  plates 
of  the  mineral  tourmaline  cut  parallel  to  the  axis  of  the  crystal.  This  body 
polarizes  by  simple  transmission,  the  ray  falling  perpendicular  to  its  surface  ; 
a  part  of  the  light  is  absorbed,  and  the  remainder  modified  in  the  mannei 
described.  When  two  such  plates  are  held  with  their  axes  parallel,  as  in 
fig.  52,  light  traverses  them  both  freely ;  but  when  one  of  them  is  turned 
round  in  the  manner  shown  in  fig.  53,  so  as  to  make  the  axes  cross  at  right 
angles,  the  light  is  almost  wholly  stopped,  if  the  tourmalines  be  good.  A 
plate  of  the  mineral  thus  becomes  an  excellent  test  for  discriminating  be- 
tween the  polarized  light  and  that  which  has  not  undergone  the  change. 
Some  of  the  most  splendid  phenomena  of  the  science  of  light  are  exhibited 


76 


LIGHT 


Fig.  52. 


•when  thin  plates  of  doubly-refraoting  substances  are  interposed  between  the 
polarizing  arrangement  and  the  analyzer. 

Instead  of  the  tourmaline  plate,  which  is  always  coloured,  frequent  use 
is  made  of  two  Nichol's  prisms,  or  conjoined  prisms  of  carbonate  of  lime, 
which,  in  consequence  of  a  peculiar  cutting  and  combination,  possfiss  the 
property  of  allowing  only  one  of  the  oppositely  polarized  rays  to  pass.  If 
the  two  Nichol's  prisms  are  placed  one  behind  the  other  in  precisely  similar 
positions,  the  light  polarized  by  the  one  goes  through  the  other  unaltered. 
But  when  one  prism  is  slightly  turned  round  in  its  setting,  a  cloudiness  is 
produced,  and  by  continuing  to  turn  the  prism  this  increases  until  perfect 
darkness  ensues.  This  happens,  as  with  the  tourmaline  plates,  when  the 
two  prisms  cross  one  another.  The  phenomenon  is  the  same  with  colourless 
as  with  coloured  light. 

Supposing  that  polarized  light,  coloured,  for  example,  by  going  through  a 
plate  of  red  glass,  passed  through  the  first  Nichol's  prism  and  was  altogether ' 
obstructed  in  consequence  of  the  position  of  the  second  prism,  then  if  be- 
tween the  two  prisms  a  plate  of  rock  crystal,  formed  by  a  section  at  right 
angles  to  the  principal  axis  of  the  crystal,  is  interposed,  the  light  polarized 
by  the  first  prism  by  passing  through  the  plate  of  quartz  is  enabled  par- 
tially to  pass  through  the  second  Nichol's  prism.  Its  passage  through  the 
second  prism  can  then  again  be  interrupted  by  turning  the  second  prism 
round  to  a  certain  extent.  The  rotation  required  varies  with  the  thickness 
of  the  plate  of  rock  crystal,  and  also  with  the  colour  of  the  light  that  is 
employed.  It  increases  from  red  in  the  following  order,  green,  yellow,  blue, 
violet. 

This  property  of  rock  crystal  was  discovered  by  Arago.  The  kind,  of 
polarization  has  been  called  circular  polarization.  No  other  crystals  are 
known  to  produce  the  same  effect.  The  direction  of  the  rotation  is  with 
many  plates  towards  the  right  hand  ;  in  other  plates  it  is  towards  the  left. 
The  one  class  is  said  to  possess  right-handed  polarization ;  the  other  class 
left-lianded  polarization. 

Biot  observed  that  many  solutions  of  organic  substances  exhibit  the  pro- 
perty of  circular  polarization,  though  to  a  far  less  extent  than  rock  crystal. 
Thus,  solution  of  cane-sugar  and  tartaric  acid  possess  right-handed  polari- 
zation, whilst  albumen,  grape-sugar,  and  oil  of  turpentine,  are  left-handed. 
In  all  these  solutions  the  amount  of  circular  polarization  increases  with  the 
concentration  of  the  fluid  and  the  thickness  of  the  column  of  liquid  through 
which  the  light  passes.  Hence  circular  polarization  is  an  important  auxiliary 
in  chemical  analysis.  In  order  to  determine  the  amount  of  polarization 
which  any  fluid  exhibits,  the  liquid  is  put  into  a  glass  tube  not  less  than 
from  ten  to  twelve  inches  long,  whicl\^  is  closed  with  glass  plates,  one  of 
which  should  be  coloured,  red  for  example.  This  is  then  placed  between 
the  two  Nichol's  prisms,  which  have  previously  been  so  arranged  with  regard 
to  each  other  that  no  light  could  pass  through.  An  apparatus  of  this  de- 
scription, the  saccharometer,  is  chiefly  used  for  determining  the  concentra- 
tion of  solutions  of  sugar. 


Lia^T.  7? 

Faraday  has  made  the  remarkable  discovery,  that  if  a  very  strong  electric 
current  is  passed  round  a  substance  which  possesses  the  property  of  circular 
polarization,  the  amount  of  rotation  is  altered  to  a  considerable  degree. 

The  luminous  rays  of  the  sun  are  accompanied,  as  already  mentioned,  by 
others  which  possess  heating  powers.  If  the  temperature  of  the  different 
coloured  spaces  in  the  spectrum  be  tried  with  a  delicate  thermometer,  it 
will  be  found  to  increase  from  the  violet  to  the  red  extremity,  and  when  the 
prism  is  of  some  particular  kinds  of  glass,  the  greatest  effect  will  be  mani- 
fest a  little  beyond  the  visible  red  ray.  It  is  inferred  from  this  that  the 
chief  mass  of  the  heating  rays  of  the  sun  are  among  the  least  refrangible 
components  of  the  solar  beam. 

Again,  it  has  long  been  known  that  chemical  changes  both  of  combination 
and  of  decomposition,  but  more  particularly  the  latter,  could  be  effected  by 
the  action  of  light.  Chlorine  and  hydrogen  combine  at  common  tempera- 
lures  only  under  the  influence  of  light,  and  parallel  cases  occur  in  great 
numbers  in  organic  chemistry :  the  blackening  and  decomposition  of  salts 
of  silver  are  familiar  instances  of  the  chemical  powers  of  the  same  agent. 
Now  it  is  not  the  luminous  part  of  the  ray  which  effects  these  changes ;  they 
are  produced  by  certain  invisible  rays  accompanying  the  others,  and  which 
are  found  most  abundantly  in  and  beyond  the  violet  part  of  the  spectrum. 
It  is  there  that  the  chemical  effects  are  most  marked,  although  the  intensity 
of  the  light  is  exceedingly  feeble.  The  chemical  rays  are  thus  directly  op- 
posed to  the  heating  rays  in  the  common  spectrum  in  their  degree  of  refran- 
gibility,  since  they  exceed  all  the  others  in  this  respect. 

In  the  year  1802,*  Mr.  Thomas  Wedgwood  proposed  a  method  of  copying 
paintings  on  glass  by  placing  behind  them  white  paper  or  leather  moistened 
with  a  solution  of  nitrate  of  silver,  which  became  decomposed  and  blackened 
by  the  transmitted  light  in  proportion  to  the  intensity  of  the  latter;  and 
Davy,  in  repeating  these  experiments,  found  that  he  could  thus  obtain  tole- 
rably accurate  representations  of  objects  of  a  texture  partly  opaque  and 
partly  transparent,  such  as  leaves  and  the  wings  of  insects,  and  even  copy 
with  a  certain  degree  of  success  the  images  of  small  objects  obtained  by  the 
solar  microscope.  These  pictures,  however,  required  to  be  kept  in  the  dark, 
and  only  examined  by  candle-light,  otherwise  they  became  obliterated  by 
the  blackening  of  the  whole  surface  from  which  the  salt  of  silver  could  not 
be  removed.  These  attempts  at  light-painting  attracted  but  little  notice  till 
the  publication  of  Mr. 'Fox  Talbot's'^  papers,  read  before  the  Royal  Society, 
in  January  and  February,  1839,  in  which  he  detailed  two  methods  of  fixing 
the  pictures  produced  by  the  action  of  light  on  paper  impregnated  with 
chloride  of  silver,  and  at  the  same  time  described  a  plan  by  which  the  sen- 
sibility of  the  prepared  paper  may  be  increased  to  the  extent  required  for 
receiving  impressions  from  the  images  of  the  camera  obscura. 

Very  shortly  afterwards.  Sir  John  Herschel^  proposed  to  employ  solutions 
of  the  alkaline  hyposulphites  for  removing  the  excess  of  chloride  of  silver 
from  the  paper,  and  thus  preventing  the  farther  action  of  light,  and  this 
plan  has  been  found  exceedingly  successful.  The  greatest  improvement, 
however,  which  the  curious  art  of  photogenic  drawing  has  received,  is  due 
to  Mr.  Talbot,*  who,  in  a  communication  to  the  Royal  Society,  described  a 
method  by  which  paper  of  such  sensibility  could  be  prepared  as  to  permit 
its  application  to  the  taking  of  portraits  of  living  persons  by  the  aid  of  a 
good  camera  obscura,  the  time  required  for  a  perfect  impression  never  ex- 
ceeding a  few  minutes.  The  portraits  executed  in  this  manner  by  Mr. 
Collen  and  others  are  beautiful  in  the  highest  degree,  and  leave  little  room 
for  improvement  in  any  respect.     The  process  itself  is  rather  complex,  and 

»  Journal  of  the  Royal  Institution,  i.  170.  a  Phil.  Mag.  March,  1839 

»  Phil.  Trans,  for  1840,  p.  1.  *  phil.  Mag.  August.  1841. 

7  * 


78  LIGHT. 

demands  a  great  number  of  minute  precautions,  only  to  be  learned  by  expe- 
rience, but  which  are  indispensable  to  perfect  success.  The  general  plan  is 
the  following: — 

Writing-paper  of  good  quality  is  washed  on  one  side  with  a  moderately 
dilute  solution  of  nitrate  of  silver,  and  left  to  dry  spontaneously  in  a  dark 
room ;  when  dry,  it  is  dipped  into  a  solution  of  iodide  of  potassium,  and 
again  dried.  These  operations  should  be  performed  by  candle-light.  When 
required  for  use,  the  paper  thus  coated  with  yellow  iodide  of  silver  is  brushed 
over  with  a  solution  containing  nitrate  of  silver,  acetic  acid,  and  gallic  acid, 
and  once  more  carefully  dried  by  gentle  warmth.  This  kalotype  paper  is  so 
sensitive,  that  exposure  to  diffused  daylight  for  one  second  suffices  to  make 
an  impression  upon  it,  and  even  the  light  of  the  moon  produces  the  same 
effect,  although  a  much  longer  time  is  required. 

The  images  of  the  camera  obscura  are  at  first  invisible,  but  are  made  to 
appear  in  full  intensity  by  once  more  washing  the  paper  with  the  above 
mentioned  mixture,  and  warming  it  before  the  fire,  when  the  blackening 
effect  commences  and  reaches  its  maximum  in  a  few  minutes. 

The  picture  is  of  course  negative,  the  lights  and  shadows  being  reversed ; 
to  obtain  positive  copies  nothing  more  is  necessary  than  to  place  a  piece  of 
ordinary  photographic  paper  prepared  with  chloride  of  silver  beneath  the 
.kalotype  impression,  cover  them  with  a  glass  plate,  and  expose  the  whole  to 
the  light  of  the  sun  for  a  short  time.  Before  this  can  be  done,  the  kalotype 
must  however  be  fixed,  otherwise  it  will  blacken,  and  this  is  effected  by  im- 
mersion in  a  solution  of  hyposulphite  of  soda,  and  well  washing  with  water. 

Sir  John  Herschel  has  shown  that  a  great  number  of  other  substances  can 
be  employed  in  these  photographic  processes  by  taking  advantage  of  the 
singular  deoxidizing  effects  of  certain  portions  of  the  solar  rays.  Paper 
washed  with  a  solution  of  a  salt  of  sesquioxide  of  iron  becomes  capable  of 
receiving  impressions  of  this  kind,  which  may  afterwards  be  made  evident 
by  ferricyanide  of  potassium,  or  terchloride  of  gold.  Vegetable  colours  are 
also  acted  upon  in  a  very  curious  and  apparently  definite  manner  by  the 
different  parts  of  the  spectrum.' 

The  Daguerreotype,  the  announcement  of  which  was  first  made  in  the 
summer  of  1889  by  M.  Daguerre,  who  had  been  occupied  with  this  subject 
from  1826,  if  not  earlier,  is  another  remarkable  instance  of  the  decomposing 
effects  of  the  solar  rays.  A  clean  and  highly-polished  plate  of  silvered 
copper  is  exposed  for  a  certain  period  to  the  vapour  of  iodine,  and  then 
transported  to  the  camera  obscura.  In  the  most  improved  state  of  the  pro- 
cess, a  very  short  time  suffices  for  effecting  the  necessary  change  in  the  film 
of  iodide  of  silver.  The  picture,  however,  only  becomes  visible  by  exposing 
it  to  the  vapour  of  mercury,  which  attaches  itself,  in  the  form  of  exceed- 
ingly minute  globules,  to  those  parts  which  have  been  most  acted  upon,  that 
is  to  say,  to  the  lights,  the  shadows  being  formed  by  the  dark  polish  of  the 
metallic  plate.  Lastly,  the  drawing  is  washed  with  a  solution  of  hyposul- 
phite of  soda  to  remove  the  undecomposed  iodide  of  silver,  and  render  it 
permanent. 

The  images  of  objects  thus  produced  bear  the  most  minute  examination  with 
a  magnifying  glass,  the  smallest  details  being  depicted  with  perfect  fidelity. 

Great  improvements  have  been  necessarily  made  in  the  application  of  this 
beautiful  art  to  taking  portraits.  By  the  joint  use  of  bromine  and  iodine 
the  plates  are  rendered  far  more  sensitive,  and  the  time  of  sitting  is  short- 
ened to  a  very  few  seconds.  When  the  operation  is  completed  the  colour  of 
the  plate  is  much  improved  by  the  deposition  of  an  exceedingly  thin  film  of 
geld,  wliich  communicates  a  warm  purplish  tint,  and  removes  the  previous 
dull  leaden-grey  hue,  to  most  persons  very  offensive. 

'  Phil.  Trans.  1842,  p.  1, 


RADIATION    OP    HEAT.  79 


RADIATION,  REFLECTION,  ABSORPTION,  AND  TRANSMISSION 
OF  HEAT. 


RADIATION    OF   HEAT. 


If  a  red-hot  ball  be  placed  upon  a  metallic  support,  and  left  to  itself, 
cooling  immediately  commences,  and  only  stops  when  the  temperature  of  the 
ball  is  reduced  to  that  of  the  surrounding  air.  This  effect  takes  place  in 
three  ways :  heat  is  conducted  away  from  the  ball  through  the  substance  of 
the  support ;  another  portion  is  removed  by  the  convective  power  of  the  air ; 
and  the  residue  is  thrown  off  from  the  heated  body  in  straight  lines  or  rays, 
which  pass  through  air  without  interi'uption,  and  become  absorbed  by  the 
surfaces  of  neighbouring  objects  which  happen  to  be  presented  to  their 
impact. 

This  radiant  or  radiated  heat  resembles,  in  very  many  respects,  ordinary 
light ;  it  suffers  reflection  from  polished  surfaces  according  to  the  same  law ; 
it  is  absorbed  by  those  that  are  dull  or  rough ;  it  moves  with  extreme  velo- 
city ;  and,  finally,  it  traverses  certain  transparent  media,  undergoing  refrac- 
tion at  the  same  time,  in  obedience  to  the  laws  which  regulate  that  pheno- 
menon in  optics. 

The  fact  of  the  reflection  of  heat  may  be  very  easily  proved.  If  a  person 
stand  before  a  fire  in  such  a  position  that  his  face  may  be  screened  by  the 
mantelshelf,  and  if  he  then  take  a  bright  piece  of  metal,  as  a  sheet  of  tinned 
plate,  and  hold  it  in  such  a  manner  that  the  fire  may  be  seen  by  reflection, 
at  the  same  moment  a  distinct  sensation  of  heat  will  be  felt. 

The  apparatus  best  fitted  for  studying  these  facts  consists  of  a  pair  of  con- 
cave metallic  mirrors  of  the  form  called  parabolic.     The  parabola  is  a  curve 
possessing  very  peculiar  properties,  one  of  the  most  prominent  being  the 
following :  —  A  tangent  drawn  to  any  part  of  the  curve 
makes  equal  angles  with  two  lines,  one  of  which  pro-  Fig.  54. 

ceeds  fi'om  the  point  where  the  tangent  touches  the 
curve  in  a  direction  parallel  to  what  is  called  the  axis 
of  the  parabola, « and  the  other  from  the  same  spot 
through  a  point  in  front  of  the  curve,  called  the  focus. 
It  results  from  this  that  parallel  rays,  either  of  light 
or  heat,  falling  upon  a  mirror  of  this  particular  curva- 
ture in  a  direction  parallel  to  the  axis  of  the  parabola, 
will  be  all  reflected  to  a  single  point  at  the  focus ;  and 
rays  diverging  from  this  focus,  and  impinging  upon  the 
mirror,  will,  after  reflection,  become  parallel  (fig.  54). 

If  two  such  mirrors  be  placed  opposite  to  each  other 
at  a  considerable  distance,  and  so  adjusted  that  their 
axes  shall  be  coincident,  and  a  hot  body  placed  in  the 
focus  of  the  one,  while  a  thermometer  occupies  that  of  the  other,  the  reflec- 
tion of  the  rays  of  heat  will  become  manifest  by  their  effect  upon  the  instru 
ment.  In  this  manner,  with  a  pair  of  by  no  means  very  perfect  mirrors,  18 
inches  in  diameter,  separated  by  an  interval  of  20  feet  or  more,  amadou  or 


80 


RADIATION    OP    HEAT. 


gunpowder  ma/  be  readily  fired  by  a  red-hot  ball  in  the  focus  of  the  oppo- 
site mirror  (fig.  55). 

Fig.  05. 


The  power  of  radiation  varies  exceedingly  with-  diflferent  bodies,  as  may 
be  easily  proved.  If  two  similar  vessels  of  equal  capacity  be  constructed 
of  thin  metal,  atid  the  surface  of  one  highly  polished,  while  that  of  the 
other  is  covered  with  lampblack,  and  both  filled  with  hot  water  of  the  same 
temperature,  and  their  rate  of  cooling  observed  from  time  to  time  with  a 
thermometer,  it  will  be  constantly  found  that  the  blackened  vessel  loses  heat 
much  faster  than  the  one  with  bright  surfaces ;  and  since  both  are  put  on  a 
footing  of  equality  in  other  respects,  this  difference,  which  will  often  amount 
to  many  degrees,  must  be  ascribed  to  the  superior  emissive  power  of  the  film 
of  soot. 

By  another  arrangement,  a  numerical  comparison  can  be  made  of  these 
difl^erences.  A  cubical  metallic  ves.sel  is  prepared,  each  of  whose  sides  is  in 
a  diff'erent  condition,  one  being  polished,  another  rough,  a  third  covered 
with  lampblack,  &c.  This  vessel  is  filled  with  water,  kept  constantly  at 
212°  (100°C)  by  a  small  steam-pipe.  Each  of  its  sides  is  then  presented  in 
succession  to  a  good  pai'abolic  mirror,  having  in  its  focus  one  of  the  bulbs 
of  the  differential  thermometer  before  described  (fig.  22),  the  bulb  itself 
being  blackened.  The  effect  produced  on  this  instrument  is  taken  as  a 
measure  of  the  comparative  radiating  powers  of  the  different  surfaces. 
The  late  Sir  John  Leslie  obtained  by  this  method  of  experiment  the  follow- 
ing results :  — 


Emissive  power. 

Lampblack 100 

Writing-paper 98 

Glass 90 

Plumbago 75 


EmissiTe  power. 

Tarnished  lead 45 

Clean  lead 19 

Polished  iron 15 

Polished  silver 12 


The  best  reflecting  surfaces  are  always  the  worst  radiators ;  polished 
metal  reflects  nearly  all  the  heat  that  falls  upon  it,  while  its  radiating  power 
is  the  feeblest  of  any  substance  tried,  and  lampblack,  which  reflects  nothing, 
radiates  most  perfectly. 

The  power  of  absorbing  heat  is  in  direct  proportion  to  the  power  of  emis- 
sion. The  polished  metal  mirror,  in  the  experiment  with  the  red-hot  ball, 
remains  quite  cold,  although  only  a  few  inches  from  the  latter ;  or,  again, 
if  a  piece  of  gold  leaf  be  laid  upon  paper,  and  a  heated  iron  held  over  it 


•  The  formerly  supposed  influence  of  mere  diflFerence  of  surface  has  been  called  in  question 
t)y  M.  Melloni,  who  attributes  to  other  causes  the  eflfects  observed  by  Sir  John  Leslie  and 
others,  among  which  superficial  oxidation  and  difference  of  physical  condition  with  respect 
to  hardness  and  density,  are  among;  the  most  important.  With  metals  not  subject  to  tarnish, 
Bcratching  the  surface  increases  the  emissive  power  when  the  plates  have  been  rolled  or 
hammered,  i.  e.  are  in  a  compressed  state,  and  diminishes  it,  on  the  contrary,  when  the 
metal  has  been  cast  and  carefully  polished  without  burnishing.  In  the  case  of  ivory, 
marble,  and  jet,  where  compression  cannot  take  place,  no  difference  is  perceptible  in  the 
wuiiating  power  of  polished  and  rough  surfaces.  —  Ann.  Chim.  et  Phys.  Ixx.  435. 


RADIATION    OP    HEaT.  81 

until  the  paper  is  completely  scorched,  it  will  be  found  that  the  film  of  metal 
has  perfectly  defended  that  portion  beneath  it. 

The  faculty  of  absorption  seems  to  be  a  good  deal  influenced  by  colour ; 
Dr.  Franklin  found  that  when  pieces  of  cloth  of  various  colours  were  placed 
on  snow  exposed  to  the  feeble  sunshine  of  winter,  the  snow  beneath  them 
became  unequally  melted,  the  efl'ect  being  always  in  proportion  to  the  depth 
of  the  colour ;  and  Dr.  Stark  has  since  obtained  a  similar  result  by  a  dif- 
ferent method  of  experimenting.  According  to  the  late  researches  of  Mel- 
loni,  this  effect  depends  less  on  the  colour  than  on  the  nature  of  the  colour- 
ing matter  which  covers  the  surface  of  the  cloth. 

These  facts  afi'ord  an  explanation  of  two  very  interesting  and  important 
natural  phenomena,  namely,  the  origin  of  dew,  and  the  cause  of  the  land 
and  sea-breezes  of  tropical  countries.  While  the  sun  remains  above  the 
horizon,  the  heat  radiated  by  the  surface  of  the  earth  into  space  is  compen- 
sated by  the  absorption  of  the  solar  beams ;  but  when  the  sun  sets,  and  this 
supply  ceases,  while  the  emission  of  heat  goes  on  as  actively  as  before,  the 
surface  becomes  cooled  until  its  temperature  sinks  below  that  of  the  air. 
The  air  in  contact  with  the  earth  of  course  participates  in  this  reduction  of 
temperature ;  the  aqueous  vapour  present  speedily  reaches  its  point  of  max- 
imum density,  and  then  begins  to  deposit  moisture,  whose  quantity  will  de- 
pend upon  the  proportion  of  vapour  in  the  atmosphere,  and  on  the  extent  to 
which  the  cooling  process  has  been  carried. 

It  is  observed  that  dew  is  most  abimdant  in  a  clear  calm  night,  succeeding 
a  hot  day ;  under  these  circumstances  the  quantity  of  vapour  in  the  air  is 
usually  very  great,  and  at  the  same  time,  radiation  proceeds  with  most 
facility.  At  such  times  a  thermometer  laid  on  the  ground  will,  after  some 
time,  indicate  a  temperature  of  10°  (5°-5C),  15°  (8°-3C),  or  even  20°  (11°'1C) 
below  that  of  the  air  a  few  feet  higher.  Clouds  hinder  the  formation  of  dew, 
by  reflecting  back  to  the  earth  the  heat  radiated  from  its  surface,  and  thus 
preventing  the  necessary  reduction  of  temperature ;  and  the  same  effect  is 
produced  by  a  screen  of  the  thinnest  material  stretched  at  a  little  height 
above  the  ground.  In  this  manner  gardeners  often  preserve  delicate  plants 
from  destruction  by  the  frosts  of  spring  and  autumn.  The  piercing  cold  felt 
just  before  and  at  sunrise,  even  in  the  height  of  summer,  is  the  consequence 
of  this  refrigeration  having  reached  its  maximum. 

Wind  also  effectually  prevents  the  deposition  of  dew,  by  constantly  renew- 
ing the  air  lying  upon  the  earth  before  it  has  had  its  temperature  sufficiently 
reduced  to  cause  condensation  of  moisture. 

Many  curious  experiments  may  be  made  by  exposing  on  the  ground  at 
night,  bodies  which  differ  in  their  powers  of  radiation.  If  a  piece  of  black 
cloth  and  a  plate  of  bright  metal  be  thus  treated,  the  former  will  often  be 
found  in  the  morning  covered  with  dew,  while  the  latter  remains  dry. 

Land  and  sea-breezes  are  certain  periodical  winds  common  to  most  sea- 
coasts  within  the  tropics,  but  by  no  means  confined  to  those  regions.  It  is 
observed,  that  a  few  hours  after  sunrise  a  breeze  springs  up  at  sea,  and  blows 
directly  on  shore,  and  that  its  intensity  increases  as  the  day  advances,  and 
declines  and  gradually  expires  near  sunset.  Shortly  after,  a  wind  arises  in 
exactly  the  opposite  direction,  namely,  from  the  land  towards  the  sea,  lasts 
the  whole  of  the  night,  and  only  ceases  with  the  reappearance  of  the  sun. 

It  is  easy  to  give  an  explanation  of  these  effects.  When  the  sun  shines 
at  once  upon  the  surface  of  the  earth  and  that  of  the  sea,  the  two  become 
unequally  heated  from  their  different  absorbing  power ;  the  land  becomes 
much  the  warmer.  The  air  over  the  heated  surface  of  the  ground,  being  ex- 
panded by  heat,  rises,  and  has  its  place  supplied  by  colder  air  flowing  from 
the  sea,  producing  the  sea-breeze.  When  the  sun  sets,  both  sea  and  land 
begin  to  cool  by  radiation;  the  rate  of  the  cooling  of  the  latter  will,  how- 


82  TRANSMISSION     0,P,    HEAT. 

ever,  far  exceed  that  of  the  former,  and  its  temperature  -will  rapidly  fall. 
The  air  above  becoming  cooled  and  condensed,  flows  outwards  in  obedience 
to  the  laws  of  fluid  pressure,  and  displaces  the  warmer  air  of  the  ocean.  In 
this  manner,  by  an  interchange  of  air  between  sea  and  land,  the  otherwise 
oppressive  heat  is  moderated,  to  the  great  advantage  of  those  who  inhabit 
such  localities.  The  land  and  sea-breezes  extend  to  a  small  distance  only 
from  shore,  but  afford,  notwithstanding,  essential  aid  to  coasting  navigation, 
since  vessels  on  either  tack  enjoy  a  fair  wind  during  the  greater  part  of  both 
day  and  night. 

TRANSMISSION    OF   HEAT;    DIATHERMANCY. 

Bays  of  heat,  in  passing  through  air,  receive  no  more  obstruction  than 
those  of  light  under  similar  circumstances ;  but  with  other  transparent  media 
the  case  is  different.  If  a  parabolic  mirror  be  taken  and  its  axis  directed 
towards  the  sun,  the  rays  both  of  heat  and  light  will  be  reflected  to  the  focus, 
which  will  exhibit  a  temperature  sufficiently  high  to  fuse  a  piece  of  metal, 
or  fire  a  combustible  body.  If  a  plate  of  glass  be  now  placed  between  the 
mirror  and  the  sun,  the  effect  will  be  but  little  diminished. 

Now,  let  the  same  experiment  be  made  with  the  heat  of  a  kettle  filled  with 
boiling  water ;  the  heat  will  be  concentrated  by  reflection  as  before,  but,  on 
interposing  the  glass,  the  heating  effect  at  the  focus  will  be  reduced  to 
nothing.     Thus,  the  rays  of  heat  coming  from  the  sun  traverse  glass  with 
facility,  which  is  not  the  case  with  those  emanating  from  the  boiling  water. 
In  the  year  1833,  M.  Melloni  published  the  first  of  a  series  of  exceedingly 
valuable  researches  on  this  subject,  which  are  to  be  found  in  detail  in  various 
volumes  of  the  Annales  de  Chemie  et  de  Physique.*  It  will  be  necessary,  in  the 
f  iTst  instance,  to  describe  the  method  of  operation  followed  by  this  philosopher. 
Not  long  before,  two  very  remarkable  facts  had  been 
Fig.  56.  discovered :    Oersted,  in  Copenhagen,  showed  that  a 

current  of  electricity,  however  produced,  exercises  a 
singular  and  perfectly  definite  action  on  a  magnetic 
needle ;  and  Seebeck,  in  Berlin,  found  that  an  electric 
current  may  be  generated  by  the  unequal  effects  of  heat 
on  different  metals  in  contact.     If  a  wire  conveying  an 
electrical  current  be  brought  near  a  magnetic  needle, 
the  latter  will  immediately  alter  its  position  and  assume 
a  new  one,  as  nearly  perpendicular  to  the  wire  as  the 
mode  of  suspension  and  the  magnetism  of  the  earth 
will  permit.     When  the  wire,  for  example,  is  placed 
directly  over  the  needle  (fig.  56),  while  the  current  it  carries  travels  from 
north  to  south,  the  needle  is  deflected  from  its  ordinary  direction  and  the 
north  pole  driven  to  the  eastward.     When  the  current  is  reversed,  the  same 
pole  deviates  to  an  equal  amount  towards  the  west.     Placing  the  wire  below 
the  needle  instead  of  above  produces  tlie  same  effect  as  reversing  the  current. 
When  the  needle  is  subjected  to  the  action  of  two  currents  in  opposite 
directions,  the  one  above  and  the  other  below, 
Fig.  57.  they  will   obviously   concur   in    their   effects. 

The  same  thing  happens  when  the  wire  carry- 
ing the  current  is  bent  upon  itself  (fig.  57), 
and  the  needle  placed  between  the  two  por- 
tions ;  and  since  every  time  the  bending  is  re- 
peated, a  fresh  portion  of  the  current  is  made 
to  act  in  the  same  manner  upon  the  needle,  it 
is  easy  to  see  how  a  current  too  feeble  to  pro- 
duce any  effect  when  a  simple  straight  wire  is 

•  Translated  also  in  Tayloi's  Scientific  Memoirs. 


TRANSMISSION    OF    H  !£  *A'^  . 


83 


Fig.  58. 


employed,  may  be  made  by  this  contrivance  to  exhibit  a  powerful  action  on 
the  magnet.  It  is  on  this  principle  that  instruments  called  galvanometers^ 
galvanoscopes,  or  multipliers,  are  constructed ;  they  serve,  not  only  to  indicate 
the  existence  of  electrical  currents,  but  to  show  by  the  effect  upon  the  needle 
the  direction  in  which  they  are  moving.  By  using  a  very  long  coil  of  wire, 
and  two  needles,  immovably  connected,  and  hung  by  a  fine  filament  of  silk, 
almost  any  degree  of  sensibility  may  be  communicated  to  the  apparatus. 

When  two  pieces  of  different  metals,  connected  together  at  each  end,  have 
one  of  their  joints  more  heated  than  the  other,  an  electric  current  is  imme- 
diately set  up.  Of  all  the  metals  tried,  bismuth  and  antimony  form  the 
most  powerful  combination.  A  single  pair  of  bars,  having  one  of  their  junc- 
tions heated  in  the  manner  shown  in  fig.  58,  can 
develop  a  current  strong  enough  to  deflect  a 
compass-needle  placed  within,  and,  by  ar- 
ranging a  number  in  a  series  and  heating  their 
alternate  ends,  the  intensity  of  the  current  may 
be  very  much  increased.  Such  an  arrangement 
is  called  a  thermo-electric  pile.  M.  Melloni 
constructed  a  thermo-electric  pile  of  this  kind, 
containing  fifty-five  slender  bars  of  bismuth 
and  antimony,  laid  side  by  side  and  soldered 
together  at  their  alternate  ends.  He  connected 
this  pile  with  an  exceedingly  delicate  multiplier, 
and  found  himself  in  the  possession  of  an  in- 
strument for  measuring  small  variations  of  temperature  far  surpassing  in 
delicacy  the  air-thermometer  in  its  most  sensitive  form,  and  having  great 
advantages  in  other  respects  over  that  instrument  when  employed  for  the 
purposes  to  which  he  devoted  it. 

The  substances  whose  powers  of  transmission  were  to  be  examined  were 
cut  into  plates  of  a  determinate  thickness,  and,  after  being  well  polished, 
arranged  in  succession  in  front  of  the  little  pile,  the  extremity  of  which  was 
blackened  to  promote  the  absorption  of  the  rays.     (Fig.  59.)     A  perforated 


Fig.  69. 


screen,  the  area  of  whose  aperture  equalled  that  of  the  face  of  the  pi** 
was  placed  between  the  source  of  heat  and  the  body  under  trial,  while  a 
second  screen  served  to  intercept  all  radiation  until  the  moment  of  the  ex- 
periment. 

After  much  preliminary  labour  for  the  purpose  of  testing  the  capabilities 
of  the  apparatus  and  the  value  of  its  indications,  an  extended  series  of  re- 
searches was  undertaken  and  carried  on  during  a  long  period  with  great 
success  :  some  of  the  most  curious  results  are  given  in  the  subjoined  table. 

Four  different  sources  of  heat  were  employed  in  these  experiments,  dif- 
fering in  their  degrees  of  intensity :  the  naked  flame  of  an  oil-lamp ;  a  coiJ 


84 


TRANSMISSION    OF    HEAT. 


of  platinum  wire  heated  to  redness ;  blackened  copper  at  734°  (390°C) ;  and 
the  same  heated  to  212°  (100°C). 


Substances. 
(Thickness  of  plate  0-1  inch,  nearly.) 


Transmission  of  100  rays  of 
heat  from 


Ah 


Rock-salt,  transparent  and  colourless. 

Fluor-spar,  colourless 

Rock-salt,  muddy 

Beryl 

Fluor-spar,  greenish  

Iceland-spar 

Plate-glass 

Rock-crystal 

Rock-crystal,  brown 

Tourmaline,  dark  green 

Citric  acid,  transparent 

Alum,  transparent 

Sugar-candy 

Fluor-spar,  green,  translucent 

Ice,  pure  and  transparent 


92 

78 

65 

54 

46 

39 

39 

38 

37 

18 

11 

9 

8 

8 

6 


92 

69 

65 

23 

38 

28 

24 

28 

28 

16 

2 

2 

0 

6 

0 


92 

42 

65 

13 

24 

6 

6 

6 

6 

3 

0 

0 

0 

4 

0 


92 

33 

65 

0 

20 

0 

0 

0 

0 

0 

0 

0 

0 

3 

0 


On  examining  this  remarkable  table,  which  is  an  abstract  of  one  much 
more  extensive,  the  first  thing  that  strikes  the  eye  is  the  want  of  connection 
between  the  power  of  transmitting  heat  and  that  of  transmitting  light ; 
taking,  for  instance,  the  oil-lamp  as  the  source  of  heat,  out  of  a  quantity  of 
heat  represented  by  100  rays  falling  upon  the  pUe,  the  proportion  intercepted 
by  similar  plates  of  rock-salt,  glass,  and  alum,  may  be  expressed  by  the 
numbers,  8,  61,  and  91 ;  and  yet  these  bodies  are  equally  transparent  with 
respect  to  light.  Generally  speaking,  colour  was  found  to  interfere  with  the 
transmissive  power,  but  to  a  very  unequal  extent ;  thus,  in  fluor-spar,  colour- 
Jess,  greenish,  and  deep-green,  the  quantities  transmitted  were  78,  46,  and 
8,  while  the  diflFerence  between  colourless  and  brown  rock-crystal  was  only  1. 
Bodies  absolutely  opaque,  as  wood,  metals,  and  black  marble,  stopped  the 
rays  completely,  although  it  was  found  that  the  faculty  of  transmission  was 
possessed  to  a  certain  extent  by  some  which  were  nearly  in  that  condition, 
as  thick  plates  of  brown  quartz,  black  mica,  and  black  glass. 

When  rays  of  heat  had  once  passed  through  a  plate  of  any  substance,  the 
interposition  of  a  second  similar  plate  occasioned  much  less  loss  than  the 
first ;  the  same  thing  happened  when  a  number  were  interposed ;  the  rays, 
after  traversing  one  plate,  being  but  little  interrupted  by  others  of  a  similar 
nature. 

The  next  point  to  be  noticed  is  the  great  diflFerence  in  the  properties  of 
'■.he  rays  from  different  sources.  Out  of  100  rays  from  each  source  which 
fell  on  rock-salt,  the  same  proportion  was  always  transmitted,  whether  the 
rays  proceeded  from  the  intensely  heated  flame,  the  red-hot  platinum  wire, 
or  the  copper  at  734°  (390°C)  or  212°  (100°C);  but  this  is  true  of  no  other 
substance  in  the  list.  In  the  case  of  plate-glass,  we  have  the  numbers  39, 
24,  6,  and  0,  as  representatives  of  the  comparative  quantities  of  heat  trana 


TRANSMISSION    or    HEAT.  85 

mitted  through  the  plate  from  each  source ;  or  in  the  three  varieties  of  fluor- 
spar, as  below  stated : — 

Flame.  Eed-heat.      784°  (3900C).    212°  (lOOOC). 

Colourless  78  69  42  33 

Greenish 46  38  24  20 

Dark  green 8  6  4  3 

While  one  substance,  beryl,  out  of  100  rays  from  an  intensely  heated 
source,  sufiFers  54  to  pass,  and  from  the  same  number  (that  is,  an  equal 
quantity  of  heat)  from  metal  at  212°  (100°C),  none  at  all;  another,  fluor- 
spar, transmits  rays  from  the  two  sources  mentioned,  in  the  proportion  of 
8  to  3. 

These,  and  many  other  curious  phenomena,  are  fully  and  completely 
explained  on  the  supposition,  that  among  the  invisible  rays  of  heat  differ- 
ences are  to  be  found  exactly  analogous  to  those  difi'erences  between  the 
rays  of  light  which  we  are  accustomed  to  call  colours.  Rock-salt  and  air  are 
the  only  substances  yet  known  which  are  truly  diathermanous,  or  equally 
transparent  to  all  kinds  of  heat-rays  ;  they  are  to  the  latter  what  white  glass 
or  water  is  to  light ;  they  suffer  rays  of  every  description  to  pass  with  equal 
facility.  All  other  bodies  act  like  coloured  glasses,  absorbing  certain  of  the 
rays  more  abundantly  than  the  rest,  and  colouring,  as  it  were,  the  heat  which 
passes  through  them. 

These  heat-tints  have  no  direct  relation  to  ordinary  colours ;  their  exist- 
ence is,  nevertheless,  almost  as  clearly  made  out  as  that  of  the  coloured 
rays  of  the  spectrum.  Bodies  at  a  comparatively  low  temperature  emit  rays 
of  such  a  tint  only  as  to  be  transmissible  by  a  few  substances ;  as  the  tem- 
perature rises,  rays  of  other  heat-colours  begin  to  make  their  appearance, 
and  transmission  of  some  portion  of  these  rays  takes  place  through  a  greater 
number  of  bodies ;  while  at  the  temperature  of  intense  ignition  we  find  raya 
of  all  colours  thrown  out,  some  or  other  of  which  wiU  certainly  find  their 
way  through  a  great  variety  of  substances. 

By  cutting  rock-salt  into  prisms  and  lenses,  it  is  easy  to  show  that  radiant 
heat  may  be  reflected  like  ordinary  light,  and  its  beams  made  to  converge 
or  diverge  at  pleasure ;  and,  lastly,  to  complete  the  analogy,  it  has  been 
shown  to  be  susceptible  of  polarization  by  transmission  through  plates  of 
doubly-refracting  minerals,  in  the  same  manner  as  light  itself.' 

*  Dr.  Forbes,  Phil.  Mag.  for  1835;  also  M.  Melloni,  Ann.  Chem.  et  Phys.  Ixv.  5. 


'86  MAGNETISM. 


MAGNETISM. 

A  PARTICULAR  species  of  iron  ore  has  long  been  remarkable  for  its  pro- 
perty of  attracting  small  pieces  of  iron,  and  causing  them  to  adhere  to  its 
surface :  it  is  called  loadstone,  or  magnetic  iron  ore. 

If  a  piece  of  this  loadstone  be  carefully  examined,  it  will  be  found  that 
the  attractive  force  for  particles  of  iron  is  greatest  at  certain  particular 
points  of  its  surface,  while  elsewhere  it  is  much  diminished,  or  even  alto- 
gether absent.  These  attractive  points,  or  centres  of  greatest  force,  are 
denominated  poles,  and  the  loadstone  itself  is  said  to  be  endued  with  mag- 
netic polarity. 

If  one  of  the  poles  of  a  natural  loadstone  be  rubbed  in  a  particular  man- 
ner over  a  bar  of  steel,  its  characteristic  properties  will  be  communicated 
to  the  bar,  which  will  then  be  found  to  attract  iron-filings  like  the  loadstone 
itself.  Farther,  the  attractive  force  will  be  greatest  at  two  points  situated 
very  near  the  extremities  of  the  bar,  and  least  of  all  towards  the  middle. 
The  bar  of  steel  so  treated  is  said  to  be  magnetised,  or  to  constitute  an  arti- 
ficial magnet. 

When  a  magnetised  bar  or  natural  magnet  is  suspended  at  its  centre  in 
any  convenient  manner,  so  as  to  be  free  to  move  in  a  horizontal  plane,  it  is 
always  found  to  assume  a  particular  direction  with  regard  to  the  earth,  one 
end  pointing  nearly  north  and  the  other  nearly  south.  If  the  bar  be  moved 
from  this  position,  it  will  tend  to  re-assume  it,  and,  after  a  few  oscillations, 
settle  at  rest  as  before.  The  pole  which  points  towards  the  astronomical 
north  is  usually  distinguished  as  the  north  pole  of  the  bar,  and  that  which 
points  southward,  as  the  south  pole.  A  suspended  magnet,  either  natural 
or  artificial,  of  symmetrical  form,  serves  to  exhibit  certain  phenomena  of 
attraction  and  repulsion  in  the  presence  of  a  second  magnet,  which  deserve 
particular  attention.  When  a  north  pole  is  presented  to  a  south  pole,  or  a 
south  pole  to  a  north,  attraction  ensues  between  them ;  the  ends  of  the  bars 
approach  each  other,  and,  if  permitted,  adhere  with  considerable  force ; 
when,  on  the  other  hand,  a  north  pole  is  brought  near  a  second  north  pole, 
or  a  south  pole  near  another  south  pole,  mutual  repulsion  is  observed,  and 
the  ends  of  the  bars  recede  from  each  other  as  far  as  possible.  Poles  of  an 
opposite  name  attract,  and  of  a  similar  name  repel  each  other.  Thus,  a  small 
bar  or  needle  of  steel,  properly  magnetized  and  suspended,  and  having  its 
poles  marked,  becomes  an  instrument  fitted  not  only  to  discover  the  exist- 
ence of  magnetic  power  in  other  bodies,  but  to  estimate  the  kind  of  polarity 
affected  by  their  different  parts. 

A  piece  of  iron  brought  into  the  neighbourhood  of  a  magnet  acquires  itself 
magnetic  properties ;  the  intensity  of  the  power  thus  conferred  depends 
upon  that  of  the  magnet  and  upon  the  interval  which  divides  the  two ;  be- 
coming greater  as  that  interval  decreases,  and  greatest  of  all  when  in  actual 
contact.  The  iron  under  these  circumstances  is  said  to  be  magnetized  by 
induction  or  influence,  and  the  effect,  which  in  an  instant  reaches  its  maxi- 
mum, is  at  once  destroyed  by  removing  the  magnet. 

When  steel  is  substituted  for  iron  in  this  experiment,  the  inductive  action 
is  hardly  perceptible  at  first,  and  only  becomes  manifest  after  the  lapse  of  a 
certain  time ;  in  this  condition,  when  the.  steel  bar  is  removed  from  the  mag- 


MAGNETISM 


87 


Fig.  60. 


net,  it  retains  a  portion  of  the  induced  polarity.  It  becomes,  indeed,  a  per- 
manent magnet,  similar  to  the  first,  and  retains  its  peculiar  properties  for 
an  indefinite  period. 

A  particular  name  is  given  to  this  resistance  which  steel  always  ofi'ers  in 
a  greater  or  less  degree  both  to  the  development  of  magnetism  and  its  sub- 
sequent destruction;  it  is  called  specific  coercive  power. 

The  rule  which  regulates  the  induction  of  magnetic  polarity  in  all  cases 
is  exceedingly  simple,  and  most  important  to  be  remembered.  The  pole  pro- 
duced is  always  of  the  opposite  name 
to  that  which  produced  it,  a  north  pole 
developing  south  polarity,  and  a  south 
pole  north  polarity.  The  north  pole  of 
the  magnet,  shown  in  fig.  60,  induces 
south  polarity  in  all  the  nearer  extre- 
mities of  the  pieces  of  iron  or  steel 
which  surround  it,  and  a  state  similar 
to  its  own  in  all  the  more  remote  extre- 
mities. The  iron  thus  magnetized  is 
capable  of  exerting  a  similar  inductive 
action  on  a  second  piece,  and  that  upon 
a  third,  and  so  to  a  great  number,  the 
intensity  of  the  force  diminishing  aa 
the  distance  from  the  permanent  mag- 
net increases.  It  is  in  this  way  that  a 
magnet  is  enabled  to  hold  up  a  number 
of  small  pieces  of  iron,  or  a  bunch  of 
filings,  each  separate  piece  becoming  a 
magnet  for  the  time  by  induction. 

Magnetic  polarity,  similar  to  that  which  iron  presents,  has  been  found 
only  in  some  of  the  compounds  of  iron,  in  nickel,  and  in  cobalt. 

Magnetic  attractions  and  repulsions  are  not  in  the  slightest  degree  inter- 
fered with  by  the  interposition  of  substances  destitute  of  magnetic  proper- 
ties. Thick  plates  of  glass,  shellac,  metals,  wood,  or  of  any  substances 
except  those  above  mentioned,  may  be  placed  between  a  magnet  and  a  sus- 
pended needle,  or  a  piece  of  iron  under  its  influence,  the  distance  being  pre- 
served, without  the  least  perceptible  alteration  in  its  attractive  power,  or 
force  of  induction. 

One  kind  of  polarity  cannot  be  exhibited  without  the  other.  In  other 
words,  a  magnetic  pole  cannot  be  insulated.  If  a  magnetized  bar  of  steel 
be  broken  at  its  neutral  point,  or  in  the  middle,  each  of  the  broken  ends  ac- 
quires an  opposite  pole,  so  that  both  portions  of  the  bar  become  perfect 
magnets ;  and,  if  the  division  be  carried  still  farther,  if  the  bar  be  broken 
into  a  hundred  pieces,  each  fragment  will  be  a  complete  magnet,  having  its 
own  north  and  south  poles. 

This  experiment  serves  to  show  very  clearly  that  the  apparent  polarity  of 
the  bar  is  the  consequence  of  the  polarity  of  each  individual  particle,  the 
poles  of  the  bar  being  merely  points  through  which  the  resultants  of  all 
these  forces  pass ;  the  large  magnet  is  made  up  of  an  immense  number  of 
little  magnets  regularly  arranged  side  by  side  (fig.  61),  all  having  their  north 

Fig.  61.  / 


8B  MAGNETISM. 

poles  looking  one  way,  and  their  south  poles  the  other.  The  middle  portion 
of  such  a  system  cannot  possibly  exhibit  attractive  or  repulsive  effects  on  an 
external  body,  because  each  pole  is  in  close  juxta-position  with  one  of  an 
opposite  name  and  of  equal  power ;  hence  their  forces  will  be  exerted  in  op- 
posite directions  and  neutralize  each  other's  influence.  Such  will  not  be  the 
case  at  the  extremities  of  the  bar ;  there  uncompensated  polarity  will  be 
found  capable  of  exerting  its  specific  power. 

This  idea  of  regular  polarization  of  particles  of  matter  in  virtue  of  a  pair 
of  opposite  and  equal  forces,  is  not  confined  to  magnetic  phenomena ;  it  is 
the  leading  principle  in  electrical  science,  and  is  constantly  reproduced  in 
some  form  or  other  in  every  discussion  involving  the  consideration  of  mole- 
cular forces. 

Artificial  steel  magnets  are  made  in  a  great  variety  of  forms;  such  as 
small  light  needles,  mounted  with  an  agate  cap  for  suspension  upon  a  fine 
point ;  straight  bars  of  various  kinds ;  bars  curved  into  the  shape  of  a  horse- 
shoe, &c.  All  these  have  regular  polarity  communicated  to  them  by  cer- 
tain processes  of  rubbing  or  touching  with  another  magnet,  which  require 
care,  but  are  not  otherwise  dijB&cult  of  execution.  When  great  power  is 
wished  for,  a  number  of  bars  may  be  screwed  together,  with  their  similar 
ends  in  contact,  and  in  this  way  it  is  easy  to  construct  permanent  steel  mag- 
nets capable  of  sustaining  great  weights.  To  prevent  the  gradual  destruc- 
tion of  magnetic  force,  which  would  otherwise  occur,  it  is  usual  to  arm  eacli 
pole  with  a  piece  of  soft  iron  or  keeper,  which,  becoming  magnetized  by  in- 
duction, serves  to  sustain  the  polarity  of  the  bar,  and  even  increases  in  som^ 
cases  its  energy. 

The  direction  spontaneously  assumed  by  a  suspended  needle  indicates  that 
the  earth  itself  has  the  properties  of  an  enormous  magnet,  whose  south  pole 
is  in  the  northern  hemisphere.  A  line  joining  the  two  poles  of  such  a 
needle  or  bar  indicates  the  direction  of  the  magnetic  meridian  of  the  place, 
which  is  a  vertical  plane  coincident  with  the  direction  of  the  needle. 

The  magnetic  meridian  of  a  place  is  not  usually  coincident  with  its  geo- 
graphical meridian,  but  makes  with  the  latter  a  certain  angle  called  the  de- 
clination of  the  needle;  in  other  words,  the  magnetic  poles  are  not  situated 
within  the  line  of  the  axis  of  rotation. 

The  amount  of  this  declination  of  the  needle  from  the  true  north  and 
south  not  only  varies  at  different  places,  but  in  the  same  place  is  subject  to 
daily,  yearly,  and  secular  fluctuations,  which  are  called  the  variations  of 
declination.  Thus>  at  the  commencement  of  the  17th  century,  the  declina- 
tion was  eastward ;  in  1660,  it  was  0 ;  that  is,  the  needle  pointed  due  north 
and  south.  Afterwards  it  became  westerly,  slowly  increasing  until  the  year 
1818,  when  it  reached  24°  30'',  since  which  time  it  has  been  slowly  di- 
minishing. 

If  a  steel  bar  be  supported  on  a  horizontal  axis  passing  exactly  through 
its  centre  of  gravity,  it  will  of  course  remain  equally  balanced  in  any  posi- 
tion in  which  it  may  happen  to  be  placed ;  if  the  bar  so  adjusted  be  then 
magnetized,  it  will  be  found  to  take  a  permanent  direction,  the  north  pole 
being  downwards,  and  the  bar  making  an  angle  of  about  70°,  with  a  hori- 
zontal plane  passing  through  the  axis.  This  is  called  the  dip,  or  inclination 
of  the  needle,  and  shows  the  direction  in  which  the  force  of  terrestrial  mag- 
netism is  most  energetically  exerted.  The  amount  of  this  dip  is  different  in 
different  latitudes ;  near  the  equator  it  is  very  small,  the  needle  remaining 
nearly  or  quite  horizontal ;  as  the  latitude  increases  the  dip  becomes  more 
decided ;  and  over  the  magnetic  pole  the  bar  becomes  completely  vertical. 
Such  a  situation  is  in  fact  to  be  found  in  the  northern  hemisphere,  consider- 
ably to  the  westward  of  the  geographical  pole,  in  Prince  Regent's  Inlet. 
lat.  70^  5^  N.  and  longitude  96°  W  W. ;  the  dipping-needle  has  here  been 


MAGNETISM.  89 

seen  to  point  directly  downwards,  while  the  horizontal  or  compass-needle 
ceased  to  traverse.  The  position  of  the  south  magnetic  pole  has  lately  been 
determined,  by  the  observations  of  Captain  Ross,  to  be  about  lat.  73°  S.  and 
long.  130°  E. 

By  observing  a  great  number  of  points  near  the  equator  in  which  the  dip 
becomes  reduced  to  nothing,  a  line  may  be  traced  around  the  earth,  called 
the  magnetic  equator,  and  nearly  parallel  to  this,  on  both  sides,  a  number 
of  smaller  circles,  called  lines  of  equal  dip.  These  lines  present  great  irreg- 
ularities when  compared  with  the  equator  itself  and  the  parallels  of  lati- 
tude, the  magnetic  equator  deviating  from  the  terrestrial  one  as  much  as  12° 
at  its  point  of  greatest  divergence.  Like  the  horizontal  declination,  the  dip 
ia  also  subject  to  change  at  the  same  place.  Observations  have  not  yet  been 
made  during  sufficient  time  to  determine  accurately  the  law  and  rate  of  alte- 
ration, and  great  practical  difficulties  exist  also  in  the  construction  of  the 
instruments.  In  the  year  1773  it  was  about  72° ;  at  the  present  time  it  is 
near  69°  5^  in  London. 

The  inductive  power  of  the  magnetism  of  the  earth  may  be  shown  by 
holding  in  a  vertical  position  a  bar  of  very  soft  iron ;  the  lower  end  will  be 
found  to  possess  north  polarity,  and  the  upper,  the  contrary  state.  On  re- 
versing the  bar  the  poles  are  also  reversed.  AH  masses  of  iron  whatever, 
when  examined  by  a  suspended  needle,  will  be  found  in  a  state  of  magnetic 
polarity  by  the  influence  of  the  earth ;  iron  columns,  tools  in  a  smith's  shop, 
fire-irons,  and  other  like  objects,  are  all  usually  magnetic,  and  those  made 
of  steel  permanently  so.  On  board  ship,  the  presence  of  so  many  large 
masses  of  iron,  guns,  anchors,  water-tanks,  &c.,  thus  polarized  by  the  earth, 
causes  a  derangement  of  the  compass-needles  to  a  very  dangerous  extent ; 
happily,  a  plan  has  been  devised  for  determining  the  amount  of  this  local 
attraction  in  different  positions  of  the  ship,  and  making  suitable  corrections. 

The  mariner's  compass,  which  is  nothing  more  than  a  suspended  needle 
attached  to  a  circular  card  marked  with  the  points,  was  not  in  general  use 
in  Europe  before  the  year  1300,  although  the  Chinese  have  had  it  from  very 
early  antiquity.  Its  value  to  the  navigator  is  now  very  much  increased  by 
correct  observations  of  the  exact  amount  of  the  declination  in  various  parts 
of  the  world. 

Probably  every  substance  in  the  world  contributes  something  to  the  mag- 
netic action  of  the  earth ;  for,  according  to  the  latest  discoveries  of  Mr. 
Faraday,  magnetism  is  not  peculiar  to  those  substances  which  have  more 
especially  been  called  magnetic,  such  as  iron,  nickel,  cobalt,  but  it  is  the 
property  of  all  matter,  though  to  a  much  smaller  degree.  Very  powerful 
magnets  are  required  to  show  this  remarkable  fact.  Large  horse-shoe  mag- 
nets, made  by  the  action  of  the  electric  current,  are  most  proper.  The 
magnetic  action  on  different  substances  which  are  capable  of  being  easily 
moved,  differs  not  only  according  to  the  size,  but  also  according  to  the  nature 
of  the  substance.  In  consequence  of  this,  Faraday  divides  all  bodies  into 
two  classes.  He  calls  the  one  magnetic,  or,  better,  paramagnetic,  and  the 
other  diamagnetic. 

The  matter  of  which  a  paramagnetic  (magnetic)  body  consists  is  attracted 
by  both  poles  of  the  horse-shoe  magnet ;  on  the  contrary,  the  matter  of  a 
diamagnetic  body  is  repelled.  When  a  small  iron  bar  is  hung  by  untwisted 
Bilk  between  the  poles  of  the  magnet,  so  that  its  long  diameter  can  easily 
move  in  a  horizontal  plane,  it  arranges  itself  axially,  that  is,  parallel  to  the 
straight  line  which  joins  the  poles,  or  to  the  magnetic  axis  of  the  poles; 
assuming  at  the  end  which  is  nearest  the  north  pole,  a  south  pole,  and  at 
the  end  nearest  the  south  pole,  a  north  pole.  Whenever  the  little  bar  is 
dremoved  from  this  position,  after  a  few  oscillations,  it  returns  again  to  its 
previous  position.  The  whole  class  of  paramagnetic  bodies  behave  in  a  nre- 
8* 


90  MAGNETISM. 

cisely  similar  way  under  similar  circumstances ;  only  in  the  intensity  of  the 
effects  great  diflferences  occur. 

On  the  contrary,  diamagnetic  bodies  have  their  long  diameters  placed 
equatorially,  that  is,  at  right  angles  to  the  magnetic  axis.  They  behave,  as 
if  at  the  end  opposite  to  each  pole  of  the  magnet,  the  same  kind  of  polarity 
existed. 

In  the  first  class  of  substances,  besides  iron,  which  is  the  best  representa- 
tive of  the  class,  we  have  nickel,  cobalt,  manganese,  chromium,  cerium, 
titanium,  palladium,  platinum,  osmium,  aluminium,  oxygen,  and  also  most 
of  the  compoimds  of  these  bodies ;  most  of  them,  even  when  in  solution. 
According  to  Faraday,  the  following  substances  are  also  feebly  paramagnetic 
(magnetic) ;  paper,  sealing-wax,  indian-ink,  porcelain,  asbestos,  fluor-spar, 
minium,  cinnabar,  binoxide  of  lead,  sulphate  of  zinc,  tourmaline,  graphite, 
and  charcoal. 

In  the  second  class  are  placed  bismuth,  antimony,  zinc,  tin,  cadmium, 
sodium,  mercury,  lead,  silver,  copper,  gold,  arsenic,  uranium,  rhodium, 
iridium,  tungsten,  phosphorus,  iodine,  sulphur,  chlorine,  hydrogen,  and  many 
of  their  compounds.  Also,  glass  free  from  iron,  water,  alcohol,  ether,  nitric 
acid,  hydrochloric  acid,  resin,  wax,  olive  oil,  oil  of  turpentine,  caoutchouc, 
sugar,  starch,  gum,  and  wood.     These  are  diamagnetic. 

If  diamagnetic  and  paramagnetic  bodies  are  combined,  their  peculiar  pro- 
perties are  destroyed.  In  most  of  these  compounds,  occasionally,  in  conse- 
quence of  the  presence  of  the  smallest  quantity  of  iron,  the  peculiar  mag- 
netic power  remains  more  or  less  in  excess.  Thus  green  bottle  glass  and  many 
varieties  of  crown  glass  are  magnetic  in  consequence  of  the  iron  in  them. 

In  order  to  examine  the  magnetic  properties  of  fluids  they  are  placed  in 
very  thin  glass  tubes,  the  ends  of  which  are  closed  by  melting,  they 
are  then  hung  horizontally  between  the  poles  of  the  magnet.  Under  the 
influence  of  poles  sufficiently  powerful,  they  begin  to  swing,  and  accord- 
ing as  the  fluid  contents  are  paramagnetic  (magnetic),  or  diamagnetic,  they 
assume  an  axial  or  equatorial  position. 

Under  certain  circumstances  substances  which  belong  to  the  paramagnetic 
class  behave  as  if  they  were  diamagnetic.  This  happens  in  consequence  of 
a  diff"erential  action.  Thus,  for  example,  when  a  glass  tube  full  of  a  dilute 
solution  of  sulphate  of  iron  is  allowed  to  swing  in  a  concentrated  solution 
of  sulphate  of  iron,  instead  of  in  the  air,  it  assumes  an  equatorial  position. 
The  air,  in  consequence  of  the  oxygen  in  it,  is  itself  paramagnetic  (magnetic). 
Hence  such  bodies  as  appear  to  possess  feeble  diamagnetic  properties,  can 
only  show  their  true  properties  when  hung  in  a  vacuum. 

Faraday  has  tried  the  magnetic  condition  of  gases  in  difi*erent  ways.  One 
way  consisted  in  making  soap  bubbles  with  the  gas  which  he  wished  to  in- 
vestigate, and  bringing  these  near  the  poles.  Soap  and  water  alone  is  feebly 
diamagnetic.  A  bubble  filled  with  oxygen  was  strongly  attracted  by  the 
magnet.  All  other  gases  in  the  air  are  diamagnetic,  that  is,  they  are  re- 
pelled. But,  as  Faraday  has  shown,  in  a  difi'erent  way,  this  partly  arises 
from  the  paramagnetic  (magnetic)  property  of  the  air.  Thus  he  found  that 
nitrogen,  when  this  difi"erential  action  was  eliminated,  was  perfectly  indif- 
ferent, whether  it  was  condensed  or  rarified,  whether  cooled  or  heated. 
When  the  temperature  is  raised,  the  diamagnetic  property  of  gases  in  the 
air  is  increased.  Hence  the  flame  of  a  candle  or  of  hydrogen  is  strongly 
repelled  by  the  magnet.     Even  warm  air  is  diamagnetic  in  cold  air. 

For  some  time  it  has  been  believed  that  bodies  in  a  crystalline  form  had  a 
special  and  peculiar  behaviour  when  placed  between  the  poles  of  a  magnet. 
It  appeared  as  though  the  magnetic  directing  power  of  the  crystal  had  some 
peculiar  relation  to  the  position  of  its  optic  axis ;  so  that,  independently  of  « 
the  magnetic  pi*operty  of  the  substance  of  the  crystal,  if  the  crystal  was 


MAGNETISM.  91 

positively  optical,  it  possessed  the  power  of  placing  Its  optic  axis  parallel 
with  the  line  which  joined  the  poles  of  the  magnet,  while  optically  negative 
crystals  tried  to  arrange  their  axes  at  right  angles  to  this  line.  This  suppo- 
sition is  disproved  by  the  excellent  investigation  of  Knoblauch  and  Tyndall. 
It  follows  from  their  observations  that  the  peculiarity  in  regard  to  crystals 
is  dependent  on  their  internal  state  of  cohesion,  that  is,  on  unequal  com- 
pression in  different  directions.  If  crystalline,  or  even  uncrystalline  sub- 
stances are  unequally  compressed  in  diflFerent  directions,  they  are  found  to 
possess  a  preponderating  directive  force  in  the  direction  in  which  they  are 
most  strongly  compressed,  so  that  when  this  direction  does  not  coincide  with 
the  long  diameter  of  the  body,  magnetic  bodies  will  even  arrange  themselvei 
equatorially,  and  diamagnetic  bodies  axially. 


1» 


^2  ELECTEICITY. 


ELECTRICITY. 

If  glass,  amber,  or  sealing-wax,  be  rubbed  with  a  dry  cloth,  it  acquires  the 
power  of  attracting  light  bodies,  as  feathers,  dust,  or  bits  of  paper ;  this  is 
tne  result  of  a  new  and  peculiar  condition  of  the  body  rubbed,  called  elec- 
trical excitation. 

If  a  liglit  downy  feather  be  suspended  by  a  thread  of  white  silk,  and  a 
dry  glass  tube,  excited  by  rubbing,  be  presented  to  it,  the  feather  will  be 
strongly  attracted  to  the  tube,  adhere  to  its  surface  for  a  few  seconds,  and 
then  fall  oflF.  If  the  tube  be  now  excited  anew,  and  presented  to  the  feather, 
the  latter  will  be  strongly  repelled. 

The  same  experiment  may  be  repeated  with  shellac  or  resin ;  the  feather 
in  its  ordinary  state  will  be  drawn  towards  the  excited  body,  and  after 
touching,  again  driven  from  it  with  a  certain  degree  of  force. 

Now,  let  the  feather  be  brought  into  contact  with  the  excited  glass,  so  as 
to  be  repelled  by  that  substance,  and  let  a  piece  of  excited  sealing-wax  be 
presented  to  it ;  a  degree  of  attraction  will  be  observed  far  exceeding  that 
exhibited  when  the  feather  is  in  its  ordinary  state.  Or,  again,  let  the  feather 
be  made  repulsive  for  sealing-wax,  and  then  the  excited  glass  be  presented ; 
strong  attraction  will  ensue. 

The  reader  will  at  once  see  the  perfect  parallelism  between  the  effects 
described  and  some  of  the  phenomena  of  magnetism ;  the  electrical  excite- 
ment having  a  twofold  nature,  like  the  opposite  polarities  of  the  magnet. 
A  body  to  which  one  kind  of  excitement  has  been  communicated  is  attracted 
by  another  body  in  the  opposite  state,  and  repelled  by  one  in  the  same  state. 
The  excited  glass  and  resin  being  to  each  other  as  the  north  and  south  poles 
of  a  pair  of  magnetized  bars. 

To  distinguish  these  two  different  forms  of  excitement,  terms  are  em- 
ployed, which,  although  originating  in  some  measure  in  theoretical  views  of 
the  nature  of  the  electrical  disturbance,  may  be  understood  by  the  student 
as  purely  arbitrary  and  distinctive ;  it  is  customary  to  call  the  electricity 
manifested  by  glass  positive  or  vitreous,  and  that  developed  in  the  case  of 
shellac,  and  bodies  of  the  same  class,  negative  or  resinous.  The  kind  of  elec- 
tricity depends  in  some  measure  upon  the  nature  of  the  surface ;  smooth 
glass  rubbed  with  silk  or  wool  becomes  ordinarily  positive,  but  when  ground 
or  roughened  by  sand  or  emery,  it  acquires,  under  the  same  circumstances, 
a  negative  charge. 

The  repulsion  shown  by  bodies  in  the  same  electricat  state  is  taken  advan- 
tage of  to  construct  instruments  for  indicating  electrical  excitement  and 
pointing  out  its  kind.  Two  balls  of  alder-pith  (fig.  62),  hung  by  threads  or 
very  fine  metal  wires,  serve  this  purpose  in  many  cases ;  they  open  out  when 
excited,  in  virtue  of  their  mutual  repulsion,  and  show  by  the  degree  of  diver- 
gence the  extent  to  which  the  excitement  has  been  carried.  A  pair  of  gold 
leaves  suspended  beneath  a  bell  jar,  and  communicating  with  a  metal  cap 
above  (fig.  63),  constitute  a  much  more  delicate  arrangement,  and  one  of 
great  value  in  all  electrical  investigations.  These  instruments  are  called 
electroscopes  or  electrometers ;  when  excited  by  the  communication  of  a 
known  kind  of  electricity,  they  show,  by  an  increased  or  diminished  diver- 
gence, the  state  of  an  electrified  body  brought  into  their  neighbourhood. 


ELECTRICITY.  93 

Fig.  62.  Fig.  63. 


•<  >^ 


One  kind  of  electricity  can  no  more  be  developed  •without  the  other  than 
one  kind  of  magnetism ;  the  rubber  and  the  body  rubbed  always  assume 
opposite  states,  and  the  positive  condition  on  the  surface  of  a  mass  of  matter 
is  invariably  accompanied  by  a  negative  state  in  all  surrounding  bodies. 

The  induction  of  magnetism  in  soft  iron  has  its  exact  counterpart  in  elec- 
tricity ;  a  body  already  electrified  disturbs  or  polarizes  the  particles  of  all 
surrounding  substances  in  the  same  manner  and  according  to  the  same  law, 
inducing  a  state  opposite  to  its  own  in  the  nearer  portions,  and  a  similar 
state  in  the  more  remote  parts.  A  series  of  globes  suspended  by  silk  threads, 
in  the  manner  represented  in  fig.  64,  will  each  become  electric  by  induction 

Fig.  64. 


^   -Q+  Q*  -Q' 


when  a  charged  body  is  brought  near  the  end  of  the  series,  like  so  many 
pieces  of  iron  in  the  vicinity  of  a  magnet,  the  positive  half  of  each  globe 
looking  in  one  and  the  same  direction,  and  the  negative  half  in  the  opposite 
one.     The  positive  and  negative  signs  are  intended  to  represent  the  states. 

The  intensity  of  the  induced  electrical  disturbance  diminishes  with  the 
distance  from  the  charged  body ;  if  this  be  removed  or  discharged,  all  the 
effects  cease  at  once. 

So  far,  the  greatest  resemblance  may  be  traced  between  these  two  sets  of 
phenomena ;  but  here  it  seems  in  great  measure  to  cease.  The  magnetic 
polarity  of  a  piece  of  steel  can  awaken  polarity  in  a  second  piece  in  contact 
with  it  by  the  act  of  induction,  and  in  so  doing  loses  nothing  whatever  of 
its  power ;  this  is  an  eflFect  completely  different  from  the  apparent  transfer 
or  discharge  of  electricity  constantly  witnessed,  which  in  the  air  and  in 
liquids  often  give  rise  to  the  appearance  of  a  bright  spark  of  fire.  Indeed, 
ordinary  magnetic  effects  comprise  two  groups  of  phenomena  only,  those 
namely  of  attraction  and  repulsion,  and  those  of  induction.  But  in  elec- 
tricity, in  addition  to  phenomena  very  closely  resembling  these,  we  have  the 
effects  of  discharge,  to  which  there  is  nothing  analogous  in  magnetism,  and 
which  takes  place  in  an  instant  when  any  electrified  body  is  put  in  commu 


94  ELECTRICITY. 

nicatioa  with  the  earth  by  any  one  of  the  class  of  substances  called  con- 
ductors of  electricity ;  all  signs  of  electrical  disturbance  then  ceasing. 

These  conductors  of  electricity,  which  thus  permit  discharge  to  take  place- 
through  their  mass,  are  contrasted  with  another  class  of  substances  called 
non-conductors  or  insulators.  The  difference,  however,  is  only  one  of  degree, 
not  of  kind ;  the  very  best  conductors  offer  a  certain  resistance  to  the  elec- 
trical discharge,  and  the  most  perfect  insulators  permit  it  to  a  small  extent. 
The  metals  are  by  far  the  best  conductors ;  glass,  silk,  shellac,  and  dry  gas, 
or  vapour  of  any  sort,  the  very  worst ;  and  between  these  there  are  bodies 
of  all  degrees  of  conducting  power. 

Electrical  discharges  take  place  silently  and  without  disturbance  in  good 
conductors  of  sufficient  size.  But  if  the  charge  be  very  intense,  and  the 
conductor  Tery  small  or  imperfect  from  its  nature,  it  is  often  destroyed  with 
violence.       *■ 

When  a  break  is  made  in  a  conductor  employed  in  effecting  the  discharge 
of  a  highly-excited  body,  disruptive  or  spark-discharge,  so  well  known,  takes 
place  across  the  intervening  air,  provided  the  ends  of  the  conductor  be  not 
too  distant.  The  electrical  spark  itself  presents  many  points  of  interest  in 
the  modifications  to  which  it  is  liable. 

The  time  of  transit  of  the  electrical  wave  through  a  chain  of  good  conduct- 
ing bodies  of  great  length  is  so  minute  as  to  be  altogether  inappreciable  to 
ordinary  means  of  observation.  Professor  Wheatstone's  very  ingenious  ex- 
periments on  the  subject  give,  in  the  instance  of  motion  through  a  copper 
wire,  a  velocity  approaching  that  of  light. 

Electrical  excitation  is  apparent  only  upon  the  surfaces  of  bodies,  or  those 
portions  directed  towards  other  objects  capable  of  assuming  the  opposite 
state.  An  insulated  ball  charged  with  positive  electricity,  and  placed  in  the 
centre  of  the  room,  is  maintained  in  that  state  by  the  inductive  action  of  the 
walls  of  the  apartment,  which  immediately  become  negatively  electrified  ;  in 
the  interior  of  the  ball  there  is  absolutely  no  electricity  to  be  found,  although 
it  may  be  constructed  of  open  metal  gauze,  with  meshes  half  an  inch  wide. 
Even  on  the  surface  the  distribution  of  electrical  force  will  not  always  be  the 
same ;  it  will  depend  upon  the  figure  of  the  body  itself,  and  its  position  with 
regard  to  surrounding  objects.  The  polarity  will  always  be  highest  in  the 
projecting  extremities  of  the  same  conducting  mass,  and  greatest  of  all  when 
these  are  attenuated  to  points,  in  which  case  the  inequality  becomes  so  great 
that  discharge  takes  place  to  the  air,  and  the  excited  condition  cannot  be 
maintained. 

The  construction  and  use  of  the  common  electrical  machine,  and  other 
pieces  of  apparatus  of  great  practical  utility,  will,  by  the  aid  of  these  prin- 
ciples, become  intelligible. 

A  glass  cylinder  (fig.  65)  is  mounted  with  its  axis  in  a  horizontal  position, 
and  provided  with  a  handle  or  winch  by  which  it  may  be  turned.  A  leather 
cushion  is  made  to  press  by  a  spring  against  one  side  of  the  cylinder,  while 
a  large  metal  conducting  body,  armed  with  a  number  of  points  next  the 
glass,  occupies  the  other ;  both  cushion  and  conductor  are  insulated  by  glass 
supports,  and  to  the  upper  edge  of  the  former  a  piece  of  silk  is  attached 
long  enough  to  reach  half  round  the  cylinder.  Upon  the  cushion  is  spread 
a  quantity  of  a  soft  amalgam  of  tin,  zinc,  and  mercury,'  mixed  up  with  a 
little  grease ;  this  substance  is  found  by  experience  to  excite  glass  most 
powerfully.  The  cylinder,  as  it  turns,  thus  becomes  charged  by  friction 
against  the  rubber,  and  as  quickly  discharged  by  the  row  of  points  attached 
to  the  great  conductor ;  and  as  the  latter  is  also  completely  insulated,  its 
surface  speedily  acquires  a  charge  of  positive  electricity,  which  may  be 

1  Part  tin,  2  zinc,  and  6  mercury. 


ELECTRICITY. 

Tig.  65. 


93 


communicated  by  contact  to  other  insulated  bodies.  The  maximum  effect  is 
produced  when  the  rubber  is  connected  by  a  chain  or  wire  with  the  earth. 
If  negative  electricity  be  wanted,  the  rubber  must  be  insulated  and  the  con- 
ductor discharged. 

Another  form  of  the  electrical  machine  consists  of  a  circular  plate  of  glass 
(fig.  66)  moving  upon  an  axis,  and  provided  with  two  pairs  of  cushions  or 

Fig.  66. 


M  ELECTRICITY. 

or  rubbers,  attached  to  the  upper  and  lower  parts  of  the  wooden  frame, 
covered  with  amalgam,  between  which  the  plate  moves  with  considerable 
friction.  An  insulated  conductor,  armed  as  before  with  points,  discharges 
the  plate  as  it  turns,  the  nibbers  being  at  the  same  time  connected  with  the 
ground  by  the  wood-work  of  the  machine,  or  by  a  stiip  of  metal.  This 
modification  of  the  apparatus  is  preferred  in  all  cases  where  considerable 
power  is  wanted. 

In  the  practical  management  of  electrical  apparatus,  great  care  must  be 
taken  to  prevent  deposition  of  moisture  from  the  air  upon  the  surface  of  the 
glass  supports,  which  should  always  be  varnished  with  fine  lac  dissolved  in 
^alcohol ;  the  slightest  film  of  water  is  sufficient  to  destroy  the  power  of  insu- 
lation. The  rubbers  also  must  be  carefully  dried  before  use,  and  the  amal- 
gam renewed  if  needful ;  in  damp  weather  much  trouble  is  often  experienced 
in  bringing  the  machine  into  powerful  action. 

When  the  conductor  of  the  machine  is  charged  with  electricity,  it  acts 
indirectly  on,  and  accumulates  the  contrary  electricity  to  its  own,  at  the  sur- 
face of  all  the  surrounding  conductors.  It  produces  the  greatest  effect  on 
the  conductor  that  is  nearest  to  it,  and  which  is  in  the  best  connection  with 
the  ground,  whereby  the  electricity  of  the  same  kind  as  that  of  the  machine 
may  pass  to  the  earth.  As  the  inducing  electricity  attracts  the  induced 
electricity  of  an  opposite  kind ;  so,  on  the  other  hand,  is  the  former  attracted 
by  the  latter.  Hence  the  fluid  which  the  conductor  receives  from  the  ma- 
chine must  especially  accumulate  at  that  spot  to  which  another  good  con- 
ductor of  electricity  is  opposed.  If  a  metal  disc  is  in  connection  with  the 
conductor  of  a  machine,  and  if  another  similar  disc,  which  is  in  good  con- 
nection with  the  earth,  is  placed  opposite  to  it,  we  have  an  arrangement  by 
■which  tolerably  large  and  good  conducting  surfaces  can  be  brought  close  to 
one  another;  thus  the  positive  condition  of  the  first  disc,  as  well  as  the  nega- 
tive condition  of  the  other,  must  be  increased  to  a  very  considerable  degree ; 
the  limit  is  in  this  case,  however,  soon  reached,  because  the  intervening  air 
easily  permits  spark-discharge  to  take  place  through  its  substance.  With  a 
*  solid  insulating  body,  as  glass  or  lac,  this  happens  with 
Fig.  67.  much  greater  difficulty,  even  when  the  plate  of  insulating 

matter  is  very  thin.  It  is  on  this  principle  that  instru- 
ments for  the  accumulation  of  electricity  depend,  among 
which  the  Ley  den  jar  is  the  most  important. 

A  thin  glass  jar  (fig.  67)  is  coated  on  both  sides  with  tin- 
foil, care  being  taken  to  leave  several  inches  of  the  upper 
part  uncovered ;  a  wire,  terminating  in  a  metallic  knob, 
communicates  with  the  internal  coating ;  when  the  outside 
of  the  jar  is  connected  with  the  earth,  and  the  knob  put 
in  contact  with  the  conductor  of  the  machine,  the  inner 
and  outer  surfaces  of  the  glass  become  respectively  posi- 
tive and  negative,  until  a  very  great  degree  of  intensity 
has  been  attained.    On  completing  the  connection  between 
the  two  coatings  by  a  metallic  wire  or  rod,  discharge  oc- 
curs in  the  form  of  an  exceedingly  bright  spark,  accom- 
panied by  a  loud  snap ;  and  if  the  body  be  interposed  in  the  circuit,  the 
peculiar  and  disagreeable  sensation  of  the  electric  shock  is  felt  at  the  mo- 
ment of  its  completion. 

By  enlarging  the  dimensions  of  the  jar,  or  by  connecting  together  a  number 
in  such  a  manner  that  all  may  be  charged  and  discharged  simultaneously, 
the  power  of  the  apparatus  may  be  greatly  augmented.  Thin  wires  of  metal 
may  be  fused  and  dissipated ;  pieces  of  wood  may  be  shattered,  many  com- 
bustible substances  set  on  fire,  and  all  the  well-known  effects  of  lightning 
exhibited  upon  a  small  scale. 


ELECTRICITY. 


97 


Trie  electric  spark  is  often  very  conveniently  employed  in  chemical  inqui- 
ries for  firing  gaseous  mixtures  in  close  vessels.  A  small  Leyden  jar  charged 
by  the  machine  is  the  most  effective  contrivance  for  this  purpose,  but,  not 
unfrequently,  a  method  may  be  resorted  to  which  involves  less  preparation. 
This  is  by  the  use  of  the  electrophorus. 

A  round  tray  or  dish  of  tinned  plate  is  ^ig-  68. 

prepared  (fig.  68),  having  a  stout  wire 
round  its  upper  edge ;  the  width  may  be 
about  twelve  inches,  and  the  depth  half 
an  inch.  This  tray  is  filled  with  melted 
shellac,  and  the  surface  rendered  as  even 
as  possible.  A  brass  disc,  with  rounded 
edge,  of  about  nine  inches  diameter,  is 
also  provided,  and  fitted  with  an  insulating 
handle.  When  a  spark  is  wanted,  the 
resinous  plate  is  excited  by  striking  with 

a  dry,  warm  piece  of  fur,  or  a  silk  handkerchief;  the  cover  is  placed  upon 
it,  and  touched  by  the  finger.  When  the  cover  is  raised,  it  is  found  so 
strongly  charged  by  induction  with  positive  electricity,  as  to  give  a  bright 
spark;  and,  as  the  resin  is  not  discharged  by  the  cover,  which  merely 
touches  it  at  a  few  points,  sparks  may  be  drawn  as  often  as  may  be  wished. 
It  is  not  known  to  what  cause  the  disturbance  of  the  electrical  equilibrium 
of  the  atmosphere  is  due ;  experiment  has  shown  that  the  higher  regions  of 
the  air  are  usually  in  a  positive  state,  the  intensity  of  which  reaches  a  maxi- 
mum at  a  particular  period  of  the  day.  In  cloudy  and  stormy  weather  the 
distribution  of  the  atmospheric  electiicity  becomes  much  deranged,  clouds 
near  the  surface  of  the  earth  often  appearing  in  a  negative  state. 

The  circumstances  of  a  thunder-storm  exactly  resemble  those  of  the 
charge  and  discharge  of  a  coated  plate  or  jar;  the  cloud  and  the  earth  repre- 
sent the  two  coatings,  and  the  intervening  air  the  bad-conducting  body  or 
dielectric.  The  polarities  of  the  opposed  surface  and  of  the  insulating  medium 
between  them  become  raised  by  mutual  induction,  until  violent  disruptive 
discharge  takes  place  through  the  air  itself,  or  through  any  other  bodies 
which  may  happen  to  be  in  the  interval.  When  these  are  capable  of  con- 
ducting freely,  the  discharge  is  silent  and  harmless ;  but  in  other  cases  it 
often  proves  highly  destructive.  These  dangerous  effects  are  now  in  a  great 
measure  obviated  by  the  use  of  lightning-rods  attached  to  buildings,  the 
erection  of  which,  however,  demands  a  number  of  precautions  not  always 
understood  or  attended  to.  The  masts  of  ships  may  be  guarded  in  like 
manner  by  metal  conductors ;  Sir  W.  Snow  Harris  has  devised  a  most  inge- 
nious plan  for  the  purpose,  which  is  now  adopted,  with  the  most  complete 
success,  in  the  British  Navy. 

When  two  solid  conducting  bodies  are  plunged  into  a  liquid  which  acts 
upon  them  unequally,  the  electric  equilibrium  is  also  disturbed,  the  one  ac- 
quiring the  positive  condition,  and  the  other  the  negative.  Thus,  pieces  of 
zinc  and  platinum  put  into  dilute  sulphuric  acid,  constitute  an  arrangement 
capable  of  generating  electrical  force  ;  the  zinc  being  the  metal  attacked, 
becomes  negative ;  and  the  platinum  remaining  unaltered,  assumes  the  posi- 
tive condition ;  and  on  making  a  metallic  communication  in  any  way  between 
the  two  plates,  discharge  ensues,  as  when  the  two  surfaces  of  a  coated  and 
charged  jar  are  put  into  connection. 

No  sooner,  however,  has  this  occurred,  than  the  disturbance  is  repeated , 
and  as  these  successive  charges  and  discharges  take  place  through  the  fluid 
and  metals  with  inconceivable  rapidity,  the  result  is  an  apparently  continuous 
action,  to  which  the  term  electrical  current  is  given. 

It  is  necessary  to  guard  against  the  idea  which  the  term  naturally  suggests, 
9 


9S 


ELECTRICITY 


Fig.  69. 


of  an  actual  bodily  transfer  of  siometliing  through  the  substance  of  the  con- 
ductors, like  water  through  a  pipe ;  the  real  nature  of  all  these  phenomena 
is  entirely  unknown,  and  may  perhaps  remain  so ;  the  expression  is  conve- 
nient notwithstanding,  and  consecrated  by  long  use ;  and  with  this  caution, 
the  very  dangerous  error  of  applying  figurative  language  to  describe  an 
effect,  and  then  seeking  the  nature  of  the  effect  from  the  common  meaning 
of  words,  may  be  avoided. 

The  intensity  of  the  electrical  excitement  developed  by  a  single  pair  of 
\netals  and  a  liquid,  is  too  feeble  to  affect  the  most  delicate  gold-leaf  elec- 
troscope ;  but,  by  arranging  a  number  of  such  alternations 
in  a  connected  series,  in  such  a  manner,  that  the  direction 
of  the  current  shall  be  the  same  in  each,  the  intensity 
may  be  very  greatly  exalted.  The  two  instruments  in- 
vented by  Volta,  called  the  pile,  and  crown  of  cups,  depend 
upon  this  principle. 

Upon  a  plate  of  zinc  (fig.  69)  is  laid  a  piece  of  cloth, 
rather  smaller  than  itself,  steeped  in  dilute  acid,  or  any 
liquid  capable  of  exerting  chemical  action  upon  the  zinc  ; 
upon  this  is  placed  a  plate  of  copper,  silver,  or  platinum  ; 
then  a  second  piece  of  zinc,  another  cloth,  and  plate  of 
inactive  metal,  until  a  pile  of  about  twenty  alternations 
has  been  built  up.  If  the  two  terminal  plates  be  now 
touched  with  wet  hands,  the  sensation  of  the  electric 
shock  will  be  experienced;  but,  unlike  the  momentary 
effect  produced  by  the  discharge  of  a  jar,  the  sensation 
will  be  prolonged  and  continuous,  and  with  a  pile  of  one  hundred  such  pairs, 
excited  by  dilute  acid,  it  will  be  nearly  insupportable.  When  such  a  pile  is 
insulated,  the  two  extremities  exhibit  strong  positive  and  negative  states,  and 
when  connection  is  made  between  them  by  wires  armed  with  points  of  hard 
charcoal  or  plumbago,  the  discharge  takes  place  in  the  form  of  a  bright  en- 
during spark  or  stream  of  fire. 

The  second  form  of  apparatus,  or  crown  of  cups,  is  precisely  the  same  in 
principle,  although  different  in  appearance.  A  nuryber  of  cups  or  glasses 
(fig.  70)  are  arranged  in  a  row  or  circle,  each  containing  a  piece  of  active  and 

Fig.  70. 


piece  of  inactive  metal,  and  a  portion  of  exciting  liquid ;  zinc,  copper,  and 
dilute  sulphuric  acid,  for  example.  The  copper  of  the  first  cup  is  connected 
with  the  zinc  of  the  second,  the  copper  of  the  second  with  the  zinc  of  the 
third,  and  so  to  the  end  of  the  series.  On  establishing  a  communication 
between  the  first  and  last  plates  by  means  of  a  wire,  or  otherwise,  discharge 
takes  place  as  before.  ,  . 

When  any  such  electrical  arrangement  consists  merely  of  a  single  pair  of 
conductors  and  an  interposed  liquid,  it  is  called  a  simple  circuit ;_  when  two 
or  more  alternations  arc  concerned,  the  term  "  compound  circuit "  i«  npplied  ; 
tJiey  are  called  also,  indifferently,  voltaic  batteries.     In  every  f<>~i»  of  such 


ELECTRICITY.  S9 

apparatus,  however  complex  it  may  appear,  the  direction  of  the  current  may 
be  easily  understood  and  remembered.  The  polarity  or  disturbance  may  be 
considered  to  commence  at  the  surface  of  the  metal  attacked,  and  to  be  pro- 
pagated through  the  liquid  to  the  inactive  conductor,  and  thence  back  again 
by  the  connecting  wire,  these  extremities  of  the  battery  being  always  re- 
spectively negative  and  positive  when  the  apparatus  is  insulated.  In  common 
parlance,  it  is  said  that  the  current  in  every  battery  in  an  active  state  starts 
from  the  metal  attacked,  passes  through  the  liquid  to  the  second  metal  or 
conducting  body,  and  returns  by  the  wire  or  other  channel  of  communica- 
tion ;  hence,  in  the  pile  and  crown  of  cups  just  described,  the  current  in  the 
battery  is  always  from  the  zinc  to  the  copper ;  and  out  of  the  battery,  from 
the  copper  to  the  zinc,  as  shown  by  the  arrows. 

In  the  modification  of  Volta's  original  pile,  made  by  Mr.  Cruikshank,  the 
zinc  and  copper  plates  are  soldered  together  and  cemented  water-tight  into. 
a  mahogany  trough  (fig.  71),  which  thus  becomes  divided  into  a  series  of 

Fig.  71. 


cells  or  compartments  capable  of  receiving  the  exciting  liquid.  This  appa- 
ratus is  well  fitted  to  exhibit  effects  of  tension,  to  act  upon  the  electroscope 
and  give  shocks ;  hence  its  advantageous  employment  in  the  application  of 
electricity  to  medicine,  as  a  very  few  minutes  suffices  to  prepare  it  for  use. 
The  crown  of  cups  was  also  put  into  a  much  more  manageable  form  by  Dr. 
Babington,  and  still  farther  improved,  as  will  hereafter  be  seen,  by  Dr. 
Wollaston.  Subsequently,  various  alterations  have  been  made  by  different 
experimenters  with  a  view  of  obviating  certain  defects  in  the  common  bat- 
teries, of  which  a  description  will  be  found  towards  the  middle  of  this 
volume. 

The  term  "galvanism,"  sometimes  applied  to  this  branch  of  electrical 
science,  is  used  in  honour  of  Professor  Galvani,  of  Bologna,  who,  in  1790, 
made  the  very  curious  observation  that  convulsions  could  be  produced  in  the 
limbs  of  a  dead  frog  when  certain  metals  were  made  to  touch  the  nerve  and 
muscle  at  the  same  moment.  It  was  Volta,  however,  who  pointed  out  thfe 
electrical  origin  of  these  motions,  and  although  the  explanation  he  offered 
of  the  source  of  the  electrical  disturbance  is  no  longer  generally  adopted, 
his  name  is  very  properly  associated  with  the  invaluable  instrument  his 
genius  gave  to  science. 

Th.  the  year  1822,  Professor  Seebeck,  of  Berlin,  discovered  another  source 
of  electricity,  to  which  allusion  has  already  been  made,  namely,  inequality 
of  temperature  and  conducting  power  in  different  metals  placed  in  contact, 
or  in  the  same  metal  in  different  states  of  compression  and  density.  Even 
with  a  great  number  of  alternations,  the  current  produced  is  exceedingly 
feeble  compared  with  that  generated  by  the  voltaic  pile. 

Two  or  three  animals  of  the  class  of  fishes,  as  the  torpedo,  or  electric  ray^ 
and  the  electric  eel  of  South  America,  are  furnished  with  a  special  organ  or 
apparatus  for  developing  electrical  force,  which  is  employed  in  defence,  or 
in  the  pursuit  of  prey.  Electricity  is  here  seen  to  be  closely  connected  with 
nervous  power ;  the  shock  is  given  at  the  will  of  the  animal,  and  great  ex- 
haustion follows  repeated  exertion  of  the  power. 

Although  the  fact  that  electricity  is  capable,  under  certain  circumstances, 
both  of  inducing  and  of  destroying  magnetism,  has  long  been  known,  from 


100  ELECTRICITY. 

the  effects  of  lightning  on  the  compass-needle  and  npon  small  steel  articles, 
as  knives  and  forks,  to  which  polarity  has  suddenly  been  given  by  the  stroke, 
it  was  not  until  1819  that  the  laws  of  these  phenomena  were  discovered  by 
Professor  (Ersted,  of  Copenhagen,  and  shortly  afterwards  fully  developed  by 
M.  Ampere. 

The  action  which  a  current  of  electricity,  from  whatever  source  proceed- 
ing, exerts  upon  a  magnetized  needle  is  quite  peculiar.  The  poles  or  centres 
of  magnetic  force  are  neither  attracted  nor  repelled  by  the  wire  carrying  the 
current,  but  made  to  move  around  the  latter,  by  a  force  which  may  be 
termed  tangential,  and  which  is  exerted  in  a  direction  perpendicular  at  once 
to  that  of  the  current,  and  to  the  line  joining  the  pole  and  the  wire.  Both 
poles  of  the  magnet  being  thus  acted  upon  at  the  same  time,  and  in  contrary 
directions,  the  needle  is  forced  to  arrange  itself  across  the  current,  so  that 
its  axis,  or  the  line  joining  the  poles,  may  be  perpendicular  to  the  wire ;  and 
this  is  always  the  position  which  the  needle  will  assume  when  the  influence 
of  terrestrial  magnetism  is  in  any  way  removed.  This  curious  angular  mo- 
tion may  even  be  shown  by  suspending  a  magnet  in  such  a  way  that  one  only 
of  its  poles  shall  be  subjected  to  the  current ;  a  permanent  movement  of 
rotation  will  continue  as  long  as  the  current  is  kept  up,  its  direction  being 
changed  by  altering  the  pole,  or  reversing  the  current.  The  moveable  con- 
nections are  made  by  mercury,  into  which  the  points  of  the  conducting-wires 
dip.  It  is  often  of  great  practical  consequence  to  be  able  to  predict  the 
direction  in  which  a  particular  pole  shall  move  by  a  given  cui-rent,  because 
in  all  galvanoscopes,  and  other  instruments  involving  these  principles,  the 
movement  of  the  needle  is  taken  as  an  indication  of  the  direction  of  the  cir- 
culating current.  And  this  is  easily  done  by  a  simple  mechanical  aid  to  the 
memory :  —  Let  the  current  be  supposed  to  pass  through  a  watch  from  the 
face  to  the  back ;  the  motion  of  the  north  pole  will  be  in  the  direction  of  the 
hands.     Or  a  little  piece  of  apparatus  (fig.  72)  may  be  used  if  reference  is 


Fig.  72. 


A 


"'""iiiiial         (s     '" iiiiiiiiBpi 


often  requiitfd;  this  is  a  piece  of  pasteboard,  or  other  suitable  material,  cut 
into  the  form  of  an  arrow  for  indicating  the  current,  crossed  by  a  magnet 
having  its  poles  marked,  and  arranged  in  the  true  position  with  respect  to 
the  current.  The  direction  of  the  latter  in  the  wire  of  the  galvanoscope  can 
at  once  be  known  by  placing  the  representative  magnet  in  the  direction 
assumed  by  the  needle  itself. 

The  common  galvanoscope,  consisting  of  a  coil  of  wire  having  a  compass- 
needle  suspended  on  a  point  within  it,  is  greatly  improved  by  the  addition 
of  a  second  needle,  as  already  in  part  described,  and  by  a  better  mode  of 
suspension,  a  long  fibre  of  silk  being  used  for  the  purpose.  The  two  needles 
are  of  equal  size  and  magnetized  as  nearly  as  possible  to  the  same  extent ; 
they  are  then  immovably  fixed  together,  parallel,  and  with  their  poles  op- 
posed, and  hung  with  the  lower  needle  in  the  coil  and  the  upper  one  above 
it.  The  advantage  gained  is  twofold;  the  system  is  asfa/ic,  unaffected,  or 
nearly  so,  by  the  magnetism  of  the  earth ;  and  the  needles  being  both  acted 
apon  in  the  same  manner  by  the  current,  are  urged  with  much  greater  force, 


ELECTRICITY. 


101 


than  «ne  aloile  would  be,  all  the  actions  of  every  part  of  the  coil  being 
strictly  concurrent.  A  divided  circle  is  placed  below  the  upper  needle,  by 
which  the  angular  motion  can  be  measured ;  and  the  whole  is  enclosed  in 
glass,  to  shield  the  needles  from  the  agitation  of  the  air.  The  arrangement 
is  shown  in  fig.  73, 


Fig.  73. 


rig.  74. 


The  action  between  the  pole  and  the  wire  is  mutual,  as  may  be  shown  by 
rendering  the  wire  itself  moveable  and  placing  a  magnet  in  its  vicinity  :  on 
completing  the  circuit,  the  wire  will  be  put  in  motion,  and,  if  the  arrange- 
ment permits,  rotate  around  the  magnetic  pole. 

A  little  consideration  will  show,  that,  from  the 
peculiar  nature  of  the  electro-dynamic  force,  a 
wire  carrying  a  current,  bent  into  a  spiral  or 
helix,  must  possess  the  properties  of  an  ordinary 
magnetized  bar,  its  extremities  being  attracted 
and  repelled  by  the  poles  of  a  magnet.  Such  is 
really  found  to  be  the  case,  as  may  be  proved  by  a 
variety  of  arrangements,  among  which  it  will  be 
*  sufficient  to  cite  the  beautiful  little  apparatus  of 
Professor  de  la  Rive.  —  A  short  wide  glass  tube 
(fig.  74)  is  fixed  into  a  cork  ring  of  considerable 
size  ;  a  little  voltaic  battery,  consisting  of  a  single 
pair  of  copper-  and  zinc  plates,  is  fitted  to  the  tube,  and  to  these  the  ends 
of  the  spiral  are  soldered.  On  filling  the  tube  with  dilute  acid  and  floating 
the  whole  in  a  large  basin  of  water,  the  helix  will  be  observed  to  arrange 
itself  in  the  magnetic  meridian,  and  on  trial  it  will  be  found  to  obey  a  mag- 
net held  near  it  in  the  most  perfect  manner,  as  long  as  the  current  circu 
lates. 

When  an  electric  current  is  passed  at  right  angles  to  a  piece  of  iron  oi- 
steel,  the  latter  acquires  magnetic  polarity,  either  temporary  or  permanent 
as  the  case  may  be,  the  direction  of  the  current  determining  the  position  of 
the  poles.  This  eflfect  is  prodigiously  increased  by  causing  the  current  to 
circulate  a  number  of  times  round  the  bar,  which  then  acquires  extraordi- 
nary magnetic  power.  A  piece  of  soft  iron,  worked  into  the  form  of  a  horse- 
shoe (fig.  75),  and  surrounded  by  a  coil  of  copper  wire  covered  with  silk  or 
cotton  for  the  purpose  of  insulation,  furnishes  an  excellent  illustration  of 
the  inductive  energy  of  the  current  in  this  respect ;  when  the  ends  of  the 
9  * 


102 


ELECTRICITY. 


Fig.  75. 


wire  are  put  into  communication  with  a  small  voltaic  battery  of  a  single  pair 
of  plates,  the  iron  instantly  becomes  so  highly  magnetic 
as  to  be  capable  of  sustaining  a  very  heavy  weight. 

A  current  of  electricity  can  thus  develop  magnetism 
in  &  ♦ransverse  direction  to  its  own ;  in  the  same  man- 
ner, magnetism  can  call  into  activity  electric  currents. 
If  the  two  extremities  of  the  coil  of  the  electro-magnet 
above  described  be  connected  with  a  galvanoscope,  and 
the  iron  magnetized  by  the  application  of  a  permanent 
Bteel  horse-shoe  magnet  to  the  ends  of  the  bar,  a  mo- 
mentary current  will  be  developed  in  the  wire,  and 
pointed  out  by  the  movement  of  the  needle.  It  lasts 
but  a  single  instant,  the  needle  returning  after  a  few  os- 
cillations to  a  state  of  rest.  On  removing  the  magnet, 
whereby  the  polarity  of  the  iron  is  at  once  destroyed,  a 
second  current  or  wave  will  become  apparent,  but  in  the 
opposite  direction  to  that  of  the  first.  By  employing  a 
very  powerful  steel  magnet,  surrounding  its  iron  keeper 
or  armature  with  a  very  long  coil  of  wire,  and  then 
making  the  armature  itself  rotate  in  front  of  the  faces 
of  the  magnet,  so  that  its  induced  polarity  shall  be 
rapidly  reversed,  magneto-electric  currents  may  be  pro- 
duced, of  such  intensity  as  to  give  bright  sparks  and  most  powerful  shocks, 
and  exhibit  all  the  phenomena  of  voltaic  electricity.  Fig.  76  represents  a 
very  powerful  arrangement  of  this  kind. 

Fig.  76. 


When  two  covereu  wires  are  twisted  together  or  laid  side  by  side  for  some 
distance,  and  a  current  transmitted  through  the  one,  a  momentary  electrical 
wave  will  be  induced  in  the  other  in  the  reverse  direction,  and  on  breaking 
oonnexion  with  the  battery,  a  second  single  wave  will  become  evident  by  the 
aid  of  the  galvanoscope,  in  the  same  direction  as  that  of  the  primary  cur- 
rent. In  the  same  way,  when  a  current  of  electricity  passes  through  one 
♦uru  in  a  ooil  of  wire,  it  induces  two  secondary  currents  in  all  the  other 


ELECTRICITY.  103 

turns  of  the  coil ;  when  the  circuit  is  closed,  the  first  is  moving  in  the  oppo- 
site direction  to  the  primary  current ;  the  second,  when  the  circuit  is  broken, 
has  a  motion  in  the  same  direction  as  the  primary  current.  The  effect  of 
the  latter  is  added  to  that  of  the  primary  current.  Hence,  if  a  wire  coil  be 
made  part  of  the  conducting  wire  of  a  weak  electric  pile,  and  if  the  primary 
current,  by  means  of  an  appropriate  arrangement,  is  made  and  broken  in 
rapid  succession,  we  can  increase  in  a  remarkable  manner  the  effects  which 
are  produced  at  the  moment  of  breaking  the  circuit  either  at  the  place  of 
interruption  —  such  as  the  spark-discharges ;  or  in  secondary  closing-con- 
ductors, such  as  the  action  on  the  nerves  or  the  decomposition  of  water. 

M.  Ampere  discovered  in  the  course  of  his  investigations  a  number  of 
extremely  interesting  phenomena  resulting  from  the  action  of  electrical  cur- 
rents on  each  other,  which  become  evident  when  arrangements  are  made  for 
giving  mobility  to  the  conducting  wires.  He  found  that,  when  two  currents 
flowiug  in  the  same  direction  were  made  to  approach  each  other,  strong 
attraction  took  place  between  them,  and  when  in  opposite  directions,  an 
equally  strong  repulsion.  —  These  effects,  which  are  not  difficult  to  demon- 
strate, have  absolutely  no  relation  that  can  be  traced  to  ordinary  electrical 
attractions  and  repulsions,  from  which  they  must  be  carefully  distinguished ; 
they  are  purely  dynamic,  having  to  do  with  electricity  in  motion.  M. 
Ampere  founded  upon  this  discovery  a  most  beautiful  and  ingenious  hypo- 
thesis of  magnetic  actions  in  general,  which  explains  very  clearly  the  influ- 
ence of  the  current  upon  the  needle. 

The  electricity  exhibited  under  certain  peculiar  circumstances  by  a  jet  of 
steam,  first  observed  by  mere  accident,  but  since  closely  investigated  by  Mr. 
Armstrong,  and  also  by  Mr.  Faraday,  is  now  referred  to  the  friction,  not  of 
the  pure  steam  itself,  but  of  particles  of  condensed  water,  against  the  inte- 
rior of  the  exit-tube.  It  is  very  doubtful  whether  mere  evaporation  can  cause 
electrical  disturbance,  and  the  hope  first  entertained  that  these  phenomena 
would  throw  light  upon  the  cause  of  electrical  excitement  in  the  atmosphere, 
is  now  abandoned.  The  steam  is  usually  positive,  if  the  jet-pipe  be  con- 
structed of  wood  or  clean  metal,  but  the  introduction  of  the  smallest  trace 
of  oily  matter  causes  a  change  of  sign.  The  intensity  of  the  charge  is, 
cceteris  paribus,  increased  with  the  elastic  force  of  the  steam.  By  this  means, 
effects  have  been  obtained  very  far  surpassing  those  of  the  most  powerful 
plate  electrical  machines  ever  constructed. 


PART  II. 

CHEMISTRY  OF  ELEMENTARY   BODIES. 


Thb  term  element  or  elementary  substance  is  applied  in  chemistry  to  those 
forms  or  modifications  of  matter  which  have  hitherto  resisted  all  attempts  to 
decompose  them.  Nothing  is  ever  meant  to  be  affirmed  concerning  their 
real  nature  ;  they  are  simply  elements  to  us  ai  the  present  time ;  hereafter, 
by  new  methods  of  research,  or  by  new  combinations  of  those  already  pos- 
sessed by  science,  many  of  the  substances  which  now  figure  as  elements  may 
possibly  be  shown  to  be  compounds ;  this  has  already  happened,  and  may 
again  take  place. 

The  elementary  bodies,  at  present  recognised,  amount  to  sixty-two  in 
number ;  of  these,  about  forty-seven  belong  to  the  class  of  metals.  Several 
of  these  are  of  recent  discovery  and  as  yet  very  imperfectly  known.  The 
distinction  between  metals  and  non-metallic  substances,  although  very  con- 
venient for  purposes  of  description,  is  entirely  arbitrary,  since  the  two  classes 
graduate  into  each  other  in  the  most  complete  manner. 

It  will  be  proper  to  commence  with  the  latter  and  least  numerous  division. 
The  elements  are  named  as  in  the  subjoined  table,  which,  however,  does  not 
indicate  the  order  in  which  they  will  be  discussed. 


Non-metallic 
Elements. 

MetalB. 

Oxygen 

Antimony 

Gold 

Barium 

Hydrogen 

Chromium 

Aluminium 

Strontium 

Nitrogen 

Vanadium 

Beryllium 

Calcium 

Chlorine  ^ 

Tungsten 

(or  Glucinum) 

Magnesium 

Iodine   ^ 

(or  Wolfram) 

Zirconium 

Zinc 

Bromine  ^ 

Molybdenum 

Norium 

Cadmium 

Fluorine 

Tantalum 

Thorium 

Nickel 

Carbon  - 

(or  Columbium) 

Yttrium 

Cobalt 

Silicon  . 

Niobium 

Cerium 

Copper 

Boron 

Pelopium 

Erbium 

Iron 

Sulphur 

Titanium 

Terbium 

Manganese 

Selenium  - 

Uranium 

Lantanum 

Lithium 

Phosphorus 

Platinum 

Didymium 

Sodium 

Palladium 

Bismuth 

Potassium 

Elements  of  interme- 
diate characters. 

Rhodium 
Iridium 

Tin 
Mercury 

Arsenic 

Ruthenium 

Silver 

Telluriuff 

Osmium 

Lead 

(104) 


OXYGEN, 


im 


ox  YO  EN. 

Whatever  plan  of  classification,  founded  on  the  natural  relations  of  the 
elements,  be  adopted,  in  the  practical  study  of  chemistry,  it  will  always  be 
found  most  advantageous  to  commence  with  the  consideration  of  the  great 
constituents  of  the  ocean  and  the  atmosphere. 

Oxygen  was  discovered  in  the  year  1774,  by  Scheele,  in  Sweden,  and  Dr. 
Priestley,  in  England,  independently  of  each  other,  and  described  under  the 
terms  empyreal  air  and  dephlogisticated  air.  The  name  oxygen '  was  given  to 
it  by  Lavoisier  some  time  afterwards.  Oxygen  exists  in  a  free  and  uncom- 
bined  state  in  the  atmosphere,  mingled  with  another  gaseous  body,  nitrogen  : 
no  good  direct  means  exist,  however,  for  separating  it  from  the  latter,  and, 
accordingly,  it  is  always  obtained  for  purposes  of  experiment  by  decom- 
posing certain  of  its  compounds,  which  are  very  numerous. 

The  red  oxide  of  mercury,  or  red  precipitate  of  the  old  writers,  may  be 
employed  with  this  view.  In  this  substance,  the  attraction  which  holds  to- 
gether the  mercury  and  the  oxygen  is  so  feeble,  that  simple  exposure  to  heat 
suffices  to  bring  about  decomposition.  The  red  precipitate  is  placed  in  a 
short  tube  of  hard  glass,  to  which  is  fitted  a  perforated  cork,  furnished  with 
a  piece  of  narrow  glass  tube,  bent  as  in  the  figure.  The  heat  of  a  spirit- 
lamp  being  applied  to  the  substance,  decomposition  speedily  commences, 
globules  of  metallic  mercury  collect  in  the  cool  part  of  the  wide  tube,  which 
answers  the  purpose  of  a  retort,  while  gas  issues  in  considerable  quantity  from 
the  apparatus.  This  gas  is  collected  and  examined  by  the  aid  of  the  pneu- 
matic trough,  which  consists  of  a  vessel  of  water  provided  with  a  shelf,  upon 
which  stand  the  jars  or  bottles  destined  to  receive  the  gas,  filled  with  water 
and  inverted.  By  keeping  the  level  of  the  liquid  above  the  mouth  of  the  jar, 
the  water  is  retained  in  the  latter  by  the  pressure  of  the  atmosphere,  and 
entrance  of  air  is  prevented.  When  brought  over  the  extremity  of  the  gas- 
delivering  tube,  the  bubbles  of  gas  rising  through  the  water  collect  in  the 
upper  part  of  the  jar  and  displace  the  liquid.     As  soon  as  one  jar  is  filled^ 

Fig.  77. 


From  ^(uf,  acid,  and  ycvvdia,  I  i^ve  rise  to. 


UQ 


OXYGEN 


it  may  be  removed,  still  keeping  its  mouth  below  the  water-level,  and  an- 
other substituted.     The  whole  arrangement  is  shown  in  fig.  77. 

The  experiment  described  is  more  instructive  as  an  excellent  case  of  the 
resolution  by  simple  means  of  a  compound  body  into  its  constituents,  than 
valuable  as  a  source  of  oxygen  gas.  A  better  and  more  economical  method 
is  to  expose  to  heat  in  a  retort,  or  flask  furnished  with  a  bent  tube,  a  por- 
tion of  the  salt  called  chlorate  of  potassa.  A  common  Florence  flask  serves 
perfectly  well,  the  heat  of  a  spirit-lamp  being  sufiicient.  The  salt  melts 
and  decomposes  with  ebullition,  yielding  a  very  large  quantity  of  oxygen 
gas,  which  may  be  collected  in  the  way  above  described.  The  first  portion 
of  the  gas  often  contains  a  little  chlorine.  The  white  saline  residue  in  the 
flask  is  chloride  of  potassium.  This  plan,  which  is  very  easy  of  execution, 
is  always  adopted  when  very  pure  gas  is  required  for  analytical  purpose. 

A  third  method,  very  good  when  perfect  purity  is  not  demanded,  is  to  heat 
to  redness,  in  an  iron  retort  or  gun-barrel,  the  black  oxide  of  manganese  of 
commerce,  which  under  these  circumstances  sufi'ers  decomposition,  although 
not  to  the  extent  manifest  in  the  red  precipitate. 

If  a  little  of  the  black  oxide  of  manganese  be  finely  powdered  and  mixed 
with  chlorate  of  potassa,  and  this  mixture  heated  in  a  flask  or  retort  by  a 
lamp,  oxygen  will  be  disengaged  with  the  utmost  facility,  and  at  a  far  lower 
temperature  than  when  the  chlorate  alone  is  used.  All  the  oxygen  comes 
from  the  chlorate,  the  manganese  remaining  quite  unaltered.  The  materials 
should  be  well  dried  in  a  capsule  before  their  introduction  into  the  flask. 
This  experiment  affords  an  instance  of  an  effect  by  no  means  rare,  in  which 
a  body  seems  to  act  by  its  mere  presence,  without  taking  any  obvious  part 
in  the  change  brought  about. 

Whatever  method  be  chosen — and  the  same  remark  applies  to  the  collec- 
tion of  all  othef  gases  by  similar  means — the  first  portions  of  gas  must  be 
suffered  to  escape,  or  be  received  apart,  as  they  are  contaminated  by  the  at- 
mospheric air  of  the  apparatus.  The  practical  management  of  gases  is  a 
pomt  of  great  importance  to  the  chemical  student,  and  one  with  which  he 
must  endeavour  to  familiarize  himself  The  water-trough  just  described  is 
one  of  the  most  indispensable  articles  of  the  laboratory,  and  by  its  aid  all 
experiments  on  gases  are  carried  on  when  the  gases  themselves  are  not  sen- 
sibly acted  upon  by  water.  The  trough  is  best  constructed  of  japanned 
copper,  the  form  and  dimensions  being  regulated  by  the  magnitude  of  the 
jars.  It  should  have  a  firm  shelf,  so  arranged  as  to  be  always  about  an  inch 
below  the  level  of  the  water,  and  in  the  shelf  a  groove  should  be  made 
about  half  an  inch  in  width,  and  the  same  in  depth,  to  admit  the  extremity 
i)f  the  delivery-tube  beneath  the  jar,  which  stands  securely  upon  the  shelf. 

Fig.  78. 


OXYGEN. 


107 


Fig.  79. 


When  the  pneumatic  trough  is  required  of  tolerably  large  dimensions,  it  maj 
with  great  advantage  have  the  form  and  disposition  represented  in  the  cux 
(fig.  78) ;  one  end  of  the  groove  spoken  of,  which  crosses  the  shelf  or  shallow 
portion,  is  shown  at  a. 

Gases *are  transferred  from  jar  to  jar  with  the  utmost  facility,  by  firs* 
filling  the  vessel  into  which  the  gas  is  to  be  passed  with  water,  inverting  it, 
carefully  retaining  its  mouth  below  the  water-level,  and  then  bringing  be- 
neath it  the  aperture  of  the  jar  containing  the  gas.  On  gently  inclining  the 
latter,  the  gas  passes  by  a  kind  of  inverted  decantation  into  the  second 
vessel.  When  the  latter  is  narrow,  a  funnel  may  be  placed  loosely  in  its 
neck,  by  which  loss  of  gas  will  be  found  to  be  prevented. 

A  jar  wholly  or  pai'tially  filled  with  gas  at  the  pneumatic  trough  may  b 
removed  by  placing  beneath  it  a  shallow  basin, 
or  even  a  common  plate  (fig.  79),  so  as  to 
carry  away  enough  water  to  cover  the  edge  of 
the  jar;  and  gas,  especially  oxygen,  may  be 
so  preserved  for  many  hours  without  material 
injury. 

Gas-jars  are  often  capped  at  the  top,  and 
fitted  with  a  stop-cock  for  transferring  to  blad- 
ders or  caoutchouc  bags.  When  such  a  vessel 
is  to  be  filled  with  water,  it  may  be  slowly 
sunk  in  an  upright  position  in  the  well  of  the 
pneumatic  trough,  the  stop-cock  being  open  to 
allow  the  air  to  escape,  until  the  water  reaches 
the  brass  cap.  The  cock  is  then  to  be  turned, 
and  the  jar  lifted  upon  the  shelf  and  filled  with 
gas  in  the  usual  way.  If  the  trough  be  not 
deep  enough  for  this  manoeuvre,  the  mouth 
may  be  applied  to  the  stop-cock,  and  the  vessel 

filled  by  sucking  out  the  air  until  the  water  rises  to  the  cap.  In  all  cases  it 
is  proper  to  avoid  as  much  as  possible  wetting  the  stop-cocks,  and  other  brass 
apparatus. 

Mr.  Pepys  contrived  some  years  ago  an  admirable  piece  of  apparatus  for 
storing  and  retaining  large  quantities  of  gas. 
It  consists  of  a  drum  or  reservoir  of  sheet 
copper  (fig.  80),  surmounted  by  a  shallow 
trough  or  cistern,  the  communication  be- 
tween the  two  being  made  by  a  couple  of 
tubes,  a  b,  furnished  with  cocks,  fh,  one  of 
which  passes  nearly  to  the  bottom  of  the 
drum,  as  shown  in  the  sectional  sketch.  A 
short  wide  open  tube,  c,  is  inserted  obliquely 
near  the  bottom  of  the  vessel,  into  which  a 
plug  may  be  tightly  screwed.  A  stop-cock, 
ff,  near  the  top,  serves  to  transfer  gas  to  a 
bladder  or  tube  apparatus.  A  glass  water- 
guage,  de,  affixed  to  the  side  of  the  drum, 
and  communicating  with  both  top  and  bot- 
tom, indicates  the  level  of  the  liquid  within. 

To  use  the  gas-holder,  the  plug  is  first  to 
be  screwed  into  the  lower  opening,  and  the 
drum  completely  filled  with  water.  AH 
three  stop-cocks  are  then  to  be  closed,  and 
the  plug  removed.  The  pressure  of  the  atmosphere  retains  the  water  in  the 
gas  holder,  and  if  no  air-leakage  occur,  the  escape  of  water  is  inconsider- 


Fig.  80. 


108  OXYGEN. 

able.  The  extremity  of  the  delivery-tube  is  now  to  be  well  pushed  through 
the  open  aperture  into  the  drum,  so  that  the  bubbles  of  gas  rise  without  hin- 
drance to  the  upper  part,  displacing  the  water,  which  flows  out  in  the  same 
proportion  into  a  vessel  placed  for  its  reception.  When  the  drum  is  filled,  or 
enough  gas  has  been  collected,  the  tube  is  withdrawn,  and  the  plug  screwed 
into  its  place. 

When  a  portion  of  the  gas  is  to  be  transferred  to  a  jar,  the  latter  is 
filled  with  water  at  the  pneumatic  trough,  carried  by  the  help  of  a  basin  or 
plate  to  the  cistern  of  the  gas-holder,  and  placed  over  the  shorter  tube.  Oi 
opening  the  cock  of  the  neighbouring  tube,  the  hydrostatic  pressure  of  th « 
column  of  water  will  cause  condensation  of  the  gas,  and  increase  its  elastic 
force,  so  that  on  gently  turning  the  cock  beneath  the  jar,  it  will  ascend  into 
the  latter  in  a  rapid  stream  of  bubbles.  The  jar,  when  filled,  may  again 
have  the  plate  slipped  beneath  it,  and  be  removed  without  difl&culty. 

Oxygen,  when  free  or  uncombined,  is  only  known  in  the  gaseous  state,  all 
attempts  to  reduce  it  to  the  liquid  or  solid  condition  by  cold  and  pressure 
having  completely  failed.  It  is,  when  pure,  colourless,  tasteless,  and  in- 
odorous ;  it  is  the  sustaining  principle  of  animal  life,  and  of  all  the  ordinary 
phenomena  of  combustion 

Bodies  which  burn  in  the  air  burn  with  greatly  increased  splendour  in 
oxygen  gas.  If  a  taper  be  blown  out,  and  then  introduced  while  the  wick 
remains  red-hot,  it  is  instantly  rekindled :  a  slip  of  wood  or  a  match  is  re- 
lighted in  the  same  manner.  This  effect  is  highly  characteristic  of  oxygen, 
there  being  but  one  other  gas  which  possesses  the  same  property ;  and  this 
is  easily  distinguished  by  other  means.  The  experiment  with  the  match  is 
also  constantly  used  as  a  rude  test  of  the  goodness  of  the  gas  when  it  is  about 
to  be  collected  from  the  retort,  or  when  it  has  stood  some  time  in  contact 
with  water  exposed  to  air. 

When  a  bit  of  charcoal  is  aflBxed  to  a  wire,  and  plunged  with  a  single 
point  red-hot  into  a  jar  of  oxygen,  it  burns  with  great  brilliancy,  throwing 
off  beautiful  scintillations,  until,  if  the  oxygen  be  in  excess,  it  is  completely 
consumed.  An  iron  wire,  or,  still  better,  a  steel  watch-spring,  armed  at  its 
extremity  with  a  bit  of  lighted  amadou,  and  introduced  into  a  vessel  of  good 
gas,  exhibits  a  most  beautiful  appearance  of  combustion.  If  the  experiment 
be  made  in  a  jar  standing  on  a  plate,  the  fused  globules  of  black  oxide  of 
iron  fix  themselves  in  the  glaze  of  the  latter,  after  falling  through  a  stratum 
of  water  half  an  inch  in  depth.  Kindled  sulphur  burns  with  great  beauty 
in  oxygen,  and  phosphorus,  under  similar  circumstances,  exhibits  a-feplendour 
which  the  eye  is  unable  to  support. 

In  these  and  many  other  similar  cases  which  might  be  mentioned,  the  same 
ultimate  effect  is  produced  as  in  atmospheric  air ;  the  action  is,  however, 
more  energetic  from  the  absence  of  the  gas  which  in  the  air  dilutes  the 
oxygen,  and  enfeebles  its  chemical  powers.  The  process  of  respiration  in  ani- 
mals is  an  effect  of  the  same  nature  as  common  combustion.  The  blood  con- 
tains substances  which  slowly  burn  by  the  aid  of  the  oxygen  thus  introduced 
into  the  system.     When  this  action  ceases,  life  becomes  extinct. 

Oxygen  is,  bulk  for  bulk,  a  little  heavier  than  atmospheric  air,  which  is 
usually  taken  as  the  standard  of  unity  of  specific  gravity  among  gases.  Its 
specific  gravity  is  expressed  by  the  number  1-1057;  •  100  cubic  inches  at  60° 
(15°-5C).  and  under  the  mean  pressure  of  the  atmosphere,  that  is,  30  inches 
of  mercury,  weigh  34-29  grains. 

It  has  been  already  remarked,  that  to  determine  with  the  last  degree  of 
accuracy  the  specific  gravity  of  a  gas,  is  an  operation  of  very  great  practical 
iiflBculty,  but  at  the  same  time  of  very  great  importance.    There  are  several 

»  Dumas,  Ann.  Chiin.  et  Phys.,  3d  series,  iii.  275. 


OXYGEN.  109 

methods  which  may  be  adopted  for  this  purijose ;  the  one  below  described 
appears,  on  the  whole,  to  be  the  simplest  and  best.  It  requires,  however, 
the  most  scrupulous  care,  and  the  observance  of  a  number  of  minute  pre- 
cautions, which  are  absolutely  indispensable  to  success. 

The  plan  of  the  operation  is  as  follows :  A  large  glass  globe  is  to  be  filled 
with  the  gas  to  be  examined,  in  a  perfectly  pure  and  dry  state,  having  a 
known  temperature,  and  an  elastic  force  equal  to  that  of  the  atmosphere  at 
the  time  of  the  experiment.  The  globe  so  filled  is  to  be  weighed.  It  is 
then  to  be  exhausted  at  the  air-pump  as  far  as  convenient,  and  again 
weighed.  Lastly,  it  is  to  be  filled  with  dry  air,  the  temperature  and  pres- 
sure of  which  are  known,  and  its  weight  once  more  determined.  On  the 
supposition  that  the  temperature  and  elasticity  are  the  same  in  both  cases, 
the  specific  gravity  is  at  once  obtained  by  dividing  the  weight  of  the  gas  by 
that  of  the  air. 

The  globe  or  flask  must  be  made  very  thin,  and  fitted  with  a  brass  cap, 
surmounted  by  a  small  but  excellent  stop-cock.  A  delicate  thermometer 
should  be  placed  in  the  inside  of  the  globe,  secured  to  the  cap.  The  gas 
must  be  generated  at  the  moment,  and  conducted  at  once  into  the  previously 
exhausted  vessel,  through  a  long  tube  filled  Avith  fragments  of  pumice  moist- 
ened with  oil  of  vitriol,  or  some  other  extremely  hj'groscopic  substance,  by 
which  it  is  freed  from  all  moisture.  As  the  gas  is  necessarily  generated 
under  some  pressure,  the  elasticity  of  that  contained  in  the  filled  globe  will 
slightly  exceed  the  pressure  of  the  atmosphere ;  and  this  is  an  advantage, 
since  by  opening  the  stop-cock  for  a  single  instant  when  the  globe  has 
attained  an  equilibrium  of  temperature,  the  tension  becomes  exactly  that  of 
the  air,  so  that  all  barometrical  correction  is  avoided,  unless  the  pressure  of 
the  atmosphere  should  sensibly  vary  during  the  time  occupied  by  the  expe- 
riment. It  is  hardly  necessary  to  remark,  that  the  greatest  care  must  also 
be  taken  to  purify  and  dry  the  air  used  as  the  standard  of  comparison,  and 
to  bring  both  gas  and  air  as  nearly  as  possible  to  the  same  temperature,  to 
obviate  the  necessity  of  a  correction,  or  at  least  to  diminish  almost  to  nothing 
the  errors  involved  by  such  a  process. 

The  compounds  formed  by  the  direct  union  of  oxygen  with  other  bodies, 
bear  the  general  name  of  oxides ;  these  are  very  numerous  and  important. 
They  are  conveniently  divided  into  three  principal  groups  or  classes.  The 
first  division  contains  all  those  oxides  which  resemble  in  their  chemical  rela- 
tions, potassa,  soda,  or  the  oxide  of  silver  or  of  lead ;  these  are  denominated 
alkaline  or  basic  oxides,  or  sometimes  salifiable  bases.  The  oxides  of  the 
second  group  have  properties  exactly  opposed  to  those  of  the  bodies  men- 
tioned ;  oil  of  vitriol  and  phosphoric  acid  may  be  taken  as  the  types  or  repre- 
sentatives of  the  class :  they  are  called  acids,  and  tend  strongly  to  unite 
with  the  basic  oxides.  When  this  happens,  what  is  called  a  salt  is  generated 
as  sulphate  of  potassa,  or  phosphate  of  silver,  each  of  these  substances  be- 
ing compounded  of  a  pair  of  oxides,  one  of  which  is  highly  basic  and  the 
other  highly  acid. 

Then  there  remains  a  third  group  of  what  may  be  termed  neutral  oxides, 
from  their  little  disposition  to  enter  into  combination.  The  black  oxide  of 
manganese,  already  mentioned,  is  an  excellent  example. 

It  very  frequently  happens  that  a  body  is  capable  of  uniting  with  oxygen 
in  several  proportions,  forming  a  series  of  oxides,  to  which  it  is  necessary 
to  give  distinguishing  names.  The  rule  in  such  cases  is  very  simple,  at  least 
when  the  oxides  of  the  metals  are  concerned.  In  such  a  series  it  is  always 
found  that  one  out  of  the  number tias  a  strongly-marked  basic  character;  to 
this  the  term  protoxide  is  given.  The  compounds  next  succeeding  receive 
the  names  of  binoxide  or  dentoxide,  teroxide  or  tritoxide,  &c.,  from  the  Latin  or 
Greek  numerals,  the  difrerent  grades  of  oxidation  being  thus  indicated.  If 
10 


110  HYDROGEN. 

ther-*  be  a  compound  between  the  protoxide  and  binoxide,  the  name  sesqui- 
oxiai  is  usually  applied.  So  it  is  usual  to  call  the  highest  oxide,  not  having 
distinctly  acid  characters,  peroxide,  from  the  Latin  prefix,  signifying  excess. 
Any  compound  containing  less  oxygen  than  the  protoxide,  is  called  a  sub- 
oxide. Superoxide  or  hyperoxide  are  words  sometimes  used  instead  of  per- 
oxide. 

Ozone.  —  It  has  long  been  known  that  dry  oxygen,  or  atmospherio  air, 
when  exposed  to  the  passage  of  a  series  of  electric  sparks,  emits  a  peculiar 
and  somewhat  metallic  odour.  The  same  odour  may  be  imparted  to  moist 
oxygen,  by  allowing  phosphorus  to  remain  for  some  time  in  it.  A  more 
accurate  examination  of  this  odorous  air  has  shown  that,  in  addition  to  the 
smell,  it  assumes  several  properties  not  exhibited  by  pure  oxygen.  One  of 
its  most  curious  effects  is  the  liberation  of  iodine  from  iodide  of  potassium. 
The  oxygen  thus  altered  has  been  the  subject  of  many  researches  lately, 
particularly  by  Prof.  Schoenbein,  of  Basel,  who  proposed  the  name  of  ozone » 
for  it.  The  true  nature  of  ozone,  however,  is  still  unknown,  most  probably 
it  is  a  peculiar  modification  of  oxygen. 

HYDKOGBN. 

Hydrogen  is  always  obtained  for  experimental  purposes  by  deoxidizing 
water,  of  which  it  forms  the  characteristic  component.' 

If  a  tube  of  iron  or  porcelain,  containing  a  quantity  of  filings  or  turnings 
of  iron,  be  fixed  across  a  furnace,  and  its  middle  portion  be  made  red-hot, 
and  then  the  vapour  of  water  transmitted  over  the  heated  metal,  a  large 
quantity  of  permanent  gas  will  be  disengaged  from  the  tube,  and  the  iron 
will  become  converted  into  oxide,  and  acquire  an  increase  in  weight.  The 
gas  is  hydrogen ;  it  may  be  collected  over  water  and  examined. 

When  zinc  is  put  into  water,  chemical  action  of  the  liquid  upon  the  metal 
is  imperceptible ;  but  if  a  little  sulphuric  acid  be  added,  decomposition  of 
the  water  ensues,  the  oxygen  unites  with  the  zinc,  forming  oxide  of  zinc, 
which  is  instantly  dissolved  by  the  acid,  while  the  hydrogen,  previously  in 
union  with  the  oxygen,  is  disengaged  in  the  gaseous  form.  The  reaction  is 
represented  in  the  subjoined  diagram. 

Water  /Hydrogen Free. 

(  Oxygen 

Zinc ~ oxide  of  zinc  ^  Sulphate  of 

Sulphuric  acid j  oxide  of  zinc 

It  is  not  easy  to  explain  the  fact  of  the  ready  decomposition  of  water  by 
zinc,  in  presence  of  an  acid  or  other  substance  which  can  unite  with  the 
oxide  so  produced ;  it  is,  however,  a  kind  of  reaction  of  very  common  oc- 
currence in  chemistry. 

The  simplest  method  of  preparing  the  gas  is  the  following. — A  wide-necked 
bottle  is  chosen,  and  fitted  with  a  sound  cork  (fig.  81).  perforated  by  two 
holes  for  the  reception  of  a  small  tube-funnel  reaching  nearly  to  the  bottom 
of  the  bottle,  and  a  piece  of  bent  glass  tube  to  convey  away  the  disengaged 
gas.  Granulated  zinc,  or  scraps  of  the  malleable  metal,  are  put  into  the 
bottle,  together  with  a  little  water,  and  sulphuric  acid  slowly  added  by  the 
funnel,  the  point  of  which  should  dip  into  the  liquid.  The  evolution  of  gas 
is  easily  regulated  by  the  supply  of  acid,  and  when  enough  has  been  dis- 
charged to  expel  the  air  of  the  vessel,  it  may  be  collected  over  water  into  a 
jar,  or  passed  into  a  gas-holder.  In  the  absence  of  zinc,  filings  of  iron  or 
small  nails  may  be  used,  but  with  less  advantage. 

»  From  S^w,  I  smell. 

'  Hence  the  name,  from  u^wfi,  water,  and  ytwaw. 


HYDROGEN, 


111 


Iig.81. 


A  little  practice  will  soon  enable  the 
pupil  to  construct  and  arrange  a  variety 
of  useful  forms  of  apparatus,  in  which 
bottles  and  other  articles  always  at 
hand,  are  made  to  supersede  more 
costly  instruments.  Glass  tube,  pur- 
chased by  weight  of  the  maker,  may  be 
cut  by  scratching  with  a  file,  and  then 
applying  a  little  force  with  both  hands. 
It  may  be  softened  and  bent,  when  of 
small  dimensions,  by  the  flame  of  a 
epirit-lamp,  or  even  a  candle  or  gas-jet. 
Corks  may  be  perforated  by  a  heated 
wire,  and  the  hole  rendered  smooth  and 
cylindrical  by  a  round  file,  or  the  in- 
genious cork-borer  of  Dr.  Mohr,  now 
to  be  had  of  most  instrument  makers, 
may  be  used  instead.  Lastly,  in  the 
event  of  bad  fitting,  or  unsoundness  in 
the  cork  itself,  a  little  yellow  wax 
melted  over  the  surface,  or  even  a  little  grease  applied  with  the  finger, 
renders  it  sound  and  air-tight,  when  not  exposed  to  heat. 

Hydrogen  is  colourless,  tasteless,  and  inodorous,  when  quite  pure.  To 
obtain  it  in  this  condition,  it  must  be  prepared  from  the  purest  zinc  that  can 
be  obtained,  and  passed  in  succession  through  solutions  of  potassa  and  nitrate 
of  silver.  When  prepared  from  commercial  zinc,  it  has  a  slight  smell,  which 
is  due  to  impurity,  and  when  iron  has  been  used,  the  odour  becomes  very 
strong  and  disagreeable.  It  is  inflammable,  burning  when  kindled  with  a 
pale  yellowish  flame,  and  evolving  much  heat,  but  very  little  light.  The 
result  of  the  combustion  is  water.  It  is  even  less  soluble  in  water  than 
oxygen,  and  has  never  been  liquefied.  Although  destitute  of  poisonous  pro- 
perties, it  is  incapable  of  sustaining  life. 

In  point  of  specific  gravity,  hydrogen  is  the  lightest  substance  known ; 
Dumas  and  Boussingault  place  its  density  between  0-0691  and 
0-0695 ;  *   hence  100  cubic  inches  will  weigh,  under  ordinary 
circumstances  of  pressure  and  temperature,  2-14  grains. 

When  a  gas  is  much  lighter  or  much  heavier  than  atmospheric 
air,  it  may  often  be  collected  and  examined  without  the  aid  of 
the  pneumatic  trough.  A  bottle  or  narrow  jar  may  be  filled 
with  hydrogen  without  much  admixture  of  air,  by  inverting  it 
over  the  extremity  of  an  upright  tube  delivering  the  gas  (fig. 
82).  In  a  short  time,  if  the  supply  be  copious,  the  air  will 
be  wholly  displaced  and  the  vessel  filled.  It  may  now  be 
removed,  the  vertical  position  being  carefully  retained,  and 
closed  by  a  stopper  or  glass  plate.  If  the  mouth  of  the  jar  be 
wide,  it  must  be  partially  closed  by  a  piece  of  card-board 
during  the  operation.  This  method  of  collecting  gases  by 
displacement  is  often  extremely  useful.  Hydrogen  was  for- 
merly used  for  filling  air-balloons,  being  made  for  the  purpose 
on  the  spot  from  zinc  or  iron  and  dilute  sulphuric  acid.  Its  use 
is  now  superseded  by  that  of  coal-gas,  which  may  be  made  very  light  by 
employing  a  high  temperature  in  the  manufacture.  Although  far  inferior 
to  pure  hydrogen  in  buoyant  power,  it  is  found  in  practice  to  possess  advan- 
tages over  that  substance,  whUe  its  greater  density  is  easily  TompensateJ 
by  increasing  the  magnitude  of  the  balloon. 


Fig.  82. 


*  Ann.  Cliira.  et  Phys.  3d.  series,  viii.  Ail. 


Vl^  HYDROGEN. 

There  is  a  very  remarkable  property  enjoyed  by  gases  and  vapours  in 
general,  which  is  seen  in  a  high  degree  of  intensity  in  the  case  of  hydrogen  , 
this  is  what  is  called  diffusive  power.  If  two  bottles,  containing  gases  which 
do  not  act  chemically  upon  each  other  at  common  temperatures,  be  connected 
by  a  narrow  tube  and  left  for  some  time,  these  will  be  found,  at  the  expira- 
tion of  a  certain  period,  depending  much  upon  the  narrowness  of  the  tube 
and  its  length,  uniformly  mixed,  even  though  the  gases  differ  greatly  in 
density,  and  the  system  has  been  arranged  in  a  vertical  position,  with  the 
heaviest  gas  downwards.  Oxygen  and  hydrogen  can  thus  be  made  to  mix, 
in  a  few  hours,  against  the  action  of  gravity,  through  a  tube  a  yard  in  length, 
and  not  more  than  one-quarter  of  an  inch  in  diameter ;  and  the  fact  is  true 
of  all  other  gases  which  are  destitute  of  direct  action  upon  each  other. 

If  a  vessel  be  divided  into  two  portions  by  a  diaphragm  or  partition  of 
porous  earthenware  or  dry  plaster  of  Paris,  and  each  half  filled  with  a  dif- 
ferent gas,  diffusion  will  immediately  commence  through  the  pores  of  the 
dividing  substance,  and  will  continue  until  perfect  mixture  has  taken  place. 
All  gases,  however,  do  not  permeate  the  same  porous  body,  or,  in  other 
words,  do  not  pass  through  narrow  orifices  with  the  same  degree  of  facility. 
Professor  Graham,  to  wliom  we  are  indebted  for  a  very  valuable  investigation 
of  this  interesting  subject,  has  established  the  existence  of  a  very  simple 
relation  between  the  rapidity  of  diffusion  and  the  density  of  the  gas,  which 
is  expressed  by  saying  that  the  diffusive  power  varies  inversely  as  the  square 
root  of  the  density  of  the  gas  itself.  Thus,  in  the  experiment  supposed,  if 
one  half  of  the  vessel  be  filled  with  hydrogen  and  the 
Fig.  83.  other  half  with  oxygen,  the  two  gases  will  penetrate  the 

diaphragm  at  very  different  rates  ;  four  cubic  inches  of  hy- 
drogen will  pass  into  the  oxygen  side,  while  one  cubic  inch 
of  oxygen  travels  in  the  opposite  direction.  The  densities 
of  the  two  gases  are  to  each  other  in  the  proportion  of  1  to 
16 ;  their  relative  rates  of  diffusion  will  be  inversely  as  the 
square  roots  of  these  numbers,  or  4  to  1. 

By  making  the  diaphragm  of  some  flexible  material,  as 
a  piece  of  membrane,  the  accumulation  of  the  lighter  gas 
on  the  side  of  the  heavier  may  be  rendered  evident  by  the 
bulging  of  the  membrane.  The  simplest  and  most  striking 
method  of  making  the  experiment  is  by  the  use  of  Profes- 
sor Graham's  diffusion-tube  (fig.  83),  This  is  merely  a 
piece  of  wide  glass  tube  ten  or  twelve  inches  in  length, 
having  one  of  its  extremities  closed  by  a  plate  of  plaster 
of  Paris  about  half  an  inch  thick,  and  well  dried.  When 
the  tube  is  filled  by  displacement  with  hydrogen,  and  then 
set  upright  in  a  glass  of  water,  the  level  of  the  liquid  rises 
in  the  tube  so  rapidly,  that  its  movement  is  apparent  to  the  eye,  and  speedily 
attains  a  height  of  several  inches  above  the  water  in  the  glass.  The  gas  is 
actually  rarefied  by  its  superior  diffusive  power  over  that  of  the  external 
air. 

It  is  impossible  to  over-estimate  the  importance  in  the  great  economy  of 
Nature,  of  this  very  curious  law  affecting  the  censtitution  of  gaseous  bodies ; 
it  is  the  principal  means  by  which  the  atmosphere  is  preserved  in  an  uniform 
jjtate,  and  the  accumulation  of  poisonous  gases  and  exhalations  in  towns  and 
other  confined  localities  prevented. 

A  distinction  must  be  carefully  drawn  between  real  diffusion  through  small 
apertures,  and  the  apparently  similar  passage  of  gas  through  wet  or  moist 
membranes  and  other  substances,  which  is  really  due  to  temporary  liquefac- 
tion or  solution  of  the  gas,  and  is  an  effect  completely  different  from  diffu- 
sion, properly  so  called.     For  example,  the  diffusive  power  of  carbonic  acid 


HYDROGEN.  113 

into  atmospheric  air  is  very  small,  but  it  passes  into  the  latter  through  a  wet 
bladder  with  the  utmost  ease,  in  virtue  of  its  solubility  in  the  water  with 
which  the  membrane  is  moistened.  It  is  by  such  a  process  that  the  function 
of  respiration  is  performed ;  the  aeration  of  the  blood  in  the  lungs,  and  the 
disengagement  of  the  carbonic  acid,  are  effected  through  wet  membranes ; 
the  blood  is  never  brought  into  actual  contact  with  the  air,  but  receives  its 
supply  of  oxygen,  and  disembarrasses  itself  of  carbonic  acid  by  this  kind 
of  spurious  diffusion. 

The  high  diffusive  power  of  hydrogen  against  air  renders  it  impossible  to 
retain  that  gas  for  any  length  of  time  in  a  bladder  or  caoutchouc  bag :  it  is 
even  unsafe  to  keep  it  long  in  a  gas-holder,  lest  it  should  become  mixed  with 
air  by  slight  accidental  leakage,  and  be  rendered  explosive.* 

It  has  been  stated,  that,  although  the  light  emitted  by  the  flame  of  pure 
hydrogen  is  exceedingly  feeble,  yet  the  temperature  of  the  flame  is  very 
high.  This  temperature  may  be  still  farther  exalted  by  previously  mixing 
the  hydrogen  with  as  much  oxygen  as  it  requires  for  combination,  that  is, 
as  will  presently  be  seen,  exactly  half  its  volume.  Such  a  mixture  burns 
like  gunpowder,  independently  of  the  external  air.  When  raised  to  the 
requisite  temperature  for  combination,  the  two  gases  unite  with  explosive 
violence.  If  a  strong  bottle,  holding  not  more  than  half  a  pint,  be  filled 
with  such  a  mixture,  the  introduction  of  a  lighted  match  or  red-hot  wire 
determines  in  a  moment  the  union  of  the  gases.  By  certain  precautions,  a 
mixture  of  oxygen  and  hydrogen  can  be  burned  at  a  jet  without  communi- 
cation of  fire  to  the  contents  of  the  vessel ;  the  flame  is  in  this  case  solid. 

A  little  consideration  will  show,  that  all  ordinary  flames  burning  in  the 
air  or  in  pure  oxygen  are,  of  necessity,  hollow.  The  act  of  combustion  is 
nothing  more  than  the  energetic  union  of  the  substance  burned  with  the 
surrounding  oxygen :  and  this  union  can  only  take  place  at  the  surface  of 
the  burning  body.  Such  is  not  the  case,  however,  with  the  flame  now  under 
consideration ;  the  combustible  and  the  oxygen  are  already  mixed,  and  only 
require  to  have  their  temperature  a  little  raised  to  cause  them  to  combine  in 
every  part.  The  flame  so  produced  is  very  different  in  phy- 
sical characters  from  that  of  a  simple  jet  of  hydrogen  or  any  ^'^'"  ^^• 
other  combustible  gas  ;  it  is  long  and  pointed,  and  very  re-  ^ 
markable  in  appearance. 

The  safety-jet  of  Mr.  Hemming,  the  construction  of  which 
involves  a  principle  not  yet  discussed,  may  be  adapted  to  a  com- 
mon bladder  containing  the  mixture,  and  held  under  the  arm, 
and  the  gas  forced  through  the  jet  by  a  little  pressure. 
Although  the  jet,  properly  constructed,  is  believed  to  be  safe, 
it  is  best  to  use  nothing  stronger  than  a  bladder,  for  fear  of 
injury  in  the  event  of  an  explosion.  The  gases  are  often  con- 
tained in  separate  reservoirs,  a  pair  of  large  gas-holders,  for 
example,  and  only  suffered  to  mix  in  the  jet  itself,  as  in  the 
contrivance  of  Professor  Daniell ;  in  this  way  all  danger  is 
avoided.  The  eye  speedily  becomes  accustomed  to  the  pecu- 
liar appearance  of  the  true  hydro-oxygen  flame,  so  as  to 
permit  the  supply  of  each  gas  to  be  exactly  regulated  by 
suitable  stop-cocks  attached  to  the  jet  (fig.  84). 

A  piece  of  thick  platinum  wire  introduced  into  the  flame 
of  the  hydro-oxygen  blowpipe  melts  with  the  greatest  ease ; 
a  watch-spring  or  small  steel  file  burns  with  the  utmost 
brilliancy,  throwing  off  showers  of  beautiful  sparks  ;  an  in- 

*  Professor  Graham  has  since  published  a  very  exten;?ive  series  of  researches  on  the  pas- 
Bage  of  jrases  through  narrow  tubes,  which  will  be  found  in  detail  in  the  Pbilosonhi'^al  Tran* 
actions  for  1846,  p.  573. 

10* 


114  HYDROGEN. 

combustible  oxidized  body,  as  magnesia  or  lime,  becomes  so  intensely  ig- 
nited, as  to  glow  with  a  light  insupportable  to  the  eye,  and  to  be  susceptible 
of  employment  as  a  most  powerful  illuminator,  as  a  substitute  for  the  sun's 
rays  in  the  solar  microscope,  and  for  night-signals  in  trigonometrical  surveys. 
If  a  long  glass  tube,  open  at  both  ends,  be  held  over  a  jet  of  hydro- 
Fig.  85,  gen  (fig_  85),  a  series  of  musical  sounds  are  sometimes  produced  by 
^j  the  partial  extinction  and  rekindling  of  the  flame  by  the  ascending 
'^  current  of  air.  These  little  explosions  succeed  each  other  at  regular 
intervals,  and  so  rapidly  as  to  give  rise  to  a  musical  note,  the  pitch 
depending  chiefly  upon  the  length  and  diameter  of  the  tube. 

Although  oxygen  and  hydrogen  may  be  kept  mixed  at  common 
temperatures  for  any  length  of  time  without  combination  taking 
place,  yet,  under  particular  circumstances,  they  unite  quietly  and 
without  explosion.  Some  years  ago.  Professor  Dobereiner,  of  Jena, 
made  the  curious  observation,  that  finely-divided  platinum  possessed 
the  power  of  determining  the  union  of  the  gases ;  and,  more  recently, 
Mr.  Faraday  has  shown  that  the  state  of  minute  division  is  by  no 
means  indispensable,  since  rolled  plates  of  the  metal  had  the  same 
property,  provided  their  surfaces  were  absolutely  clean.  Neither  is 
the  effect  strictly  confined  to  platinum ;  other  metals,  as  palladium 
and  gold,  and  even  stones  and  glass,  enjoy  the  same  property, 
although  to  a  far  inferior  degree,  since  they  often  require  to  be  aided 
by  a  little  heat.  When  a  piece  of  platinum  foil,  which  has  been 
cleaned  by  hot  oil  of  vitriol  and  thorough  washing  with  distilled 
water,  is  tjirust  into  a  jar  containing  a  mixture  of  oxygen  and  hydro- 
gen standing  over  water,  combination  of  the  two  gases  immediately 
begins,  and  the  level  of  the  water  rapidly  rises,  the  platinum 
becoming  so  hot,  that  drops  of  water  accidentally  falling  upon  it 
enter  into  ebullition.  If  the  metal  be  very  thin  and  exceedingly  clean,  and 
the  gases  very  pure,  then  its  temperature  rises  after  a  time  to  actual  redness, 
and  the  residue  of  the  mixture  explodes.  But  this  is  an  efi"ect  altogether 
accidental,  and  dependent  upon  the  high  temperature  of  the  platinum,  which 
high  temperature  has  been  produced  by  the  preceding  quiet  combination  of 
the  two  bodies.  When  the  platinum  is  reduced  to  a  state  of  division,  and 
its  surface  thereby  much  extended,  it  becomes  immediately  red-hot  in  a 
mixture  of  hydrogen  and  oxygen,  or  hydrogen  and  air;  a  jet  of  hydrogen 
thrown  upon  a  little  of  the  spongy  metal,  contained  in  a  glass  or  capsule, 
becomes  at  once  kindled,  and  on  this  principle  machines  for  the  production 
of  instantaneous  light  have  been  constructed.  These,  however,  only  act 
well  when  constantly  used  ;  the  spongy  platinum  is  apt  to  become  damp  by 
absorption  of  moisture  from  the  air,  and  its  power  is  then  for  the  time  lost. 
The  best  explanation  that  can  be  given  of  these  curious  eff"ects,  is  to  sup- 
pose that  solid  bodies  in  general  have,  to  a  greater  or  less  extent,  the  pro- 
perty of  condensing  gases  upon  their  surfaces,  and  that  this  faculty  is 
enjoyed  pre-eminently  by  certain  of  the  non-oxidizable  metals,  as  platinum 
and  gold.  Oxygen  and  hydrogen  may  thus,  under  these  circumstances,  be 
brought,  as  it  were,  within  the  sphere  of  their  mutual  attractions  by  a  tem- 
porary increase  of  density,  whereupon  combination  ensues. 

Coal-gas  and  ether  or  alcohol  vapour  may  be  made  to  exhibit  the  phenome- 
non of  quiet  oxidation  under  the  influence  of  this  remarkable  surface-action. 
A  close  spiral  of  slender  platinum  wire,  a  roll  of  thin  foil,  or  even  a  common 
platinum  crucible,  heated  to  dull  redness,  and  then  held  in  a  jet  of  coal-gas, 
becomes  strongly  ignited,  and  remains  in  that  state  as  long  as  the  supply  of 
mixed  gas  and  air  is  kept  up,  the  temperature  being  maintained  by  the  heat 
disengaged  in  the  act  of  union.  Sometimes  the  metal  becomes  white-hot, 
and  then  the  gas  takes  fire. 


HYDROGEN.  115 

A  very  pleasing  experiment  may  be  made  by  attaching  such  a  coil  ot  -wire 
to  a  card,  and  suspending  it  in  a  glass  containing  a  few  drops  of  ether 
(fig.  86),  having  previously  made  it  red-hot  in  the  flame 
of  a  spirit-lamp.     The  wire  continues  to  glow  until  the  Fig.  86. 

oxygen  of  the  air  is  exhausted,  giving  rise  to  the  pro- 
duction of  an  irritating  vapour  which  attacks  the  eyes. 
The  combustion  of  the  ether  is  in  this  case  but  partial ; 
a  portion  of  its  hydrogen  is  alone  removed,  and  the 
whole  of  the  carbon  left  untouched. 

A  coil  of  thin  platinum  wire  may  be  placed  over  the 
wick  of  a  spirit-lamp,  or  a  ball  of  spongy  platinum  sus- 
tained just  above  the  cotton  ;  on  lighting  the  lamp,  and 
then  blowing  it  out  as  soon  as  the  metal  appears  red-hot, 
slow  combustion  of  the  spirit  drawn  up  by  the  capillarity 
of  the  wick  will  take  place,  accompanied  by  the  pungent  ^"^"CT^ 

vapours  just   mentioned,  which  may  be  modified,  and  C;J~Z^ 

even  rendered  agreeable,  by  dissolving  in  the  liquid  some  "^ 

sweet-smelling  essential  oil  or  resin. 

Hydrogen  forms  numerous  compounds  with  other  bodies,  although  it  is 
greatly  surpassed  in  this  respect  not  only  by  oxygen,  but  by  many  of  the 
other  elements.  The  chemical  relations  of  hydrogen  tend  to  place  it  beside 
the  metals.  The  great  discrepancy  in  physical  properties  is  perhaps  more 
apparent  than  real.  Hydrogen  is  yet  unknown  in  the  solid  condition,  while, 
on  the  other  hand,  the  vapour  of  the  metal  mercury  is  as  transparent  and 
colourless  as  hydrogen  itself.  This  vapour  is  only  about  seven  times  heavier 
than  atmospheric  air,  so  that  the  difference  in  this  respect  is  not  nearly  so 
great  as  that  in  the  other  direction  between  air  and  hydrogen. 

There  are  two  oxides  of  hydrogen,  namely,  water,  and  a  very  peculiar 
substance,  discovered  in  the  year  1818,  by  M.  Thenard,  called  binoxide  of 
hydrogen. 

It  appears  that  the  composition  of  water  was  first  demonstrated  in  the 
year  1781,  by  Mr.  Cavendish,'  but  the  discovery  of  the  exact  proportions  in 
which  oxygen  and  hydrogen  unite  in  generating  that  most  important  com- 
pound has  from  time  to  time  to  the  present  day  occupied  the  attention  of 
some  of  the  most  distinguished  cultivators  of  chemical  science.  There  are 
two  distinct  methods  of  research  in  chemistry :  the  analytical,  or  that  in  which 
the  compound  is  resolved  into  its  elements,  and  the  synthetical,  in  which  the 
elements  are  made  to  unite  and  produce  the  compound.  The  first  method 
is  of  much  more  general  application  than  the  second,  but  in  this  particular 
instance  both  may  be  employed,  although  the  results  of  the  synthesis  are 
most  valuable. 

The  most  elegant  example  of  analysis  of  water  would  probably  be  foun  I 
in  its  decomposition  by  voltaic  electricity.  When  water  is  acidulated  so  as 
to  render  it  a  conductor,  and  a  portion  interposed  between  a  pair  of  platinum 
plates  connected  with  the  extremities  of  a  voltaic  apparatus  of  moderate 
power,  decomposition  of  the  liquid  takes  place  in  a  very  interesting 
.manner ;  oxygen,  in  a  state  of  perfect  purity,  is  evolved  from  the  water  in 
contact  ^ith  the  plate  belonging  to  the  copper  end  of  the  battery,  and 
hydrogen,  equally  pure,  is  disengaged  at  the  plate  connected  with  the  zinc 
extremity,  the  middle  portions  of  liquid  remaining  apparently  unaltered 
By  placing  small  graduated  jars  over  the  platinum  plates,  the  gases  can  be 

*  A  claim  to  the  discovery  of  the  composition  of  water  on  behalf  of  Mr.  James  Watt,  han 
been  very  strongly  urged,  and  supported  by  such  evidence  that  the  reader  of  the  controversy 
may  be  led  to  the  conclusion  that  the  discovery  was  made  by  both  parties  nearly  limulta- 
ne  lusly,  and  unknown  to  each  other.  ^ 


T16 


HYDROGEN. 


Fig.  87. 


Fig.  88. 


collected,  and  their  quantities  determined. 
Fig.  87  will  show  at  a  glance  the  whole 
arrangement;  the  conducting  wires  pass 
through  the  bottom  of  the  glass  cup,  and 
thence  to  the  battery. 

When  this  experiment  has  been  con- 
tinued a  sufficient  time,  it  will  be  found 
that  the  volume  of  the  hydrogen  is  a  very 
little  above  twice  that  of  the  oxygen ; 
were  it  not  for  the  accidental  circumstance 
of  oxygen  being  sensibly  more  soluble  in 
water  than  hydrogen,  the  proportion  of 
two  to  one  by  measure  would  come  out 
exactly. 

Water,  as  Mr.  Grove  has  lately  shown, 
is  likewise  decomposed  into  its  constituents 
by  heat.  The  effect  is  produced  by  intro- 
ducing platinum  balls,  ignited  by  electricity  or  other  means, 
Into  water  or  steam.  The  two  gases  are,  however,  obtained 
in  very  small  quantities  at  a  time. 

When  oxygen  and  hydrogen,  both  as  pure  as  possible,  are 
mixed  in  the  proportions  mentioned,  passed  into  a  strong  glass 
tube  filled  with  mercury,  and  exploded  by  the  electric  spark, 
all  the  mixture  disappears,  and  the  mercury  is  forced  up  into 
the  tube,  filling  it  completely.  The  same  experiment  may  be 
made  with  the  explosion-vessel  or  eudiometer  of  Mr.  Caven- 
dish. (Fig.  88.)  The  instrument  is  exhausted  at  the  air- 
pump,  and  then  filled  from  a  capped  jar  with  the  mixed 
gases ;  on  passing  an  electric  spark  by  the  wires  shown  at  a, 
explosion  ensues,  and  the  glass  becomes  bedewed  with 
moisture,  and  if  the  stop-cock  be  then  opened  under  water, 
the  latter  will  rush  in  and  fill  the  vessel,  leaving  merely  a 
bubble  of  air,  the  result  of  an  imperfect  exhaustion. 

The  process  upon  which  most  reliance  is  placed  is  that  in 
which  pure  oxide  of  copper  is  reduced  at  a  red  heat  by  hy- 
drogen, and  the  water  so  formed  collected  and  weighed.    This 
oxide  suffers  no  cliange  by  heat  alone,  but  the  momentary 
contact  of  hydrogen,  or  any  common  combustible  matter  at  a  high  tem- 
perature, suffices  to  reduce  a  corresponding  portion  to  the  metallic  state 
Fig.  89  will  serve  to  convey  some  idea  of  the  arrangement  adopted  in  re 
searches  of  this  kind. 

Fig.  89. 


A  copious  supply  of  hydrogen  is  procured  by  the  action  of  dilute  sul- 
phuric acid  upon  the  purest  zinc  that  can  be  obtained  ;  the  gas  is  made  to 
pass  in  succession  through  solutions  of  silver  and  strong  caustic  potassa,  by 
vb'ch  its  purification  is  completed.     After  this,  it  is  conducted  through  a 


HYDROGEN.  11 7 

tube  three  or  four  feet  in  length,  filled  with  fragments  of  pumice-stone 
steeped  in  concentrated  oil  of  vitriol,  or  with  anhydrous  phosphoric  acid. 
These  substances  have  such  an  extraordinary  attraction  for  aqueous  vapour, 
that  they  dry  the  gas  completely  during  its  transit.  The  extremity  of  this 
tube  is  shown  at  a.  The  dry  hydrogen  thus  arrives  at  the  part  of  the  appa- 
ratus containing  the  oxide  of  copper,  represented  at  b ;  this  consists  of  a 
two-necked  flask  of  very  hard  white  glass,  maintained  at  a  red  heat  by  a 
spirit-lamp  placed  beneath.  As  the  decomposition  proceeds,  the  water  pro- 
duced by  the  reduction  of  the  oxide  begins  to  condense  in  the  second  neck 
of  the  flask,  whence  it  drops  into  the  receiver  c,  provided  for  the  purpose. 
A  second  desiccating  tube  prevents  the  loss  of  aqueous  vapour  by  the  cur- 
rent of  gas  which  passes  in  excess. 

Before  the  experiment  can  be  commenced,  the  oxide  of  copper,  the  purity 
of  which  is  well  ascertained,  must  be  heated  to  redness  for  some  time  in  a 
current  of  dry  air ;  it  is  then  suffered  to  cool,  and  very  carefully  weighed 
with  the  flask.  The  empty  receiver  and  second  drying  tube  are  also  weighed, 
the  disengagement  of  gas  set  up,  and  when  the  air  has  been  displaced,  heat 
slowly  applied  to  the  oxide.  The  action  is  at  first  very  energetic ;  the  oxide 
often  exhibits  the  appearance  of  ignition ;  as  the  decomposition  proceeds,  it 
becomes  more  sluggish,  and  requires  the  application  of  a  good  deal  of  heat 
to  eff'ect  its  completion. 

When  the  process  is  at  an  end,  and  the  apparatus  perfectly  cool,  the 
stream  of  gas  is  discontinued,  dry  air  is  drawn  through  the  whole  arrange- 
ment, and,  lastly,  the  parts  are  disconnected  and  re-weighed.  The  loss  of 
the  oxide  of  copper  gives  the  oxygen ;  the  gain  of  the  receivei  and  its  dry- 
ing-tube indicates  the  water,  and  the  difference  between  the  two,  the  hy- 
drogen. 

A  set  of  experiments,  made  in  Paris  in  the  year  1820,*  by  MM.  Dulong 
and  Berzelius,  gave  as  a  mean  result  for  the  composition  of  water  by  weight, 
8-009  parts  oxygen  to  1  part  hydrogen ;  numbers  so  nearly  in  the  proportion 
of  8  to  1,  that  the  latter  have  usually  been  assumed  to  be  true. 

Quite  recently  the  subject  has  been  re-investigated  by  M.  Dumas,'^  with 
the  most  scrupulous  precision,  and  the  above  supposition  fully  confirmed. 
The  composition  of  water  may  therefore  be  considered  as  established:  it 
contains  by  weight  8  parts  oxygen  to  1  part  hydrogen,  and  by  measure,  1 
volume  oxygen  to  2  volumes  hydrogen.  The  densities  of  the  gases,  as  al- 
ready mentioned,  correspond  very  closely  with  these  results. 

The  physical  properties  of  water  are  too  well  known  to  need  lengthened 
description ;  it  is,  when  pure,  colourless  and  transparent,  destitute  of  taste 
and  odour,  and  an  exceedingly  bad  conductor  of  electricity  of  low  tension. 
It  attains  its  greatest  density  towards  40°  (4o-5C),  freezes  at  32°  {0°G),  and 
boils  under  the  pressure  of  the  atmosphere  at  or  near  212°  (100°C).  It 
evaporates  at  all  temperatures.  One  cubic  inch  at  62°  (16°-7C)  weighs 
252-45  grains.  It  is  815  times  heavier  than  air;  an  imperial  gallon  weighs 
70,000  grains  or  10  lb.  avoirdupois.  To  all  ordinary  observation,  water  is 
incompressible ;  very  accurate  experiments  have  nevertheless  shown  that  it 
does  yield  to  a  small  extent  when  the  power  employed  is  very  great ;  the 
diminution  of  volume  for  each  atmosphere  of  pressure  being  about  51-mil- 
lionths  of  the  whole. 

Clear  water,  although  colourless  in  small  bulk,  is  blue  like  the  atmosphere 
when  viewed  in  mass.  This  is  seen  in  the  deep  ultramarine  tint  of  the  ocean, 
and  perhaps  in  a  still  more  beautiful  manner  in  the  lakes  of  Switzerland 
and  other  Alpine  countries,  and  in  the  rivers  which  issue  from  them ;.  the 
slightest  admixture  of  mud  or  suspended  impurity  destroying  the  effect. 

»  Ann.  Chim.  et  Phys.  xv.  386.  «  Ann.  Chim.  et  Phys.  3rd  series,  viii.  189i 


118  HYDROGEN. 

The  same  maguificent  colour  is  visible  in  the  fissures  and  caverns  found  in 
the  ice  of  the  glaciers,  which  is  usually  extremely  pure  and  transparent 
within,  although  foul  upon  the  surface. 

Steam,  or  vapour  of  water,  in  its  state  of  greatest  density  at  212°  (100°C), 
compared  with  air  at  the  same  temperature,  and  possessing  an  equal  elastic 
force,  has  a  specific  gravity  expressed  by  the  fraction  of  0-625.  In  this  con- 
dition, it  may  be  represented  as  containing,  in  every  two  volumes,  two 
volumes  of  hydrogen,  and  one  volume  of  oxygen. 

Water  seldom  or  never  occurs  in  nature  in  a  state  of  perfect  purity ;  even 
the  rain  which  falls  in  the  open  country,  contains  a  trace  of  ammoniacal  salt, 
while  rivers  and  springs  are  invariably  contaminated  to  a  greater  or  less 
extent  with  soluble  matters,  saline  and  organic.  Simple  filtration  through  a 
porous  stone  or  a  bed  of  sand  will  separate  suspended  impurities,  but  dis- 
tillation alone  will  free  the  liquid  from  those  that  are  dissolved.  In  the  pre- 
paration of  distilled  water,  which  is  an  article  of  large  consumption  in  the 
scientific  laboratory,  it  is  proper  to  reject  the  first  portions  which  pass  over, 
and  to  avoid  carrying  the  distillation  to  dryness.  The  process  may  be  con- 
ducted in  a  metal  still  furnished  with  a  worm  or  condenser  of  silver  or  tin ; 
lead  must  not  be  used. 

The  ocean  is  the  great  recipient  of  the  saline  matter  carried  down  by  the 
rivers  which  drain  the  land ;  hence  the  vast  accumulation  of  salts.  The 
following  table  will  serve  to  convey  an  idea  of  the  ordinary  composition  of 
sea-water ;  the  analysis  is  by  Dr.  Schweitzer,'  of  Brighton,  the  water  being 
that  of  the  Channel : — 

1000  grains  contained 

Water 964-745 

Chloride  of  sodium 27-059 

Chloride  of  potassium 0-766            ' 

Chloride  of  magnesium 3-666 

Bromide  of  magnesium 0-029 

Sulphate  of  magnesia 2-296 

Sulphate  of  lime 1-406 

Carbonate  of  lime 0-033 

Traces  of  iodine  and  ammoniacal  salt 

1000-000 

Its  specific  gravity  was  found  to  be  1-0274  at  60°  (15°-5C). 

Sea- water  is  liable  to  variations  of  density  and  composition  by  the  influence 
of  local  causes,  such  as  the  proximity  of  large  rivers  or  masses  of  melting 
ice,  and  other  circumstances. 

Natural  springs  are  often  impregnated  to  a  great  extent  with  soluble  sub- 
stances derived  from  the  rocks  they  traverse ;  such  are  the  various  mineral 
waters  scattered  over  the  whole  earth,  and  to  which  medicinal  virtues  are 
attributed.  Some  of  these  hold  protoxide  of  iron  in  solution,  and  are  efi^er- 
vescent  from  carbonic  acid  gas ;  others  are  alkaline,  probably  from  traver- 
sing rocks  of  volcanic  origin ;  some  contain  a  very  notable  quantity  of  iodine 
or  bromine.  Their  temperatures  also  are  as  variable  as  their  chemical 
nature.  A  tabular  notice  of  some  of  the  most  remarkable  of  these  waters 
will  be  found  in  the  Appendix. 

Water  enters  into  direct  combination  with  other  bodies,  forming  a  class 
of  compounds  called  hydrates ;  the  action  is  often  very  energetic,  much  heat 
being  evolved,  as  in  the  case  of  the  slaking  of  lime,  which  is  really  the  pro- 
duction of  a  hydrate  of  that  base.     Sometimes  the  attraction  between  the 

»  Phil.  Mag.  July,  1839. 


HYDROGEN.  119 

water  and  the  second  body  is  so  great  that  the  compound  is  not  decomposable 
by  any  heat  that  can  be  applied ;  the  hydrates  of  potassa  and  soda,  and  of 
phosphoric  acid,  furnish  examples.  Oil  of  vitriol  is  a  hydrate  of  sulphuric 
acid,  from  which  the  water  cannot  be  thus  separated. 

Water  very  frequently  combines  with  saline  substances  in  a  less  intimate 
manner  than  that  above  described,  constituting  what  is  called  water  of  crys- 
tallization, from  its  connexion  with  the  geometrical  figure  of  the  salt.  In 
this  case  it  is  easily  driven  off  by  the  application  of  heat. 

Lastly,  the  solvent  properties  of  water  far  exceed  those  of  any  other  liquid 
known.  Among  salts,  a  very  large  proportion  are  soluble  to  a  greater  or 
less  extent,  the  solubility  usually  increasing  with  the  temperature,  so  that  a 
hot  saturated  solution  deposits  crystals  on  cooling.  There  are  a  few  excep- 
tions to  this  law,  one  of  the  most  remarkable  of  which  is  common  salt,  the 
solubility  of  which  is  nearly  the  same  at  all  temperatures ;  the  hydrate  and 
certain  organic  salts  of  lime,  also,  dissolve  more  freely  in  cold  than  in  hot 
water. 

Water  dissolves  gases,  but  in  very  unequal  quantities ;  some,  as  hydrogen, 
oxygen,  and  atmospheric  air,  are  but  little  acted  upon ;  others,  as  ammonia 
and  hydrochloric  acid,  are  absorbed  to  an  enormous  extent ;  and  between 
these  extremes  there  are  various  intermediate  degrees.  Generally,  the  colder 
the  water,  the  more  gas  does  it  dissolve ;  a  boiling  heat  disengages  the  whole, 
if  the  gas  be  not  very  soluble. 

When  water  is  heated  in  a  strong  vessel  to  a  temperature  above  that  of 
the  ordinary  boiling-point,  its  solvent  powers  are  still  further  increased. 
Dr.  Turner  inclosed  in  the  upper  part  of  a  high-pressure  steam-boiler,  worked 
at  300°  {149°C),  pieces  of  plate  and  crown  glass.  At  the  expiration  of  four 
months  the  glass  was  found  completely  corroded  by  the  action  of  the  water ; 
what  remained  was  a  white  mass  of  silica,  destitute  of  alkali,  while  stalac- 
tites of  siliceous  matter,  above  an  inch  in  length,  depended  from  the  little 
wire  cage  which  inclosed  the  glass.  This  experiment  tends  to  illustrate  the 
changes  which  may  be  produced  by  the  action  of  water  at  a  high  tempe- 
rature in  the  interior  of  the  earth  upon  felspathic  and  other  rocks.  Some- 
thing of  the  sort  is  manifest  in  the  Geyser  springs  of  Iceland,  which  deposit 
siliceous  sinter.* 

Binozide  of  hydrogen,  sometimes  called  oxygenated  icaier,  is  an  exceedingly 
interesting  substance,  but  unfortunatiely  very  difficult  of  preparation.  It  is 
formed  by  dissolving  the  binoxide  of  barium  in  dilate  hydrochloric  acid, 
carefully  cooled  by  ice,  and  then  precipitating  the  baryta  by  sulphuric  acid  ; 
the  excess  of  oxygen  of  the  binoxide,  instead  of  being  disengaged  as  gas, 
unites  with  a  portion  of  the  water,  and  converts  it  into  binoxide  of  hydrogen. 
This  treatment  is  repeated  with  the  same  solution  and  fresh  portions  of  the 
binoxide  of  barium  until  a  considerable  quantity  of  the  latter  has  been  con- 
sumed, and  a  corresponding  amount  of  binoxide  of  hydrogen  formed.  The 
liquid  yet  contains  hydrochloric  acid,  to  get  rid  of  which  it  is  treated  in  suc- 
cession with  sulphate  of  silver  and  baryta-water.  The  whole  process  re- 
quires the  utmost  care  and  attention.  The  binoxide  of  barium  itself  is  pre- 
pared by  exposing  pure  baryta,  contained  in  a  red-hot  porcelain  tube,  to  a 
stream  of  oxygen.  The  solution  of  binoxide  of  hydrogen  may  be  concep- 
trated  under  the  air-pump  receiver  until  it  acquires  the  specific  gravity  of 
1'45.  In  this  state  it  presents  the  aspect  of  a  colourless,  transparent,  ino- 
dorous liquid,  possessing  remarkable  bleaching  powers.  It  is  very  prone  to 
decomposition  ;  the  least  elevation  of  temperature  causes  efi^ervescence,  due 
to  the  escape  of  oxygen  gas ;  near  212°  (100°C)  it  is  decomposed  with  ex. 

»  Phil.  Mag.  Oct.  1834. 


120  NITROGEN. 

plosive  violence.     Binoxide  of  hydrogen   contains   exactly  twice  as  much 
>xygen  as  water,  or  16  parts  to  1  part  of  hydrogen. 

NITROGEN. 

Nitrogen'  constitutes  about  four-fifths  of  the  atmosphere,  and  enters  Into 
a  great  variety  of  combinations.  It  may  be  prepared  for  the  purpose  of  expe- 
riment by  several  methods.  One  of  the  simplest  of  these  is  to  burn  out  the 
oxygen  from  a  confined  portion  of  air,  by  phosphorus,  or  by  a  jet  of  hy- 
drogen. 

A  small  porcelain  capsule  is  floated  on  the  water  of  the  pneumatic  trough, 
and  a  piece  of  phosphorus  placed  in  it  and  set  on  fire. 
Fig-  90.  (Fig.  90.)     A  bell-jar  is  then  inverted  over  the  whole, 

and  suffered  to  rest  on  the  shelf  of  the  trough,  so  as 
to  project  a  little  over  its  edge.  At  first,  the  heat 
causes  expansion  of  the  air  of  the  jar,  and  a  few  bub- 
bles are  expelled,  after  which  the  level  of  the  water 
rises  considerably.  When  the  phosphorus  becomes 
extinguished  by  exhaustion  of  the  oxygen,  and  time 
has  been  given  for  the  subsidence  of  the  cloud  of  finely- 
divided,  snow-like  phosphoric  acid,  which  floats  in  the 
residual  gas,  the  nitrogen  may  be  decanted  into  ano- 
ther vessel,  and  its  properties  examined. 

Prepared  by  the  foregoing  process,  nitrogen  is  con- 
taminated by  a  little  vapour  of  phosphorus,  which 
communicates  its  peculiar  odour.  A  preferable  me- 
thod is  to  fill  a  porcelain  tube  with  turnings  of  copper, 
or,  still  better,  with  the  spongy  metal  obtained  by  reducing  the  oxide  by 
hydrogen ;  to  heat  this  tube  to  redness,  and  then  pass  through  it  a  stream 
of  atmospheric  air,  the  oxygen  of  which  is  entirely  removed  during  its  pro- 
gress by  the  heated  copper. 

If  chlorine  gas  be  passed  into  solution  of  ammonia,  the  latter  substance, 
which  is  a  compound  of  nitrogen  with  hydrogen,  is  decomposed ;  the  chlo- 
rine combines  with  the  hydrogen,  and  the  nitrogen  is  set  free  with  efferves- 
cence. In  this  manner  very  pure  nitrogen  can  be  obtained.  In  making  this 
experiment,  it  is  necessary  to  stop  short  of  saturating  or  decomposing  the 
whole  of  the  ammonia,  otherwise  there  will  be  great  risk  of  accident  from 
the  formation  of  an  exceedingly  dangerous  explosive  compound  formed  by 
the  contact  of  chlorine  with  an  ammoniacal  salt. 

Nitrogen  is  destitute  of  colour,  taste,  and  smell ;  it  is  a  little  lighter  than 
air,  its  density  being,  according  to  Dumas,  0-972.  100  cubic  inches,  at  60° 
(15°-6C),  and  30  inches  barometer,  will  therefore  weigh  30-14  grains.  Nitro- 
gen is  incapable  of  sustaining  combustion  or  animal  existence,  although,  like 
hydrogen,  it  has  no  positive  poisonous  properties ;  neither  is  it  soluble  to 
any  notable  extent  in  water  or  in  caustic  alkali ;  it  is,  in  fact,  best  charac- 
terized by  negative  properties. 

The  exact  composition  of  the  atmosphere  has  repeatedly  been  made  the 
mbject  of  experimental  research.  Besides  nitrogen  and  oxygen,  the  air 
itontains  a  little  carbonic  acid,  a  very  variable  proportion  of  aqueous  vapour, 
R  trace  of  ammonia,  and,  perhaps,  a  little  carburetted  hydrogen.  The  oxygen 
and  nitrogen  are  in  a  state  of  mixture,  not  of  combination,  yet  their  ratio 
is  always  uniform.  Air  has  been  brought  from  lofty  Alpine  heights,  and 
compared  with  that  from  the  plains  of  Egypt ;  it  has  been  brought  from  an 
elevation  of  21,000  feet  by  the  aid  of  a  balloon ;  it  has  been  collected  and 
examined  in  London  and  Paris,  and  many  other  districts ;  still  the  propor- 

*  i.  e.  Generator  of  nitre ;  also  called  azote,  from  a,  privative,  and  ^w^,  life. 


NITROGEN. 


121 


tions  of  oxygen  and  nitrogen  remain  unaltered,  the  diflFusive  energy  of  the 
gases  being  adequate  to  maintain  this  perfect  uniformity  of  mixture.  The 
carbonic  acid,  on  the  contrary,  being  much  influenced  by  local  causes,  varies 
considerably.  In  the  following  table  the  proportion  of  oxygen  and  nitrogen 
are  given  on  the  authority  of  M.  Dumas,  and  the  carbonic  acid  on  that  of 
De  Saussure ;  the  ammonia,  the  discovery  of  which  is  due  to  Liebig,  is  too 
small  in  quantity  for  direct  estimation. 


Composition  of  the  Atmospfiere. 
By  weight. 

Nitrogen 77  parts  

Oxygen  23     "       


By  measure. 
..  79-19 
..  20-81 


Tig.  91. 


100  100-00 

Carbonic  acid,  from  3-7  measures  to  6-2  measures,  in  10,000  measures  of 
air. 

Aqueous  vapour  variable,  depending  much  upon  the  temperature. 

Ammonia,  a  trace.  ^ 

100  cubic  inches  of  pure  and  dry  air  weigh,  according  to  Br.  Front, 
31-0117  grains;  the  temperature  being  60°  F.  (15°-5C)  and  the  baro- 
meter standing  at  30  inches. 

The  analysis  of  air  is  very  well  effected  by  passing  it 
over  finely-divided  copper  contained  in  a  tube  of  hard  glass, 
3aref\illy  weighed,  and  then  heated  to  redness ;  the  ni- 
trogen is  suffered  to  flow  into  an  exhausted  glass  globe, 
also  previously  weighed.  The  increase  of  weight  after 
the  experiment  gives  the  information  sought. 

An  easier,  but  less  accurate  method,  consists  in  intro- 
ducing into  a  graduated  tube,  standing  over  water  (fig.  91), 
i  known  quantity  of  the  air  to  be  examined,  and  then 
passing  into  the  latter  a  stick  of  phosphorus  aflSxed  to 
the  end  of  a  wire.  The  whole  is  left  about  twenty-four 
hours,  during  which  the  oxygen  is  slowly  but  completely 
absorbed,  after  which  the  phosphorus  is  withdrawn  and  the 
residual  gas  read  off. 

Professor  Liebig  has  lately  proposed  to  use  an  alkaline 
solution  of  pyro-gallic  acid,  (a  substance  which  will  be 
described  in  the  department  of  organic  chemistry,)  for  the 
absorption  of  oxygen.  The  absorptive  power  of  such  a 
solution,  which  turns  deep  black  on  coming  in  contact  with 
the  oxygen,  is  very  considerable.  Liebig's  method  combines  great  accuracv 
with  unusual  rapidity  and  facility  of  execution. 

Another  plan  is  to  mix  the  air  with  hydrogen  and  pass  an  electric  sparK ; 
after  the  explosion  the  volume  of  gas  is  read  off  and  compared  with  that  of 
the  air  employed.  Since  the  analysis  of  gaseous  bodies  by  explosion  is  an 
operation  of  great  importance  in  practical  chemistry,  it  may  be  worth  while 
describing  the  process  in  detail,  as  it  is  applicable,  with  certain  obvious 
variations,  to  a  number  of  analogous  cases. 

A  convenient  form  of  apparatus  for  the  purpose  is  the  siphon  eudiometer 
of  Dr.  Ure ;  this  consists  of  a  stout  glass  tube,  having  an  internal  diameter 
»f  about  one-third  of  an  inch,  closed  at  one  end,  and  bent  into  the  form 
represented  in  the  drawing.  (Fig.  92.)  Two  pieces  of  platinum  wire, 
melted  into  the  glass  near  the  closed  extremity,  serve  to  give  passage  to  the 
spark.     The  closed  limb  is  carefully  graduated.    When  required  for  use,  th* 


tS2 


NITROGEN. 


Fig.  92. 


instrument  is  filled  with  mercury  and  inverted  into  a 
vessel  of  the  same  fluid.  A  quantity  of  the  air  to  be 
examined  is  then  introduced,  the  manipulation  being 
precisely  the  same  as  with  experiments  over  water ; 
the  open  end  is  stopped  with  a  finger,  and  the  air 
transferred  to  the  closed  extremity.  The  instrument 
is  next  held  upright,  and  after  the  level  of  the  mer- 
cury has  been  made  equal  on  both  sides  by  displacing 
a  portion  from  the  open  limb  by  thrusting  down  a 
piece  of  stick,  the  volume  of  air  is  read  oflF.  This 
done,^the  open  part  of  the  tube  is  again  filled  up  with 
mercury,  closed  with  the  finger,  inverted  into  the 
liquid  metal,  and  a  quantity  of  pure  hydrogen  intro- 
duced, equal,  as  nearly  as  can  be  guessed,  to  about 
half  the  volume  of  the  air.  The  eudiometer  is  once 
more  brought  into  an  erect  position,  the  level  of  the 
mercury  equalized,  and  the  volume  again  read  oflF; 
the  quantity  of  hydrogen  added  is  thus  accurately 
ascertained.  All  is  now  ready  for  the  explosion  ;  the 
instrument  is  held  in  the  way  represented,  the  open 
end  being  firmly  closed  by  the  thumb,  while  the  knuckle  of  the  fore-finger 
touches  the  nearer  platinum  wire ;  the  spark  is  then  passed  by  the  aid  of  a 
charged  jar  or  a  good  electrophorus,  and  explosion  ensues.  The  air  con- 
fined by  the  thumb  in  the  open  part  of  the  tube  acts  as  a  spring  and  mode- 
rates the  explosive  efi'ect.  Nothing  now  remains  but  to  equalize  the  level 
of  the  mercury  by  pouring  a  little  more  into  the  instrument,  and  then  to 
read  off  the  volume  for  the  last  time. 

What  is  required  to  be  known  from  this  experiment  is  the  diminution  the 
mixture  suffers  by  explosion ;  for  since  the  hydrogen  is  in  excess,  and  since 
that  substance  unites  with  oxygen  in  the  proportion  by  measure  of  two  to 
one,  one-third  part  of  that  diminution  must  be  due  to  the  oxygen  contained 
in  the  air  introduced.  As  the  amount  of  the  latter  is  known,  the  proportion 
of  oxygen  it  contains  thus  admits  of  determination.  The  case  supposed 
will  render  this  clear. 

Air  introduced  100  measures 

Air  and  hydrogen 150 

Volume  after  explosion 87 

Diminution  63 

CO 

—  s  21 ;  oxygen  in  the  hundred  measures. 
3 

The  working  pupil  will  do  well  to  acquire  dexterity  in  the  use  of  this  val- 
uable instrument,  by  practising  the  transference  of  gas  or  liquid  from  the 
one  limb  to  the  other,  &c.  In  the  analysis  of  combustible  gases  by  explo- 
Bion  with  oxygen,  solution  of  caustic  potassa  is  often  required  to  be  intro- 
duced into  the  closed  part. 


Compounds  of  Nitrogen  and  Oxygen. 

There  are  not  less  than  five  distinct  compounds  of  nitrogen  and  oxygen, 
thus  named  and  constituted :  — 


NITROGEN 


123 


Composition  by  weight 


Nitrogen.  Oxygen. 

Protoxide  of  nitrogen* 14  8''^  ^ 

Binoxide  of  nitrogen'  14  16--N0«- 

Nitrous  acid 14  24-^/03 

Hvponitric  acid' 14  82  •=  W  O y 

Nitric  acid 14  40r. '^{OiT 

Nitric  or  Azotic  Acid. — It.  certain  parts  of  India,  and  also  in  other  hot  dry 
climates  where  rain  is  rare,  the  surface  of  the  soil  is  occasionally  covered 
by  a  saline  efflorescence,  like  that  sometimes  apparent  on  newly-plastered 
walls ;  this  substance  collected,  dissolved  in  hot  water,  the  solution  filtered  ' 
and  made  to  crystallize,  furnishes  the  highly  important  salt  known  in  com- 
merce as  nitre  or  saltpetre ;  it  js  a  compound  of  nitric  acid  and  potassa. 
To  obtain  liquid  nitric  acid,  equal  weights  of  powdered  nitre  and  oil  of 
vitriol  are  introduced  into  a  glass  retort,  and  heat  applied  by  means  of  an 
Argand  gas-lamp  or  charcoal  chauffer.  A  flask,  cooled  by  a  wet  cloth,  is 
adapted  to  the  retort,  to  serve  for  a  receiver.  No  luting  of  any  kind  must 
be  used. 

As  the  distillation  advances,  the  red  fumes  which  first  arise  disappear,  but 
towards  the  end  of  the  process  again  become  manifest.  When  this  happens, 
and  very  little  liquid  passes  over,  while  the  greater  part  of  the  saline  matter 
of  the  retort  is  in  a  state  of  tranquil  fusion,  the  operation  may  be  stopped ; 
and  when  the  retort  is  quite  cold,  water  may  be  introduced  to  dissolve  out 
the  bisulphate  of  potassa.     The  reaction  is  thus  explained. 


Nitre 


Nitric  acid 
Potassa 


Oil  of  vitriol  {g^yj[^^.^^^.^ 


Liquid  nitric  acid. 


Bisulphate  of  potassa. 


In  the  manufacture  of  nitric  acid  on  the  large  scale,  the  glass  retort  is 
replaced  by  a  cast-iron  cylinder,  and  the  receiver  by  a  series  of  earthen  con- 
densing vessels  connected  by  tubes.  (Fig.  93.)  Nitrate  of  soda,  found  native 
n  Peru,  is  often  substituted  for  nitrate  of  potassa. 

Fig.  93. 


Liquid  nitric  acid  so  obtained  has  a  specific  gravity  of  1-5  to  1-52 ;  it  has  a 
^>lden  yellow  colour,  which  is  due  to  nitrous  or  hyponitric  acid  held  in  solu- 
tion, and  which,  when  the  acid  is  diluted  with  water,  gives  rise  by  its  decom- 
position to  a  disengagement  of  nitric  oxide.  It  is  exceedingly  corrosive, 
staining  the  skin  deep  yellow,  and  causing  total  disorganization.  Poured 
upon  red-hot  powdered  charcoal,  it  causes  brilliant  combustion ;  and  when 
added  to  warm  oil  of  turpentine,  acts  upon  that  substance  so  energetically 
as  to  set  it  on  fire. 


«  Otherwise  called  nitrous  oxide.  ,    '/  1 

»  Called  by  Professor  Graham  peroxide  of  nitrogen. 


•  Otherwise  called  nitric  oxide, 


O-v 


124  NITROGEN. 

Pure  liquid  nitric  acid,  in  its  most  concentrated  form,  is  obtained  by  mix 
ing  the  above  with  about  an  equal  quantity  of  oil  of  vitriol,  re-distilling, 
collecting  apart  the  first  portion  which  comes  over,  and  exposing  it  in  a 
vessel  slightly  warmed,  and  sheltered  from  the  light,  to  a  current  of  dry 
air,  made  to  bubble  through  it,  which  completely  removes  the  nitrous  acid. 
In  this  state  the  product  is  as  colourless  as  water;  it  has  the  sp.  gr.  1-517 
at  60°  (15°-5C),  boils  at  184°  (84°-5C),  and  consists  of  54  parts  real  acid, 
and  9  parts  water.  Although  nitric  acid  in  a  more  dilute  form  acts  very 
violently  upon  many  metals,  and  upon  organic  substances  generally,  this  is 
not  the  case  with  the  compound  in  question ;  even  at  a  boiling  heat  it  re- 
fuses to  attack  iron  or  tin,  and  its  mode  of  action  on  lignin,  starch,  and 
similar  substances,  is  quite  peculiar,  and  very  much  less  energetic  than  that 
of  an  acid  containing  more  water. 

A  second  definite  compound  of  real  nitric  acid  and  water  exists,  containing 
54  parts  of  the  former  to  36  parts  of  the  latter.  Its  sp.  gr.  at  60°  (15° -50) 
is  1-424,  and  it  boils  at  250°  (121  °C).  An  acid  weaker  than  this  is  concen- 
trated to  this  point  by  evaporation ;  and  one  stronger,  reduced  to  the  same 
amount  by  loss  of  nitric  acid  and  water  in  the  form  of  the  first  hydrate.' 

Absolute  nitric  acid,  in  the  separate  state,  was  unknown  up  to  1849,  when 
M.  Deville  succeeded  in  obtaining  this  remarkable  substance  by  exposing 
nitrate  of  silver,  which  is  a  combination  of  nitric  acid,  silver,  and  oxygen, 
to  the  action  of  chlorine  gas.  Chlorine  and  silver  combine,  forming  chloride 
of  silver,  which  remains  in  the  apparatus,  whilst  oxygen  and  anhydrous 
nitric  acid  separate.  The  latter  is  a  colourless  substance,  crystallizing  in 
six-sided  columns,  which  fuse  at  86°  (30°C),  and  boil  between  113°  and 
122°  (45°  and  50°C),  when  they  commence  to  be  decomposed.  Anhydrous 
nitric  acid  has  been  found  to  explode  sometimes  spontaneously.  It  dissolves 
in  water  with  evolution  of  much  heat,  forming  hydrated  nitric  acid.  It  con- 
sists of  14  parts  of  nitrogen  and  40  parts  of  oxygen. 

Nitric  acid  forms  with  bases  a  very  extensive  and  important  group  of  salts, 
the  nitrates,  which  are  remarkable  for  all  being  soluble  in  water.  The 
hydrated  acid  is  of  great  use  in  the  laboratory,  and  also  in  many  branches 
of  industry. 

The  acid  prepared  in  the  way  described  is  apt  to  contain  traces  of  chlo- 
rine from  common  salt  in  the  niti-e,  and  sometimes  of  sulphate  from  acci- 
dental splashing  of  the  pasty  mass  in  the  retort.  To  discover  these  impuri- 
ties, a  portion  is  diluted  with  four  or  five  times  its  bulk  of  distilled  water, 
and  divided  between  two  glasses.  Solution  of  nitrate  of  silver  is  dropped 
into  the  one,  and  solution  of  nitrate  of  baryta  into  the  other ;  if  no  change 
ensue  in  either  case,  the  acid  is  free  from  the  impurities  mentioned. 

Nitric  acid  lias  been  formed  in  small  quantity  by  a  very  curious  process, 
namely,  by  passing  a  series  of  electric  sparks  through  a  portion  of  air, 
water,  or  an  alkaline  solution  being  present.  The  amount  of  acid  so  formed 
after  many  hours  is  very  minute ;  still  it  is  not  impossible  that  powerful 
discharges  of  atmospheric  electricity  may  sometimes  occasion  a  trifling  pro- 
duction of  nitric  acid  in  the  air.  A  very  minute  quantity  of  nitric  acid  is 
also  produced  by  the  combustion  of  hydrogen  and  other  substances  in  the 
atmosphere ;  it  is  also  formed  by  the  oxidation  of  ammonia. 

Nitric  acid  |s  not  so  easily  detected  in  solution  in  small  quantities  as  many 
other  acids.  Owing  to  tlie  solubility  of  all  its  compounds,  no  precipitant  can 
be  found  for  this  substance.  One  of  the  best  tests  is  its  power  of  bleaching 
a  solution  of  indigo  in  sulphtiric  acid  when  boiled  with  that  liquid.     The 

*  The  t-wo  hydrates  of  nitric  acid  are  thus  expressed  by  symbols : — NOe,  HO  and  NOe,  4H0. 
No  compound  containing  two  equivalents  of  water  appears  to  exist. 


NITROGEN. 


125 


absence  of  chlorine  must  be  ensured  in  this  experiment  by  means  which  will 

hereafter  be  obvious,  otherwise  the  result  is  equivocal. 

Protoxide  of  Nitrogen;  Nitrou*  Oxide;  (laughing  gas.) — When  solid  nitrate 
of  ammonia  is  heated  in  a  retort  or  flask,'  fig.  94,  furnished  with  a  perforated 
cork  and  bent  tube,  it  is  resolved  into  water  and  nitrous  oxide.  The  nature 
of  the  decomposition  will  be  understood  from  the  subjoined  diagram. 


.       ^         80 


I  Nitrogen  14 
Oxygen 
Oxygen 
Oxygen  24 
Nitrogen  14 
Hydrogen  3 
Water 


Protox.  nitrogen  22 


Protox.  nitrogen  22 
Water  27 


-Water  9. 


Fig.  94. 


No  particular  precaution  is  required  in  the  ope- 
ration, save  due  regulation  of  the  heat,  and  the 
avoidance  of  tumultuous  disengagement  of  the  gas. 

Protoxide  of  nitrogen  is  a  colourless,  transparent, 
and  almost  inodorous  gas,  of  distinctly  sweet  taste. 
Its  specific  gravity  is  1'525;  100  cubic  inches 
weigh  47-29  grains.  It  supports  the  combustion 
of  a  taper  or  piece  of  phosphorus  with  almost  as 
much  energy  as  pure  oxygen ;  it  is  easily  distin- 
guished, however,  from  that  gas  by  its  solubility  in 
cold  water,  which  dissolves  nearly  its  own  volume ; 
hence  it  is  necessary  to  use  tepid  water  in  the 
pneumatic  trough  or  gas-holder,  otherwise  great 
loss  of  gas  will  ensue.  Nitrous  oxide  has  been 
liquefied,  but  with  difficulty ;  it  requires,  at  45° 
(7°-2C)  a  pressure  of  50  atmospheres ;  the  liquid 
when  exposed  under  the  bell-glass  of  the  air-pump 
is  rapidly  converted  into  a  snow-like  solid.  When 
mixed  with  an  equal  volume  of  hydrogen,  and  fired 
by  the  electric  spark  in  the  eudiometer,  it  explodes 
with  violence,  and  liberates  its  own  measure  of  nitrogen.  Every  two  vol- 
umes of  the  gas  must  consequently  contain  two  volumes  of  nitrogen  and  one 
volume  of  oxygen,  the  whole  being  condensed  or  contracted  one-third;  a 
constitution  resembling  that  of  vapour  of  water.^ 

The  most  remarkable  feature  in  this  gas  is  its  intoxicating  power  upon  the 
animal  system.  It  may  be  respired,  if  quite  pure,  or  merely  mixed  with 
atmospheric  air,  for  a  short  time,  without  danger  or  inconvenience.  The 
effect  is  very  transient,  and  is  not  followed  by  depression. 

Binoxide  of  Nitrogen  ;  Nitric  Oxide.  —  Clippings  or  turnings  of  copper  are 
put  into  the  apparatus  employed  for  preparing  hydrogen,^  together  with  a 
little  water,  and  nitric  acid  added  by  the  funnel  until  brisk  efi"ervescence  is 
excited.  The  gas  may  be  collected  over  cold  wa  er,  as  it  is  not  sensibly 
soluble. 

The  reaction  is  a  simple  deoxidation  of  some  of  the  nitric  acid  by  the 
copper ;  the  metal  is  oxidized,  and  the  oxide  so  formed  is  dissolved  by  an- 


*  Florence  oil-flasks,  which  may  be  purchased  at  a  very  trifling  sum,  constitute  exceedingly 
useful  vessels  for  chemical  purposes,  and  often  supersede  retorts  or  other  expensive  appa- 
ratus. They  are  rendered  still  more  valuable  by  cutting  the  neck  smoothly  round  with  a 
hot  iron,  softening  it  in  the  flame  of  a  good  Argand  gas-lamp,  and  then  turning  over  the  edgo 
6o  as  to  form  a  lip,  or  border.  The  neck  will  then  bear  a  tight-fitting  cork  without  risk  of 
splitting. 

•  See  page  118.  •  See  page  111. 

11* 


120  NITROGEN. 

other  portion  of  the  acid.  Nitric  acid  is  Tery  prone  to  act  thus  upon  certain 
metals. 

The  gas  obtained  in  this  manner  is  colourless  and  transparent ;  in  contact 
with  air  or  oxygen  gas  it  produces  deep  red  fumes,  which  are  readily  ab- 
sorbed by  water ;  this  character  is  sufficient  to  distinguish  it  from  all  other 
gaseous  bodies.  A  lighted  taper  plunged  into  the  gas  is  extinguished ;  lighted 
phosphorus,  however,  burns  in  it  with  great  brilliancy. 

The  specific  gravity  of  binoxide  of  nitrogen  is  1039;  100  cubic  inches 
weigh  32-22  grains.  It  contains  equal  measures  of  oxygen  and  nitrogen 
gases  united  without  condensation.  When  this  gas  is  passed  into  a  solution 
of  protoxide  of  iron  it  is  absorbed  in  large  quantity,  and  a  deep  brown  or 
nearly  black  liquid  produced,  which  seems  to  be  a  definite  compound  of  the 
two  substances.     The  compound  is  again  decomposed  by  boiling. 

Nitrous  Acid. — Four  measures  of  binoxide  of  nitrogen  are  mixed  with  one 
measure  of  oxygen,  and  the  gases,  perfectly  dry,  exposed  to  a  temperature 
of  0°  ( — 17° -80).  They  condense  to  a  thin  mobile  green  liquid.  Its  vapour 
is  orange-red. 

Nitrous  acid  is  decomposed  by  water,  being  converted  into  nitric  acid  and 
binoxide  of  nitrogen.  For  this  reason  it  cannot  be  made  to  unite  directly 
with  metallic  oxides ;  nitrite  of  potassa  may,  however,  be  prepared  by  fusing 
nitrate  of  potassa,  when  part  of  its  oxygen  is  evolved ;  and  many  other  salts 
of  nitrous  acid  may  be  obtained  by  indirect  means. 

Hyponitric  Acid.  —  It  has  been  doubted  whether  the  term  acid  applied  to 
this  substance  be  correct,  since  it  seems  to  possess  the  power  of  forming  salts 
only  in  a  very  limited  degree;  the  expression  has,  notwithstanding,  been 
long  sanctioned  by  use.  Moreover,  a  beautiful  crystalline  lead-salt  of  this 
substance  has  been  discovered  by  M.  P^ligot.  It  is  formed  by  digesting 
nitrate  of  lead  with  metallic  lead. 

It  is  chiefly  the  vapour  of  hyponitric  acid  which  forms  the  deep  red  fumes 
always  produced  when  binoxide  of  nitrogen  escapes  into  the  air. 

When  carefully  dried  nitrate  of  lead  is  exposed  to  heat  in  a  retort  of  hard 
glass,  it  is  decomposed ;  protoxide  of  lead  remains  behind,  while  the  acid  is 
resolved  into  a  mixture  of  oxygen  and  hyponitric  acid.  By  surrounding  the 
receiver  with  a  very  powerful  freezing  mixture,  the  latter  is  condensed  to 
the  liquid  form.  It  is  then  nearly  colourless,  but  acquires  a  yellow,  and  ul- 
timately a  red  tint,  as  the  temperature  rises.  At  82°  (27°-8C)  it  boils, 
giving  off  its  well-known  red  vapour,  the  intensity  of  the  colour  of  which  is 
greatly  augmented  by  elevation  of  temperature. 

This  substance,  like  the  preceding,  is  decomposed  by  water,  being  resolved 
into  binoxide  of  nitrogen  and  nitric  acid.  Its  vapour  is  absorbed  by  strong 
nitric  acid,  which  thereby  acquires  a  yellow  or  red  tint,  passing  into  green, 
then  into  blue,  and  afterwards  disappearing  altogether  on  the  addition  of 
successive  portions  of  water.  The  deep  red  fuming  acid  of  commerce,  called 
nitrous  acid,  is  simply  nitric  acid  impregnated  with  hyponitric  gas.' 


Nitrogen  appears  to  combine,  under  favourable  circumstances,  with  metals 
When  iron  and  copper  are  heated  to  redness  in  an  atmosphere  of  ammonia, 
they  become  brittle  and  crystalline,  but  without  sensible  alteration  of  weight 
M.  Schrotter  has  shown  that  in  the  case  of  copper,  at  least,  this  effect  is 

*  Much  doubt  yet  hangs  over  the  true  nature  and  relations  of  these  two  acids.  According 
to  M.  P^ligot,  the  only  product  of  the  union  of  binoxide  of  nitrogen  and  oxygen  is  hyponitrii- 
acid,  which  in  the  total  absence  of  water  is  a  white  solid  crj'stalline  body,  fusible  at  16<^ 
(  — 8°-9Cy.  At  common  temperatures  it  is  an  orange-yellow  liquid.  The  same  product  is  ob- 
tained by  heating  perfectly  dry  nitrate  of  lead.  From  these  experiments  it  would  appear 
•^hat  nitrous  acid  in  a  separate  stafe  is  unknown.    Ann.  Chim.  et  Phys.  3d  series,  ii.  58. 


CARBON. 


12t 


cauged  by  the  formation  and  subsequent  destruction  of  a  nitride,  that  is,  a 
compound  of  nitrogen  with  copper.  When  ammonia  is  passed  over  protoxide 
of  copper  heated  to  570°  (298°-9C),  water  is  formed,  and  a  soft  brown 
powder  produced,  which  when  heated  farther  evolves  nitrogen,  and  leaves 
metallic  copper.  The  same  effect  is  produced  by  the  contact  of  strong  acids. 
A  similar  compound  of  chromium  with  nitrogen  appears  to  exist. 


This  substance  occurs  in  a  state  of  purity,  and  crystallized,  in  two  distinct 
and  very  dissimilar  forms,  namely,  as  diamond,  and  as  graphite  or  plumbago. 
It  constitutes  a  large  proportion  of  all  organic  structures,  animal  and  vege- 
table :  when  these  latter  are  exposed  to  destructive  distillation  in  close  ves- 
sels, a  great  part  of  this  carbon  remains,  obstinately  retaining  some  of  the 
hydrogen  and  oxygen,  and  associated  with  the  earthy  and  alkaline  matter  of 
the  tissue,  giving  rise  to  the  many  varieties  of  charcoal,  coke,  &c. 

The  diamond  is  one  of  the  most  remarkable  substances  known  ;  long  prized 
on  account  of  its  brilliancy  as  an  ornamental  gem,  the  discovery  of  its  curi- 
ous chemical  nature  confers  upon  it  a  high  degree  of  scientific  interest. 
Several  localities  in  India,  the  island  of  Borneo,  and  more  especially  Brazil, 
furnish  this  beautiful  substance.  It  is  always  distinctly  crystallized,  often 
quite  transparent  and  colourless,  but  now  and  then  having  a  shade  of  yellow, 
pink,  or  blue.  The  origin  and  true  geological  position  of  the  diamond  are 
unknown ;  it  is  always  found  embedded  in  gravel  and  transported  materials, 
whose  history  cannot  be  traced.  The  crystalline  form  of  the  diamond  is 
that  of  the  regular  octahedron  or  cube,  or  some  figure  geometrically  con- 
nected with  these ;  many  of  the  octahedral  crystals  exhibit  a  very  peculiar 
appearance,  arising  from  the  faces  being  curved  or  rounded,  which  gives  to 
the  crystal  an  almost  spherical  figure. 


Fig.  95. 


Fig.  96. 


Fig.  97 


Fig.  98. 


"  t" 


The  diamond  is  infusible  and  inalterable  by  a  very  intense  heat,  provided 
air  be  excluded;  but  when  heated,  thus  protected,  between  the  poles  of  a 
strong  galvanic  battery,  it  is  converted  into  coke  or  graphite ;  heated  to  or- 
dinary redness  in  a  vessel  of  oxygen,  it  burns  with  facility,  yielding  carbonic 
acid  gas. 

This  is  the  hardest  substance  known  ;  it  admits  of  being  split  or  cleaved 
without  difficulty  in  certain  particular  directions,  but  can  only  be  cut  or 
abraded  by  a  second  portion  of  the  same  material ;  the  powder  rubbed  off 
in  this  process  serves  for  polishing  the  new  faces,  and  is  also  highly  useful 
to  the  lapidary  And  seal-engraver.  One  very  curious  and  useful  application 
of  the  diamond  is  made  by  the  glazier ;  a  fragment  of  this  mineral,  like  a 
bit  of  flint,  or  any  other  hard  substance,  scratches  the  surface  of  glass  ;  a 
crystal  of  diamond  having  the  rounded  octahedral  figure  spoken  of,  held  in 
one  particular  position  on  the  glass,  namely,  with  an  edge  formed  by  the 
meeting  of  two  adjacent  faces  presented  to  the  surface,  and  then  drawn 
along  with  gentle  pressure,  causes  a  deep  split  or  cut,  which  penetrates  to 
a  considerable  depth  into  the  glass,  and  determines  its  fracture  with  perfect 
certainty. 


128  CARBON. 

Graphite,  or  plumbago,  appears  to  consist  essentially  of  pure  carbon,  al- 
though most  specimens  contain  iron,  the  quantity  of  which  varies  from  a 
mere  trace  up  to  five  per  cent.  Graphite  is  a  somewhat  rare  mineral ;  the 
finest,  and  most  valuable  for  pencils,  is  brought  from  Borrowdale,  in  Cum- 
berland, where  a  kind  of  irregular  vein  is  found  traversing  the  ancient  slate- 
beds  of  that  district.  Crystals  are  not  common ;  when  they  occur,  they 
have  the  figure  of  a  short  six-sided  prism; — a  form  bearing  no  geometric 
relation  to  that  of  the  diamond. 

Graphite  is  often  formed  artificially  in  certain  metallurgic  operations ;  the 
brilliant  scales  which  sometimes  separate  from  melted  cast  iron  on  cooling, 
called  by  the  workmen  "kish,"  consist  of  graphite. 

Lampblack,  the  soot  produced  by  the  imperfect  combustion  of  oil  or  resin, 
is  the  best  example  that  can  be  given  of  carbon  in  its  uncrystallized  or 
amorphous  state.  To  the  same  class  belong  the  difi"erent  kinds  of  charcoal. 
That  prepared  from  wood,  either  by  distillation  in  a  large  iron  retort,  or  by 
the  smothered  combustion  of  a  pile  of  fagots  partially  covered  with  earth, 
is  the  most  valuable  as  fuel.  Coke,  the  charcoal  of  pit-coal,  is  much  more 
impure ;  it  contains  a  large  quantity  of  earthy  matter,  and  very  often  sul- 
phur; the  quality  depending  very  much  upon  the  mode  of  preparation. 
Charcoal  from  bones  and  animal  matters  in  general  is  a  very  valuable  sub- 
stance, on  account  of  the  extraordinary  power  it  possesses  of  removing 
colouring  matters  from  organic  solutions ;  it  is  used  for  this  purpose  by  the 
sugar-refiners  to  a  very  great  extent,  and  also  by  the  manufacturing  and 
scientific  chemist.'  The  property  in  question  is  possessed  by  all  kinds  of 
charcoal  in  a  small  degree. 

Charcoal  made  from  box,  or  other  dense  wood,  has  a  property  of  con- 
densing into  its  pores  gases  and  vapours ;  of  ammoniacal  gas  it  is  said  to 
absorb  not  less  than  ninety  times  its  volume,  while  of  hydrogen  it  takes  up 
less  than  twice  its  own  bulk,  the  quantity  being  apparently  connected  with 
the  property  in  the  gas  of  suffering  liquefaction.  This  efi'ect,  as  well  as 
that  of  the  decolorizing  power,  no  doubt  depends  in  some  way  upon  the 
Bame  peculiar  action  of  surface  so  remarkable  in  the  case  of  platinum  in  a 
mixture  of  otygen  and  hydrogen.' 

Compounds  of  Carbon  and  Oxygen. 
There  are  two  direct  inorganic  compounds  of  carbon  and  oxygen,  called 
carbonic  oxide  and  carbonic  acid  ;  their  composition  may  be  thus  stated :  — 

Composition  by  weight. 


Carbon.  Oxygen,      o     r) 

Carbonic  oxide 6  ............     8        ^  i; 

Carbonic  acid 6  16-     d    O^ 

•  It  removes  fi-om  solution  in  water  the  vegetable  bases,  bitter  principles  and  astringent 
Bubstanccs,  when  employed  in  excess,  requiring  from  twice  to  twenty  times  their  weight  for 
total  precipitation.  A  solution  of  iodine  in  water,  or  iodide  of  potassium,  is  quickly  de- 
prived of  colour.  Metallic  salts  dissolved  in  water  or  diluted  alcohol  are  precipitated,  though 
not  entirely,  requiring  about  thirty  times  their  weight  of  animal  charcoal.  Arseuious  acid 
U  totally  carried  out  of  solution.  In  these  cases  it  acts  in  three  different  ways :  the  salt  is 
absorbed  unaltered;  the  oxide  in  the  salt  may  be  reduced;  or,  the  salts  precipitated  in  a 
ba.sic  condition,  the  solution  showing  an  acid  reaction  as  soon  as  the  carlx)n  begins  to  act.  It 
is  in  this  last  case  especially  that  traces  of  the  bases  can  be  detected,  the  acid  set  free  pre- 
venting their  total  precipitation.  The  precipitation  may  hence  be  prevented  by  adding  an 
excess  of  acid,  and  the  bases  after  precipitation  may  bo  dissolved  out  by  boiling  with  an  acid 
solution.  —  Warrington,  Mem.  Chim.  Soc.  1845;  Garrod,  Pharm.  Journ.  1845;  Weppen,  Ann. 
deChim.  1845.  — R.  B. 

•  Carbon  is  a  combustible  uniting  with  oxygen  and  producing  carbonic  acid.  Its  different 
forms  exhibit  much  difference  in  this  respect;  in  the  very  porous  condition  of  charcoal  it 
burns  readily,  while  in  its  most  dense  form,  the  diamond,  it  requires  a  bright  red  heat  and 
pure  oxygen.  In  the  form  of  charcoal  it  conducts  heat  slowly  and  electricity  readily.  Car- 
bon is  Insoluble  in  water  and  not  liable  to  be  affected  by  air  and  moisture.  It  retards  putr*> 
faction.  — R.B. 


CARBON 


m 


Carbonic  Acid  is  always  produced  when  charcoal  burns  in  air  or  in  oxygen 
gas ;  it  is  most  conveniently  obtained,  however,  for  study,  by  decomposing 
a  carbonate  with  one  of  the  stronger  acids.  For  this  purpose,  the  apparatus 
for  generating  hydrogen  may  be  again  employed ;  fragments  of  marble  are 
put  into  the  bottle,  with  enough  water  to  cover  the  extremity  of  the  funnel- 
tube,  and  hydrochloric  or  nitric  acid  added  by  the  latter,  until  the  gas  ifl 
freely  disengaged.  Chalk-powder  and  dilute  sulphuric  acid  may  be  used 
instead.     The  gas  may  be  collected  over  water,  although  with  some  loss ;  or 

Fig.  99. 


.>g^.i«i>=>e>!to^MaiVrVtVr'f^W«-Trlr- 


very  conveniently,  by  displacement,  if  it  be  required  dry,  as  shown  in  fig. 
99.  The  long  drying-tube  is  filled  with  fragments  of  chloride  of  calcium, 
and  the  heavy  gas  is  conducted  to  the  bottom  of  the  vessel  in  which  it  is  to 
be  received,  the  mouth  of  the  latter  being  lightly  closed.* 

Carbonic  acid  gas  is  colourless;  it  has  an  agreeable  pungent  taste  and 
odour,  but  cannot  be  respired  for  a  moment  without  insensibility  following. 
Its  specific  gravity  is  1-524,'  100  cubic  inches  weighing  47-26  grains. 

This  gas  is  very  hurtful  to  animal  life,  even  when  largely  diluted  with  air ; 
it  acts  as  a  narcotic  poison.  Hence  the  danger  arising  from  imperfect  ven- 
tilation, the  use  of  fire-places  and  stoves  of  all  kinds  unprovided  with  proper 
chimneys,  and  the  crowding  together  of  many  individuals  in  houses  and 
ships  without  efficient  means  for  renewing  the  air ;  for  carbonic  acid  is  con- 
stantly disengaged  during  the  process  of  respiration,  which,  as  we  have  seen, 
(page  108,)  is  nothing  but  a  process  of  slow  combustion.  This  gas  is  some- 
times emitted  in  large  quantity  from  the  earth  in  volcanic  districts,  and  it  is 
constantly  generated  where  organic  matter  is  in  the  act  of  undergoing  fer- 
mentive  decomposition.  The  fatal  "  after-damp"  of  the  coal-mines  contains 
a  large  proportion  of  carbonic  acid. 

•  In  connecting  tube-apparatus  for  conyeying  gases  or  cold  liquids,  not  corrosive,  little 
tubes  of  caoutchouc  about  an  inch  long,  are  in- 
expressibly useful.  These  are  made  by  bending 
a  piece  of  sheet  India-rubber,  a,  fig.  100,  loosely 
round  a  glass  tube  or  rod,  o,  and  cutting  off  the 
superfluous  portion  with  sharp  scissors.  The 
fresh-cut  edges  of  the  caoutchouc,  pressed  strongly 
together,  cohere  completely,  provided  they  have 
not  been  soiled  by  touching  with  the  fingers,  and 
the  tube  is  perfect.  The  connectors  are  secured 
by  two  or  three  turns  of  thin  silk  cord.  The 
glass  tubes  are  sold  by  weight,  and  are  easily 
bent  in  the  flame  of  a  spirit-lamp,  and,  when 
necessary,  cut  by  scratching  with  a  file,  and 
breaking  asunder. 

•  MM.  Dulong  and  Berzelius. 


Fig.  100. 


'30  CARBON, 

A  lighted  taper  plunged  into  carbonic  acid  is  instantly  extinguished,  even 
to  the  red-hot  snuff.  When  diluted  with  three  times  its  volume  of  air,  it 
still  has  the  power  of  extinguishing  a  light.  The  gas  is  easily  known  from 
nitrogen,  which  is  also  incapable  of  supporting  combustion,  by  its  rapid 
absorption  by  caustic  alkali  or  by  lime-water ;  the  turbidity  communicated 
to  the  latter  from  the  production  of  insoluble  carbonate  of  lime  is  very 
characteristic. 

Cold  water  dissolves  about  its  own  volume  of  carbonic  acid,  whatever  be 
the  density  of  the  gas  with  which  it  is  in  contact ;  the  solution  temporarily 
reddens  litmus  paper.  In  common  soda-water,  and  also  in  effervescent 
wines,  examples  may  be  seen  of  this  solubility  of  the  gas.  Even  boiling 
water  absorbs  a  perceptible  quantity. 

Some  of  the  interesting  phenomena  attending  the  liquefaction  of  carbonic 
acid  have  been  already  described ;  it  requires  for  the  purpose  a  pressure  of 
between  27  and  28  atmospheres  at  32°  (0°C),  according  to  Mr.  Addams. 
The  liquefied  acid  is  colourless  and  limpid,  lighter  than  water,  and  four 
times  more  expansible  than  air;  it  mixes  in  all  proportions  with  ether, 
alcohol,  naphtha,  oil  of  turpentine,  and  bisulphide  of  carbon,  and  is  insoluble 
in  water  and  fat  oils.  It  is  probably  destitute  when  in  this  condition  of  all 
properties  of  an  acid.' 

Carbonic  acid  exists,  as  already  mentioned,  in  the  air ;  relatively,  its  quan- 
tity is  but  small,  but  absolutely,  taking  into  account  the  vast  extent  of  the 
atmosphere,  it  is  very  great,  and  fully  adequate  to  the  purpose  for  which  it 
is  designed,  namely,  to  supply  to  plants  their  carbon,  these  latter  having 
the  power,  by  the  aid  of  their  green  leaves,  of  decomposing  carbonic  acid, 
retaining  the  carbon,  and  expelling  the  oxygen.  The  presence  of  light  is 
essential  to  this  extraordinary  effect,  but  of  the  manner  of  its  execution  we 
are  yet  ignorant. 

The  carbonates  form  a  very  large  and  important  group  of  salts,  some  of 
which  occur  in  nature  in  great  quantities,  as  the  carbonates  of  lime  and  mag- 
nesia. 

Carbonic  Oxide.  —  When  carbonic  acid  is  passed  over  red-hot  charcoal  or 
metallic  iron,  one-half  of  its  oxygen  is  removed,  and  it  becomes  converted 
into  carbonic  oxide.  A  very  good  method  of  preparing  this  gas  is  to  intro- 
duce into  a  flask  fitted  with  a  bent  tube  some  crystallized  oxalic  acid,  or  salt 
of  sorrel,  and  pour  upon  it  five  or  six  times  as  much  strong  oil  of  vitriol.- 
On  heating  the  mixture  the  organic  acid  is  resolved  into  water,  carbonic  acid, 
and  carbonic  oxide ;  by  passing  the  gases  through  a  strong  solution  of  caus- 
tic potassa,  the  first  is  withdrawn  by  absorption,  while  the  second  remains 
unchanged.  Another,  and  it  may  be  prefei'able  method,  is  to  heat  finely- 
powdered  yellow  ferrocyanide  of  potassium  with  eight  or  ten  times  its  weight 
of  concentrated  sulphuric  acid.  The  salt  is  entirely  decomposed,  yielding  a 
most  copious  supply  of  perfectly  pure  carbonic  oxide  gas,  which  may  be  col- 
lected over  water  in  the  usual  manner.^ 

Carbonic  oxide  is  a  combustible  gas ;  it  burns  with  a  beautiful  pale  blue 
6ame,  generating  carbonic  acid.  It  has  never  been  liquefied.  It  is  colour- 
less, has  very  little  odour,  and  is  extremely  poisonous,  even  worse  than 
carbonic  acid.     Mixed  with  oxygen,  it  explodes  by  the  electric  spark,  but 

•  When  relieved  of  pressure  it  immediately  boils,  and  seven  parts  out  of  eight  assume  the 
gaseous  state,  the  rest  becoming  solid  at  — 90°  (07°-7C)  (Mitchell).  Solid  carbonic  acid  mixed 
witli  ether  produces  in  vacuo  a  very  intense  cold  ( — 165°  [109°-4C]  Faraday),  capable  of 
solidifying  many  gases  when  aided  by  pressure.  Liquid  carbonic  acid  immersed  in  this  mix- 
ture becomes  a  solid  so  clear  and  transparent  that  its  condition  caunot  be  detected  until  a 
portion  again  becomes  liquid.  —  R.  B. 

'»  See  a  paper  by  the  author,  in  Memoirs  of  Chcm.  Soc.  of  London,  i.  251.  1  eq.  crystal- 
lized ferrocyanide  of  potassium,  and  6  eq.  oil  of  vitriol,  yield  6  eq.  carbonic  oxide,  2  eq.  suJ 
phate  of  potassa-  3  eq.  sulphate  of  ammonia,  and  1  eq.  protosulphate  of  iron. 


SU  LPHUR, 


131 


with  some  difficulty.  Its  specific  gravity  is  0-973 ;  100  cubic  inches  weigh 
30-21  grains. 

The  relation  by  volume  of  these  oxides  of  carbon  may  thus  be  made  in- 
telligible : — carbonic  acid  contains  its  own  volume  of  oxygen,  that  gas  suffer- 
ing no  change  of  bulk  by  its  conversion.  One  measure  of  carbonic  oxide 
mixed  with  half  a  measure  of  oxygen  and  exploded,  yields  one  measure  of 
carbonic  acid;  hence  carbonic  oxide  contains  half  its  volume  of  oxygen. 

Carbonic  oxide  unites  with  chlorine  under  the  influence  of  light,  forming 
a  pungent,  suflfocating  compound,  possessing  acid  properties,  called  phosgeno 
gas,  or  chioro-carbonic  acid.  It  is  made  by  mixing  equal  volumes  of  car- 
bonic oxide  and  chlorine,  both  perfectly  dry,  and  exposing  the  mixture  to 
sunshine ;  the  gases  unite  quietly,  the  colour  disappears,  and  the  volume 
becomes  reduced  to  one-half.     It  is  decomposed  by  water. 

SULPHUR. 

c      This  is  an  elementary  body  of  great  importance  and  interest.     Sulphur 

'is  often  found  in  a  free  state  in  connection  with  deposits  of  gypsum  and  rock- 
salt  ;  its  occurrence  in  volcanic  districts  is  probably  accidental.  Sicily  fur- 
nishes a  large  proportion  of  the  sulphur  employed  in  Europe.     In  a  state  of 

'  combination  with  iron  and  other  metals,  and  as  sulphuric  acid,  united  to 

"lime  and  magnesia,  it  is  also  abundant. 

Pure  sulphur  is  a  pale  yellow  brittle  solid,  of  well-known  appearance.  It 
melts  when  heated,  and  distils  over  unaltered,  if  air  be  excluded.  The  crys- 
tals of  sulphur  exhibit  two  distinct  and  incompatible  forms,  namely,  an  oc- 
tahedron with  rhombic  base  (fig.  101),  which  is  the  figure  of  native  sulphur, 
and  that  assumed  when  sulphur  separates  from  solution  at  common  tempe- 
ratures, as  when  a  solution  of  sulphur  in  bisulphide  of  carbon  is  exposed  to 
slow  evaporation  in  the  air;  and  a  lengthened  prism  (fig.  103),  having  no 
relation  to  the  preceding ;  this  happens  when  a  mass  of  sulphur  is  melted, 
and,  after  partial  cooling,  the  crust  at  the  surface  broken,  and  the  fluid  por 
tion  poured  out.     Fig.  102  shows  the  result  of  such  an  experiment. 

Pig.  101.  Fig.  102.  Fig.  103. 


The  specific  gravity  of  sulphur  varies  according  to  the  form  in  which  it  is 
crystallized.  The  octahedral  variety  has  a  specific  gravity  2-045 ;  the  pris- 
matic variety  a  specific  gravity  1-982. 

Sulphur  melts  at  232°  (111°-1C) ;  at  this  temperature  it  is  of  the  colour 
of  amber,  and  thin  and  fluid  as  water ;  when  farther  heated,  it  begins  to 
thicken,  and  to  acquire  a  deeper  colour;  and  between  430°  (221°C)  and  480° 
(249°C),  it  is  so  tenacious  that  the  vessel  in  which  it  is  contained  may  be 
inverted  for  a  moment  without  the  loss  of  its  contents.  If  in  this  state  it  be 
poured  into  water,  it  retains  for  many  hours  its  remarkable  soft  and  flexible 
condition,  which  should  be  looked  upon  as  the  amorphous  state  of  sulphur. 
After  a  while  it  again  becomes  brittle  and  crystalline.  From  the  tempera- 
ture last  mentioned  to  the  boiling-point,  about  792°  (400°C),  sulphur  again 


132  SULPHUR. 

becomes  thin  and  liquid.  In  the  preparation  of  commercial  flowers  of  sul- 
phur, the  vapour  is  conducted  into  a  large  cold  chamber,  where  it  condenses 
in  minute  crystals.     The  specific  gravity  of  sulphur-vapour  is  6-654. 

Sulphur  is  insoluble  in  water  and  alcohol ;  oil  of  turpentine  and  the  fat 
oils  dissolve  it,  but  the  best  substance  for  the  purpose  is  bisulphide  of  car- 
bon. In  its  chemical  relations  sulphur  bears  great  resemblance  to  oxygen ; 
to  very  many  oxides  there  are  corresponding  sulphides,  and  these  sulphides 
often  unite  among  themselves,  forming  crystallizable  compounds  analogous 
to  salts. 

Compounds  of  Sulphur  and  Oxygen. 

Composition  by  weight. 

Sulphur.  Oxygen- 
Sulphurous  acid 16 le^-j*-* 

Sulphuric  acid* 16  24 -'^•j 

Hyposulphurous  acid 32  16't>^®^ 

Hyposulphuric  acid 32  40-«^iOs- 

Sulphuretted  hyposulphuric  acid 48  40-Sj   Oj 

Bisulphuretted  hyposulphuric  acid* 64  .........  40^5  y  o 

Trisulphuretted  hyposulphuric  acid 80  40=  ^jg- ^ 

Sulphurous  Acid. — This  is  the  only  product  of  the  combustion  of  sulphur 
in  dry  air  or  oxygen  gas.  It  is  most  conveniently  prepared  by  heating  oil 
of  vitriol  with  metallic  mercury  or  copper  clippings;  a  portion  of  the  acid 
is  decomposed,  one-third  of  its  oxygen  being  transferred  to  the  metal,  while 
the  sulphuric  acid  becomes  sulphurous.  Sulphurous  acid  thus  obtained  is  a 
colourless  gas,  having  the  peculiar  suifocating  odour  of  burning  brimstone ; 
it  instantly  extinguishes  flame,  and  is  quite  irrespirable.  Its  density  is  2-21, 
100  cubic  inches  weighing  68-69  grains.  At  0°  ( — 17°-8C),  under  the  pres- 
sure of  the  atmosphere,  this  gas  condenses  to  a  colourless,  limpid  liquid, 
very  expansible  by  heat.  Cold  water  dissolves  rtore  than  thirty  times  its 
volume  of  sulphurous  acid.  The  solution  may  be  kept  unchanged  so  long 
as  air  is  excluded,  but  access  of  oxygen  gradually  converts  the  sulphurous 
into  sulphuric  acid,  in  the  presence  of  water,  although  the  dry  gases,  may 
remain  in  contact  for  any  length  of  time  without  change.  When  sulphurous 
acid  and  aqueous  vapour  are  passed  into  a  vessel  cooled  to  below  17°  or  21° 
( — 6°  or  — 8°C),  a  crystalline  body  forms,  which  contains  about  24-2  acid  to 
75-8  water. 

One  volume  of  sulphurous  acid  gas  contains  one  volume  of  oxygen,  and 
|th  of  a  volume  of  sulphur-vapour,  condensed  into  one  volume. 

Gases  which,  like  the  present,  are  freely  soluble  in  water,  must  be  col- 
lected by  displacement,  or  by  the  use  of  the  mercurial  pneumatic  trough. 

*  The  terminations  ous  and  ic,  applied  to  acids,  signify  degrees  of  oxidation,  the  latter  being 
the  highest;  acids  ending  in  cms  form  salts  the  names  of  which  are  made  to  end  in  ite.  and 
those  in  ic  terminate  in  ate,  as  sulphurous  acid,  sidphite,  of  soda,  sulphuric  acid,  sulphate  of 
Boda. 

*  The  more  advanced  student  will  be  glad  to  see  these  stated  in  equivalents  by  the  use  of 
symbols,  hereafter  to  be  explained,  their  relations  becoming  thereby  much  more  evident.  The 
liumbers  given  are  really  the  equivalent  numbers,  but  are  intended  only  to  show  the  pro- 
portions of  sulphur  and  oxygen,  without  any  reference  to  other  bodies.  The  following  are 
'he  quantities  required  to  saturate  one  equivalent  of  a  base : 

Sulphurous  acid SOu 

Sulphuric  acid SO3 

Hyposulphurous  acid SaOj  „ 

Hyposulphuric  acid,  Dithionic  add : SaOe 

Sulphuretted  hyposulphuric  acid,  Trithionic  acid SsOs 

Bisulphuretted  hyposulphuric  acid,  Tetrathionic  acid S4O9   . 

Trisulphuretted  hyposulphuric  acid,  Pentathionic  add SsO* 


SULPHUR.  133 

The  manipulation  with  the  latter  is  exactly  the  same  in  principle  as  with  the 
ordinary  water-trough,  but  rather  more  troublesome,  from  the  great  density 
of  the  mercury,  and  its  opacity.  The  whole  apparatus  is  on  a  much 
smaller  scale.  The  trough  is  best  constructed  of  hard,  sound  wood,  and  so 
contrived  as  to  economise  as  much  as  possible  the  expensive  fluid  it  is  to 
contain. 

Sulphurous  acid  has  bleaching  properties ;  it  is  used  in  the  arts  for  bleach- 
ing woollen  goods  and  straw-plait.  A  piece  of  blue  litmus-paper  plunged 
into  the  moist  gas  is  first  reddened  and  then  slowly  bleached. 

The  salts  of  sulphurous  acid  are  not  of  much  importance ;  those  of  the 
alkalis  are  soluble  and  crystallizable ;  they  are  easily  formed  by  direct  com- 
bination. Sulphites  of  baryta,  strontia,  and  lime,  are  insoluble  in  water, 
but  soluble  in  hydrochloric  acid.  The  strong  acids  decompose  them ;  nitric 
acid  converts  them  into  sulphates. 

Sulphuric  Add.  —  Hydrated  sulphuric  acid  has  been  known  since  the 
fifteenth  century.  There  are  two  distinct  processes  by  which  it  is  at  the 
present  time  prepared,  namely,  by  the  distillation  of  green  sulphate  of  iron, 
and  by  the  oxidation  of  sulphurous  acid  by  nitrous  acid. 

The  first  process  is  still  carried  on  in  some  parts  of  Germany,  especially 
in  the  neighbourhood  of  Nordhausen  in  Prussia ;  the  sulphate  of  iron,  derived 
from  the  oxidation  of  iron  pyrites,  is  deprived  by  heat  of  the  greater  part 
of  its  water  of  crystallization,  and  subjected  to  a  high  red  heat  in  earthen 
retorts,  to  which  receivers  are  fitted  as  soon  as  the  acid  begins  to  distil  over. 
A  part  gets  decomposed  by  the  very  high  temperature ;  the  remainder  is 
driven  off  in  vapour,  which  is  condensed  by  the  cold  vessel.  The  product  is 
a  brown  oily  liquid,  of  about  1-9  specific  gravity,  fuming  in  the  air,  and  very 
corrosive.     It  is  chiefly  made  for  the  purpose  of  dissolving  indigo. 

The  second  method,  which  is  perhaps,  with  the  single  exception  mentioned, 
always  followed  as  the  more  economical,  depends  upon  the  fact,  that,  when 
sulphurous  acid,  hyponitric  acid,  and  water  are  present  in  certain  propor- 
tions, the  sulphurous  acid  becomes  oxidized  at  the  expense  of  the  hyponitric 
acid,  which  by  the  loss  of  one-half  of  its  oxygen  sinks  to  the  condition  of 
binoxide  of  nitrogen.  The  operation  is  thus  conducted :  — A  large  and  very 
long  chamber  is  built  of  sheet-lead  supported  by  timber  framing ;  on  the 
outside,  at  one  extremity,  a  small  furnace  or  oven  is  constructed,  having  a 
wide  tube  leading  into  the  chamber.  In  this  sulphur  is  kept  burning,  the 
flame  of  which  heats  a  crucible  containing  a  mixture  of  nitre  and  oil  of 
vitriol.  A  shallow  stratum  of  water  occupies  the  floor  of  the  chamber, 
and  sometimes  a  jet  of  steam  is  also  introduced.  Lastly,  an  exit  is  provided 
at  the  remote  end  of  the  chamber  for  the  spent  and  useless  gases.  The 
effect  of  these  arrangements  is  to  cause  a  constant  supply  of  sulphurous 
acid,  atmospheric  air,  nitric  acid  vapour,  and  water  in  the  state  of  steam, 
to  be  thrown  into  the  chamber,  there  to  mix  and  react  upon  each  other. 
The  nitric  acid  immediately  gives  up  a  part  of  its  oxygen  to  the  sulphurous 
acid,  becoming  hyponitric ;  it  does  not  remain  in  this  state,  however,  but 
suffers  farther  deoxidation  until  it  is  reduced  to  binoxide  of  nitrogen.  That 
substance  in  contact  with  free  oxygen  absorbs  a  portion  of  the  latter,  and 
once  more  becomes  hyponitric  acid,  which  is  again  destined  to  undergo  de- 
oxidation  by  a  fresh  quantity  of  sulphurous  acid.  A  very  small  portion  of 
hyponitric  acid,  mixed  with  atmospheric  air  and  sulphurous  acid,  may  thus 
in  time  convert  an  indefinite  amount  of  the  latter  into  sulphuric  acid,  by 
acting  as  a  kind  of  carrier  between  the  oxygen  of  the  air  and  the  sulphurous 
acid.     The  presence  of  water  is  essential  to  this  reaction. 

We  may  represent  the  change  by  the  diagram  on  the  succeeding  page :  — 
12 


134  SULPHUR. 

{Nitrogen  14 ^  Binoxide  of  nitrogen  30 
Oxygen     16 
Oxygen     16^ 

Sulphurous  acid  64{«"^';g'--^|; 

Water  .." 18 —     ''^>  Hydrated  sulphuric  acid  98 

Such  is  the  simplest  view  that  can  be  taken  of  the  production  of  sulphuric 
acid  in  the  leaden  chamber,  but  it  is  too  much  to  affirm  that  it  is  strictly 
true ;  it  may  be  more  complex.  When  a  little  water  is  put  at  the  bottom  of 
a  large  glass  globe,  so  as  to  maintain  a  certain  degree  of  humidity  in  the 
air  within,  and  sulphurous  and  hyponitric  acids  are  introduced  by  separate 
tubes,  symptoms  of  chem  cal  action  become  immediately  evident,  and  after 
a  little  time  a  white  crystalline  matter  is  observed  to  condense  on  the  sides 
of  the  vessel.  This  substance  appears  to  be  a  compound  of  sulphui'ic  acid, 
nitrous  acid,  and  a  little  water.'  When  thrown  into  water,  it  is  resolved  into 
sulphuric  acid,  binoxide  of  nitrogen,  and  nitric  acid.  This  curious  body  is 
certainly  very  often  produced  in  large  quantity  in  the  leaden  chambers ;  but 
that  its  production  is  indispensable  to  the  success  of  the  process,  and  con- 
stant when  the  operation  goes  on  well,  and  the  hyponitric  acid  is  not  in 
excess,  may  perhaps  admit  of  doubt. 

The  water  at  the  bottom  of  the  chamber  thus  becomes  loaded  with  sul- 
phuric acid ;  when  a  certain  degree  of  strength  has  been  reached,  it  is  drawn 
oflF  and  concentrated  by  evaporation,  first  in  leaden  pans,  and  afterwards  in 
stills  of  platinum,  until  it  attains  a  density  (when  cold)  of  1-84,  or  there- 
abouts ;  it  is  then  transferred  to  carboys,  or  large  glass  bottles  fitted  in  bas- 
kets, for  sale.  In  Great  Britain  this  manufacture  is  one  of  great  national 
importance,  and  is  carried  on  to  a  vast  extent.  An  inferior  kind  of  acid  is 
sometimes  made  by  burning  iron  pyrites,  or  poor  copper  ore,  as  a  substitute 
for  Sicilian  sulphur;  this  is  chiefly  used  by  the  makers  for  their  own  con- 
sumption ;  it  very  frequently  contains  arsenic.  ' 

The  most  concentrated  sulphuric  acid,  or  oil  of  vitriol,  as  it  is  often  called, 
is  a  definite  combination  of  40  parts  real  acid,  and  9  parts  water.  It  is  a 
colourless,  oily  liquid,  having  a  specific  gravity  of  about  1-85,  of  intensely 
acid  taste  and  reaction.  Organic  matter  is  rapidly  charred  and  destroyed 
by  this  substance.  At  the  temperature  of — 15°  ( — 26°'1C)  it  freezes;  at 
620°  (326° '60)  it  boils,  and  may  be  distilled  without  decomposition.  Oil  of 
vitriol  has  a  most  energetic  attraction  for  water;  it  withdraws  aqueous 
vapours  from  the  air,  and  when  diluted,  gi'eat  heat  is  evolved,  so  that  the 
mixture  always  requires  to  be  made  with  caution.  Oil  of  vitriol  is  not  the 
only  hydrate  of  sulphuric  acid ;  three  others  are  known  to  exist.  When  the 
fuming  oil  of  vitriol  of  Nordhausen  is  exposed  to  a  low  temperature,  a  white 
crystalline  substance  Separates,  which  is  a  hydrate  containing  half  as  much 
water  as  the  common  liquid  acid.  Then,  again,  a  mixture  of  49  parts  strong 
liquid  acid  and  9  parts  water,  congeals  or  crystallizes  at  a  temperature  above 

*  M.  Gaultier  de  Claubry  assigned  to  this  curious  substance  the  composition  expressed  hy 
the  formula  4H0,  2NOs+5S03,  and  this  view  has  generally  been  received  by  recent  chemical 
writers.  M.  de  la  Provostaye  has  since  shown  that  a  compound,  possessing  all  the  essential 
properties  of  the  body  in  question,  may  be  formed  by  bringing  together,  in  a  sealed  glass 
tube,  liquid  sulphurous  acid  and  liquid  hyponitric  axiid,  both  free  from  water.  The  white 
crystalline  solid  soon  begins  to  form,  and  at  the  expiration  of  twenty-six  hours  the  reaction 
appears  complete.  The  new  product  is  accompanied  by  an  exceedingly  volatile  greenish 
liquid  having  the  characters  of  nitrous  acid.  The  white  substance,  on  analysis,  was  found 
to  contain  the  elements  of  two  equivalents  of  sulphuric  acid  and  one  of  nitrous  acid,  or 
NO3+2SO3.  M.  de  la  Provostaye  very  ingeniously  explains  the  anomalies  in  the  diflerent 
analyses  of  the  leaden  chamber  product,  by  showing  that  the  pure  substance  forms  crystal- 
lizable  combinations  with  different  proportions  of  liquid  sulphuric  acid.  (Ann.  Ohim.  et 
Fbys.  Ixxiii.  362.) 


SULPHUR.  135 

32°  (0°C),  and  remains  solid  even  at  45°  (7°-2C).  Lastly,  when  a  very 
dilute  acid  is  concentrated  by  evaporation  in  vacuo  over  a  surface  of  oil  of 
vitriol,  the  evaporation  stops  when  the  real  acid  and  water  bear  to  each 
other  the  proportion  of  40  to  27. 

When  good  Nordhausen  oil  of  vitriol  is  exposed  in  a  retort  to  a  gentle 
heat,  and  a  receiver  cooled  by  a  freezing  mixture  fitted  to  it,  a  volatile 
substance  distils  over  in  great  abundance,  which  condenses  into  beautiful, 
white,  silky  crystals,  resembling  those  of  asbestus ;  this  bears  the  name  of 
anhydrous  sulphuric  acid.  When  put  into  water  it  hisses  like  a  hot  iron, 
from  the  violence  with  which  combination  occurs ;  exposed  to  the  air  even 
for  a  few  moments,  it  liquefies  by  absorption  of  moisture,  forming  common 
liquid  sulphuric  acid.  It  forms  an  exceedingly  curious  compound  with  dry 
ammoniacal  gas,  quite  distinct  from  ordinary  sulphate  of  ammonia,  and 
which  indeed  possesses  none  of  the  characters  of  a  sulphate.  This  interest- 
ing substance  may  also  be  obtained  by  distilling  the  most  concentrated  oil 
of  vijtriol  with  a  sufficient  quantity  of  anhydrous  phosphoric  acid. 

Sulphuric  acid,  in  all  soluble  states  of  combination,  may  be  detected  with 
the  greatest  ease  by  solution  of  nitrate  of  baryta,  or  chloride  of  barium.  A 
white  precipitate  is  produced,  which  does  not  dissolve  in  nitric  acid. 

Hyposulphurous  Acid. — By  digesting  sulphur  with  a  solution  of  sulphite 
of  potassa  or  soda,  a  portion  of  that  substance  is  dissolved,  and  the  liquid, 
by  slow  evaporation,  furnishes  crystals  of  the  new  salt.  The  acid  cannot  be 
isolated ;  when  hydrochloric  acid  is  added  to  a  solution  of  a  hyposulphite, 
the  acid  of  the  latter  is  almost  instantly  resolved  into  sulphur,  which  pre- 
cipitates, and  into  sulphurous  acid,  easily  recognized  by  its  odour.  The 
most  remarkable  feature  of  the  alkaline  hyposulphites  is  their  property  of 
dissolving  certain  insoluble  salts  of  silver,  as  the  chloride — a  property  which 
has  lately  conferred  upon  them  a  considerable  share  of  importance  in  rela- 
tion to  the  art  of  photogenic  drawing. 

Hyposulphuric  Acid,  Dithionic  Acid. — This  is  prepared  by  suspending 
finely  divided  binoxide  of  manganese  in  water  artificially  cooled,  and  then 
transmitting  a  stream  of  sulphurous  acid  gas ;  the  binoxide  becomes  pro- 
toxide, half  its  oxygen  converting  the  sulphurous  acid  into  hyposulphuric. 
The  hyposulphate  of  manganese  thus  prepared  is  decomposed  by  a  solution 
of  pure  hydrate  of  baryta,  and  the  barytic  salt,  in  turn,  by  enough  sul- 
phuric acid  to  precipitate  the  base.  The  solution  of  hyposulphuric  acid 
may  be  concentrated  by  evaporation  in  vacuo,  until  it  acquires  a  density  of 
1-347:  pushed  farther,  it  decomposes  into  sulphuric  and  sulphurous  acids. 
It  has  no  odour,  is  very  sour,  and  forms  soluble  salts  with  baryta,  lime,  and 
protoxide  of  lead. 

Sulphuretted  hyposulphuric  Acid,  Trithionic  Acid. — A  substance  accidentally 
formed  by  M.  Langlois,'  in  the  preparation  of  hyposulphite  of  potassa,  by 
gently  heating  with  sulphur  a  solution  of  carbonate  of  potassa,  saturated 
with  sulphurous  acid.  The  salts  bear  a  great  resemblance  to  tliose  of  hypo- 
sulphurous  acid,  but  differ  completely  in  composition,  while  the  acid  itself 
is  not  quite  so  prone  to  change.  It  is  obtained  by  decomposing  the  potassa 
salt  by  hydrofluosilicic  acid  ;  it  may  be  concentrated  under  the  receiver  of 
the  air-pump,  but  it  is  gradually  decomposed  into  sulphur,  sulphurous  and 
sulphuric  acids. 

Bisulphuretted  hypositvphuric  Acid,  Tetrathionic  Acid.  — This  was  discovered 
by  MM.  Fordos  and  G61is.»  When  iodine  is  added  to  a  solution  of  hyposul- 
pVit*^  of  soda,  a  large  quantity  of  that  substance  is  dissolved,  and  a  cleai, 
rvv  p^ess  solution  obtained,  which,  besides  iodide  of  sodium,  contains  a  salt 


»  Ann.  Chim.  et  Phys.  3d  sanes,  iv.  77. 
•  27;.  3(1  serie?.  vi.  ii4r- 


136  SELENIUM. 

of  a  peculiar  acid,  richer  in  sulphur  than  the  preceding.  By  suitable  means, 
the  new  substance  can  be  eliminated,  and  obtained  in  a  state  of  solution. 
It  very  closely  resembles  hyposulphuric  acid.  The  same  acid  is  produced  by 
the  action  of  sulphurous  acid  on  subchloride  of  sulphur. 

Trisulplmretled  hypomlphuric  Acid,  Pentathionic  Acid.  —  Another  acid  of 
sulphur  has  been  announced  by  M.  Wackenroder,  who  foi-med  it  by  the 
action  of  sulphuretted  hydrogen  on  sulphurous  acid.  It  is  described  as 
colourless  and  inodorous,  of  acid  and  bitter  taste,  and  capable  of  being  con- 
centrated to  a  considerable  extent  by  cautious  evaporation.  It  contains  S5O5 ; 
under  the  influence  of  heat,  it  is  decompo&ed  into  sulphur,  sulphurous  and 
sulphuric  acid  and  sulphuretted  hydrogen.  The  salts  of  pentathionic  acids 
are  nearly  all  soluble.  The  baryta  salt  crystallizes  from  alcohol  in  square 
prisms.  The  acid  is  also  formed  when  hyposulphate  of  lead  is  decomposed 
by  sulphuretted  hydrogen,  and  when  protochloride  of  sulphur  is  heated  with 
sulphurous  acid. 

Sulphurous  acid  unites,  under  peculiar  circumstances,  with  chlorine,  and 
also  with  iodine,  forming  compounds,  which  have  been  called  chloro-  and 
iodo-sulphuric  acids.  They  are  decomposed  by  water.  It  also  combines 
with  dry  ammoniacal  gas,  giving  rise  to  a  remarkable  compound ;  and  with 
nitric  oxide  also,  in  presence  of  an  alkali. 

SELENIUM. 

This  is  a  very  rare  substance,  much  resembling  sulphur  in  its  chemical 
relations,  and  found  in  association  with  that  element  in  some  few  localities, 
or  replacing  it  in  certain  metallic  combinations,  as  in  the  selenide  of  lead  of 
Clausthal,  in  the  Hartz. 

Selenium  is  a  reddish-brown  solid  body,  somewhat  translucent,  and  having 
an  imperfect  metallic  lustre.  Its  specific  gravity,  when  rapidly  cooled  after 
fusion,  is  4-3.  At  212°  (lOOoC),  or  a  little  above,  it  melts,  and  at  650° 
(343° -30)  boils.  It  is  insoluble  in  water,  and  exhales,  when  heated  in  the 
air,  a  peculiar  and  disagreeable  odour,  which  has  been  compared  to  that  of 
decaying  horseradish.  Ther^  are  three  oxides  of  selenium,  two  of  which 
correspond  respectively  to  sulphurous  and  sulphuric  acids,  while  the  thii-d 
has  no  known  analogue  in  the  sulphur  series. 

Composition  by  weight 
Selenium.         Oxygen. 

Oxide  of  selenium  39-6  8 

Selenious  acid  39-5  16 

Selenic  acid  ., 39-5  24 

Oxide. — Formed  by  heating  selenium  in  the  air.  It  is  a  colourless  gas, 
slightly  soluble  in  water,  and  has  the  remarkable  odour  above  described.  It 
has  no  acid  properties. 

Selenious  Acid. — This  is  obtained  by  dissolving  selenium  in  nitric  acid,  and 
evaporating  to  dryness.  It  is  a  white,  soluble,  deliquescent  substance,  of 
distinct  acid  properties,  and  may  be  sublimed  without  decomposition.  Sul- 
phurous acid  decomposes  it,  precipitating  the  selenium. 

Selenic  Acid. — Prepared  by  fusing  nitrate  of  potassa  or  soda  with  selenium, 
precipitating  the  seleniate  so  produced  by  a  salt  of  lead,  and  then  decom- 
posing the  compound  by  sulphuretted  hydrogen.  The  hydrated  acid  strongly 
resembles  oil  of  vitriol ;  but,  when  very  much  concentrated,  decomposes,  by 
the  application  of  heat,  into  selenious  acid  and  oxygen.  The  seleniates  bear 
<he  closest  analogy  to  the  sulphates  in  every  particular. 


PHOSPHORUS 


ISt 


PHOSPHORUS. 

Phosphorus  in  a  state  of  phosphoric  acid  is  contained  in  the  ancient  un- 
Btratified  rocks,  and  in  the  lavas  of  modern  origin.  As  these  disintegrate  and 
crumble  down  into  fertile  soil,  the  phosphates  pass  into  the  organism  of 
plants,  and  ultimately  into  the  bodies  of  the  animals  to  which  these  latter 
serve  for  food.  The  earthy  phosphates  play  a  very  important  part  in  the 
structure  of  the  animal  frame,  by  communicating  stiffness  and  inflexibility 
to  the  bony  skeleton. 

This  element  was  discovered  in  1669  by  Brandt,  of  Hamburg,  who  pre- 
pared it  from  urine.  The  following  is  an  outline  of  the  process  now  adopted. 
Thoroughly  calcined  bones  are  reduced  to  powder,  and  mixed  with  two- 
thirds  of  their  weight  of  sulphuric  acid,  diluted  with  a  considerable  quantity 
of  water ;  this  mixture,  after  standing  some  hours,  is  filtered,  and  the  nearly 
Insoluble  sulphate  of  lime  washed.  The  liquid  is  then  evaporated  to  a 
syrupy  consistence,  mixed  with  charcoal  powder,  and  the  desiccation  com- 
pleted in  an  iron  vessel  exposed  to  a  high  temperature.  "When  quite  dry, 
it  is  transferred  to  a  stoneware  retort,  to  which  a  wide  bent  tube  is  luted, 
dipping  a  little  way  into  the  water  contained  in  the  receiver.  A  narrow  tube 
(Serves  to  give  issue  to  the  gases,  which  are  con- 
veyed to  a  chimney.  (Fig.  104.)  This  manufac-  Fig.  104. 
ture  is  now  conducted  on  a  very  great  scale,  the 
consumption  of  phosphorus,  for  the  apparently 
trifling  article  of  instantaneous  light  matches, 
being  something  prodigious. 

Phosphorus,  when  pure,  very  much  resembles 
in  appearance  imperfectly  bleached  wax,  and  is 
soft  and  flexible  at  common  temperatures.  Its 
density  is  1-77,  and  that  of  its  vapour  4-35,  air 
being  unity.  At  108°  (42°-2C)  it  melts,  and  at 
550°  (287°-7C)  boils.  It  is  insoluble  in  water, 
and  is  usually  kept  immersed  in  that  liquid,  but 
dissolves  in  oils,  in  native  naphtha,  and  especially 
in  bisulphide  of  carbon.  When  set  on  fire  in 
the  air,  it  burns  with  a  bright  flame,  generating 
phosphoric  acid.  Phosphorus  is  exceedingly  in- 
flammable ;  it  sometimes  takes  fire  by  the  heat 
of  the  hand,  and  demands  great  care  in  its  management ;  a  blow  or  hard 
rub  will  very  often  kindle  it.  A  stick  of  phosphorus  held  in  the  air  always 
appears  to  emit  a  whitish  smoke,  which  in  the  dark  is  luminous.  This  eff'ect 
is  chiefly  due  to  a  slow  combustion  which  the  phosphorus  undergoes  by  the 
oxygen  of  the  air,  and  upon  it  depends  one  of  the  methods  employed  for  the 
analysis  of  the  atmosphere,  as  already  described.  It  is  singular  that  the 
slow  oxidation  of  phosphorus  may  be  entirely  prevented  by  the  presence  of 
a  small  quantity  of  defiant  gas,  or  the  vapour  of  ether,  or  some  essential 
oil;  it  may  even  be  distilled  in  an  atmosphere  containing  vapour  of  oil  of 
turpentine  in  considerable  quantity.  Neither  does  the  action  go  on  in  pui*e 
oxygen,  at  least  at  the  temperature  of  60°  (15°-5C),  whicli  is  very  remark- 
able ;  but  if  the  gas  be  rarefied,  or  diluted  with  nitrogen,  hydrogen,  or  car 
bonic  acid,  oxidation  is  set  up.  According  to  the  researches  of  MarchanJ, 
evaporation  of  phosphorus  causes  a  luminosity,  even  when  there  is  no  ox'da- 
tion. 

A  very  remarkable  modification  of  this  element  is  known  by  the  name  ol 

amorphous  phosphorus.     It  was  discovered  by  Schrotter,  and  may  be  made 

by  exposing  for  fifty  hours  common  phosphorus  to  a  temperature  of  about 

464°  to  482°  (240°  to  250°C)  in  an  atmosphere  which  is  unable  to  act  chemi- 

12  * 


138  PHOSPHORUS. 

cally  upon  it.  At  this  temperature  it  becomes  red  and  opaque,  and  insoluble 
in  bisulphide  of  carbon,  whereby  it  may  be  separated  from  ordinary  phos- 
phorus. It  may  be  obtained  in  compact  masses  when  common  phosphorus 
is  kept  for  eight  days  at  a  constant  high  temperature.  It  is  a  coherent, 
reddish-brown,  infusible  substance,  of  specific  gravity  between  2-089  and 
2106.  It  does  not  become  luminous  in  the  dark  until  its  temperature  is 
raised  to  about  392°  (200°C),  nor  has  it  any  tendency  to  combine  with  the 
oxygen  of  the  air.  When  heated  to  500°  (260°C),  it  is  reconverted  into 
ordinary  phosphorus. 

Compounds  of  Phosphorus  and  Oxygen.  —  These  are  four  in  number,  and 
have  the  composition  indicated  below. 

Composition  by  weight. 

Pliosphorus.      Oxygen. 

Oxide  of  phosphorus  64 8 

Hypophosphorous  acid 32  8 

Phosphorous  acid  32  24 

Phosphoric  acid  *  32  40 

Oxide  of  Phosphorus. — When  phosphorus  is  melted  beneath  the  surface  of 
hot  water,  and  a  stream  of  oxygen  gas  forced  upon  it  from  a  bladder,  com- 
bustion ensues,  and  the  phosphorus  is  converted  in  great  part  into  a  brick- 
red  powder,  which  is  the  substance  in  question.  It  is  decomposed  by  heat 
into  phosphorus  and  phosphoric  acid. 

Hypophosphorous  Acid. — When  phosphide  of  barium  is  put  into  hot  water, 
that  liquid  is  decomposed,  giving  rise  to  phosphoretted  hydrogen,  phos- 
phoric acid,  hypophosphorous  acid,  and  baryta ;  the  first  escapes  as  gas,  and 
the  two  acids  remain  in  union  with  the  baryta.  By  filtration  the  soluble 
hypophosphite  is  separated  from  the  insoluble  phosphate.  On  adding  to  the 
liquid  the  quantity  of  sulphuric  acid  necessary  to  precipitate  the  base,  the 
hypophosphorous  acid  is  obtained  in  solution.  By  evaporation  it  may  be 
reduced  to  a  syrupy  consistence. 

The  acid  is  very  prone  to  absorb  more  oxygen,  and  is  therefore  a  powerful 
deoxidizing  agent.     All  its  salts  are  soluble  in  water. 

Phosphorous  Acid. — Phosphorous  acid  is  formed  by  the  slow  combustion 
of  phosphorus  in  the  atmosphere ;  or  by  burning  that  substance  by  means 
of  a  very  limited  supply  of  air,  in  which  case  it  is  anhydrous,  and  presents 
the  aspect  of  a  white  powder.  The  hydrated  acid  is  more  conveniently 
prepared  by  adding  water  to  the  terchloride  of  phosphorus,  when  mutual 
decomposition  takes  place,  the  oxygen  of  the  water  being  transferred  to  the 
phosphorus,  generating  phosphorous  acid,  and  its  hydrogen  to  the  chlonne, 
giving  rise  to  hydrochloric  acid.  By  evaporating  the  solution  to  the  con- 
sistence of  syrup,  the  hydrochloric  acid  is  expelled,  and  the  residue  on 
cooling  crystallizes. 

Hydrated  phosphorous  acid  is  very  deliquescent  and  very  prone  to  attract 
oxygen  and  pass  into  phosphoric  acid.  When  heated  in  a  close  vessel,  it  i3 
resolved  into  hydrated  phosphoric  acid  and  pure  phosphoretted  hydrogen  gas. 
It  is  composed  of  56  parts  real  acid  and  27  parts  water.  ' 

The  phosphites  are  of  little  importance. 

Phosphoric  Acid. — When  phosphorus  is  burned  under  a  bell-jar  by  the  aid 
ef  a  copious  supply  of  dry  air,  snow-like  anhydrous  phosphoric  acid  is  pro- 

» In  symbols— Oxifle  of  phosphorus PaO 

Hypophosphorous  acid V  0 

Pliosphorous  acid P  Os 

Phosphoric  acid  P  Ob 

Equivalent  of  phosphorus,  32 

3  0r,  3nO,  P03. 


CHLORINE. 


139 


duced  in  great  quantity.  This  substance  exhibits  as  much  attraction  for 
water  as  anhydrous  sulphuric  acid ;  exposed  to  the  air  for  a  few  moments, 
it  deliquesces  to  a  liquid,  and  when  thrown  into  water,  combines  with  the 
latter  with  explosive  violence.  Once  in  the  state  of  hydrate,  the  water 
cannot  again  be  separated. 

When  nitric  acid  of  moderate  strength  is  heated  in  a  retort  to  which  a 
receiver  is  connected,  and  fragments  of  phosphorus  added  singly,  taking 
care  to  suffer  the  violence  of  the  action  to  subside  between  each  addition, 
the  phosphorus  is  oxidized  to  its  maximum,  and  converted  into  phosphoric 
acid.  By  distilling  off  the  greater  part  of  the  acid,  transferring  the  residue 
In  the  retort  to  a  platinum  vessel,  and  then  cautiously  raising  the  heat  to 
redness,  the  hydrated  acid  may  be  obtained  pure.  This  is  the  glacial  phos- 
phoric acid  of  the  Pharmacopoeia. 

A  third  method  consists  in  taking  the  acid  phosphate  of  lime  produced  by 
the  action  of  sulphuric  acid  on  bone-earth,  precipitating  it  with  a  slight 
excess  of  carbonate  of  ammonia,  separating  by  a  filter  the  insoluble  lime- 
salt,  and  then  evaporating  and  igniting  in  a  platinum  vessel  the  mixed 
phosphate  and  sulphate  of  ammonia.  Hydrated  phosphoric  acid  alone  remains 
behind.  The  acid  thus  obtained  is  not  remarkable  for  its  purity.  One  of 
the  most  advantageous  methods  of  preparing  phosphoric  acid  on  the  large 
scale  in  a  state  of  purity,  is  to  burn  phosphorus  in  a  stream  of  dry  atmo- 
spheric air,  by  the  aid  of  a  proper  apparatus,  not  difficult  to  contrive,  in 
which  the  process  may  be  carried  on  continuously.  The  anhydrous  acid 
obtained  may  be  preserved  in  that  state,  or  converted  into  hydrate  or  glacial 
acid,  by  the  addition  of  water  and  subsequent  fusion  in  a  platinum  vessel. 
The  hydrate  of  phosphoric  acid  is  exceedingly  deliquescent,  and  requires  to 
be  kept  in  a  closely  stopped  bottle.  It  contains  72  parts  real  acid,  and  9 
parts  water. 

Phosphoric  acid  is  a  powerful  acid ;  its  solution  has  an  intensely  sour 
taste,  and  reddens  litmus  paper ;  it  is  not  poisonous. 

There  are  few  bodies  that  present  a  greater  degree  of  interest  to  the 
chemist  than  this  substance  ;  the  extraordinary  changes 
its  compounds  undergo  by  the  action  of  heat,  chiefly  ^S- 105* 

made  known  to  us  by  the  admirable  researches  of 
Prof.  Graham,  will  be  found  described  in  connection 
with  the  general  history  of  saline  compounds. 

CHLORINE. 

This  substance  is  a  member  of  a  small  natural  group 
containing  besides  iodine,  bromine  and  fluorine.  So 
great  a  degree  of  resemblance  exists  between  these 
bodies  in  all  their  chemical  relations,  that  the  history 
of  one  will  almost  serve,  with  a  few  little  alterations, 
for  that  of  the  rest. 

Chlorine'  is  a  very  abundant  substance  ;  in  common 
salt  it  exists  in  combination  with  sodium.  It  is  most 
easily  prepared  by  pouring  strong  liquid  hydrochloric 
acid  upon  finely-powdered  black  oxide  of  manganese, 
contained  in  a  ret(/  ,  or  flask,  and  applying  a  gentle 
heat;  a  heavy  ye'.^ow  gas  is  disengaged,  which  is  th€ 
substance  in  question.     (Fig.  105.) 

It  may  be  collected  over  warm  water,  or  by  displace- 
ment;  the  mercurial  trough  cannot  be  employed,  as 
the  chlorine  rapidly  acts  upon  the  metal,  and  becomes 
absorbed. 


'  From  y\i,n)6i,  yellowish-green,  the  name  given  to  it  by  Sir  H.  DaTy. 


140  CHLORINE. 

The  reaction  is  very  easily  explained.  Hydrochloric  acid  is  a  compound 
of  chlorine  and  hydrogen ;  when  this  is  mixed  with  a  metallic  protoxide, 
double  interchange  of  elements  takes  place,  water  and  chloride  of  the  metal 
being  produced.  But  when  some  of  the  binoxides  are  substituted,  an  addi- 
tional effect  ensues,  namely,  the  decomposition  of  a  second  portion  of  hydro- 
chloric acid  by  the  oxygen  in  excess,  the  hydrogen  of  which  is  withdrawn, 
and  the  chlorine  set  free. 

Hydrochloric     f  Chlorine —Chlorine. 

acid  \  Hydrogen ^____,.-— ^    Water. 


^i°n°n^!nll^     1  Manfa^ese — ^  Chloride  of  manganese. 

manganese      |  Qxygen  ^^ 


Hydrochloric     f  Chlorine 

acid  \  Hydrogen ir===-  Water. 

Chlorine  was  discovered  in  1774,  by  Scheele,  but  its  nature  was  long  mis- 
understood. It  is  a  yellow  gaseous  body,  of  intolerably  suffocating  proper- 
ties, producing  very  violent  cough  and  irritation  when  inhaled  even  in  ex- 
ceedingly small  quantity.  It  is  soluble  to  a  considerable  extent  in  water, 
that  liquid  absorbing  at  60°  (15°-5C)  about  twice  its  volume,  and  acquiring 
the  colour  and  odour  of  the  gas.  When  this  solution  is  exposed  to  light,  it 
IS  slowly  changed  by  decomposition  of  water  into  liydrochloric  acid,  the 
oxygen  being  at  the  same  time  liberated.  When  moist  chlorine  gas  is 
exposed  to  a  cold  of  32°  (0°C),  yellow  crystals  are  formed  which  consist  of 
a  definite  compound  of  chlorine  and  water  containing  35-5  parts  of  the 
former  to  90  of  the  latter. 

Chlorine  has  a  specific  gravity  of  2-47,  100  cubic  inches  weighing  76-6 
grains.  Exposed  to  a  pressure  of  about  four  atmospheres,  it  condenses  to 
a  yellow  limpid  liquid. 

This  substance  has  but  little  attraction  for  oxygen,  its  chemical  energies 
being  principally  exerted  towards  hydrogen  and  the  metals.  When  a  lighted 
taper  is  plunged  into  the  gas,  it  continues  to  burn  with  a  dull  red  light,  and 
emits  a  large  quantity  of  smoke,  the  hydrogen  of  the  wax  being  alone  con- 
sumed, and  the  carbon  separated.  If  a  piece  of  paper  be  wetted  with  oil 
of  turpentine,  and  thrust  into  a  bottle  filled  with  chlorine,  the  chemical 
action  of  the  latter  upon  the  hydrogen  is  so  violent  as  to  cause  inflammation, 
accompanied  by  a  copious  deposit  of  soot.  Although  chlorine  can,  by  indi- 
rect means,  be  made  to  combine  with  carbon,  yet  this  never  occurs  under 
the  circumstances  described. 

Phosphorus  takes  fire  spontaneously  in  chlorine ;  it  burns  with  a  pale  and 
feebly  luminous  flame.  Several  of  the  metals,  as  copper-leaf,  powdered 
antimony,  and  arsenic,  undergo  combustion  in  the  same  manner.  A  mixture 
of  equal  measures  chlorine  and  hydrogen  explodes  with  violence  on  the  pas- 
sage of  an  electric  spark,  or  on  the  application  of  a  lighted  taper,  hydro- 
chloric acid  gas  being  formed.  Such  a  mixture  may  be  retained  in  the  dark 
for  any  length  of  time  without  change ;  exposed  to  diffuse  daylight,  the  two 
gases  slowly  unite,  while  the  direct  rays  of  the  sun  induce  instantaneous 
explosion. 

The  most  characteristic  property  of  chlorine  is  its  bleaching  power;  the 
most  stable  organic  colouring  principles  are  instantly  decomposed  and  de- 
stroyed by  this  remarkable  agent ;  indigo,  for  example,  which  resists  the  ac- 
tion of  strong  oil  of  vitriol,  is  converted  by  chlorine  into  a  brownish  sub- 
stance, to  which  the  blue  colour  cannot  be  restored.  The  presence  of  water 
is  essential  to  these  changes,  for  the  gas  in  a  state  of  perfect  dryness  is  in 
capable  even  of  affecting  litmus. 


CHLORINE, 


141 


Chlorine  is  largely  used  in  the  arts  for  bleaching  linen  and  cotton  goods, 
rags  for  the  manufacture  of  paper,  &c.  For  these  purposes,  it  is  sometimes 
employed  in  the  state  of  gas,  sometimes  in  that  of  solution  in  water,  but 
more  frequently  in  combination  with  lime,  forming  the  substance  called 
bleaching-powder.  When  required  in  large  quantities,  it  is  often  made  by 
pouring  slightly  diluted  oil  of  vitriol  upon  a  mixture  of  common  salt  and 
oxide  of  manganese  contained  in  a  large  leaden  vessel.  The  decomposition 
which  ensues  may  be  thus  represented : — 


Chloride  of 

sodium 
Sulphuric  acid 

Binoxide  of 
manganese 

Sulphuric  acid 


r  Oxygen 

\  Protoxide  of 

(^  manganese 


Chlorine. 
Sulphate  of  soda. 


<  Sulphate  of  man- 
f      ganese 


Chlorine  is  one  of  the  best  and  most  potent  substances  that  can  be  used 
for  the  purpose  of  disinfection,  but  its  employment  requires  care.  Bleach- 
ing-powder mixed  with  water,  and  exposed  to  the  air  in  shallow  vessels,  be- 
comes slowly  decomposed  by  the  carbonic  acid  of  the  atmosphere,  and  the 
chlorine  evolved ;  if  a  more  rapid  disengagement  be  wished,  a  little  acid  of 
any  kind  may  be  added.  In  the  absence  of  bleaching-powder,  either  of  the 
methods  for  the  production  of  the  gas  described  may  be  had  recourse  to, 
always  taking  care  to  avoid  an  excess. 

Chloride  of  Hydrogen  ;  Hydrochloric,  Chlorhydric  or  Muriatic  Acid.  —  This 
substance  in  a  state  of  solution  in  water,  has  been  long  known.  The  gas  is 
prepared  with  the  utmost  ease  by  heating  in  a  flask,  fitted  with  a  cork  and 
bent  tube,  a  mixture  of  common  salt  and  oil  of  vitriol,  diluted  with  a  small 
quantity  of  water ;  it  must  be  collected  by  displacement,  or  over  mercury. 
It  is  a  colourless  gas,  which  fumes  strongly  in  the  air  from  condensing  the 
atmospheric  moisture ;  it  has  an  acid,  suffocating  odour,  but  is  infinitely  less 
offensive  than  chlorine.  Exposed  to  a  pressure  of  40  atmospheres,  it 
liquefies. 

Hydrochloric  acid  gas  has  a  density  1-269.  It  is  exceedingly  soluble  in 
water,  that  liquid  taking  up  at  the  temperature  of  the  air  about  418  timea 
its  bulk.     The  gas  and  solution  are  powerfully  acid. 

The  action  of  oil  of  vitriol  on  common  salt,  or  any  analogous  substance,  if 
thus  easily  explained :  — 


Chloride  of  sodium 


Water 


Sulphuric  acid 


f  Chlorine 
1  Sodium 


Hydrochloric  acid. 


Sulphate  of  soda.. 


The  composition  of  this  substance  may  be  determined  by  synthesis :  when 
a  measure  of  chlorine  and  a  measure  of  hydrogen  are  fired  by  the  electric 
spark,  two  measures  of  hydrochloric  acid  gas  result,  the  combination  being 
unattended  by  change  of  volume.  By  weight  it  contains  35-5  parts  chlorine 
and  1  part  hydrogen. 

Solution  of  hydrochloric  acid,  the  liquid  acid  of  commerce,  is  a  very  im- 
portant preparation,  and  of  extensive  use  in  chemical  pursuits ;  it  is  best 
prepared  by  the  following  arrangement : 

A  large  glass  flask,  containing  a  quantity  of  common  salt,  is  fitted  -with  • 


142 


CHLORINE. 


cork  and  bent  tube,  in  the  manner  represented  in  fig.  106 ;  the  latter  passes 
through  and  below  a  second  short  tube  into  a  wide-necked  bottle,  containing 

Fig.  106 


a  little  "vrater,  into  which  the  open  tube  dips.  A  bent  tube  is  adapted  to  an- 
other hole  in  the  cork  of  the  wash-bottle,  so  as  to  convey  the  purified  gas 
into  a  quantity  of  distilled  water,  by  which  it  is  instantly  absorbed.  The 
joints  are  madie  air-tight  by  melting  over  the  corks  a  little  yellow  wax. 

Oil  of  vitriol,  about  equal  in  weight  to  the  salt,  is  then  slowly  introduced 
by  the  funnel ;  the  disengaged  gas  is  at  first  wholly  absorbed  by  the  water 
in  the  wash-bottle,  but  when  this  becomes  saturated,  it  passes  into  the 
second  vessel  and  there  dissolves.  When  all  the  acid  has  been  added,  heat 
may  be  applied  to  the  flask  by  a  charcoal  chauffer,  until  its  contents  appear 
nearly  dry,  and  the  evolution  of  gas  almost  ceases,  when  the  process  may 
be  stopped.  As  much  heat  is  given  out  during  the  condensation  of  the  gas, 
it  is  necessary  to  surround  the  condensing-vessel  with  cold  water. 

The  simple  wash-bottle  figured  in  the  drawing  will  be  found  an  exceed- 
ingly useful  contrivance  in  a  great  number  of  chemical  operations.  It  serves 
in  the  present,  and  in  many  similar  cases,  to  retain  any  liquid  or  solid  matter 
mechanically  carried  over  with  the  gas,  and  it  may  be  always  employed  when 
gas  of  any  kind  is  to  be  passed  through  an  alkaline  or  other  solution.  The 
open  tube  dipping  into  the  liquid  prevents  the  possibility  of  absorption,  by 
which  a  partial  vacuum  would  be  occasioned,  and  the  liquid  of  the  second 
vessel  iost  by  bein^  driven  into  the  first. 

The  arrangement  by  which  the  acid  is  introduced,  also  deserves  a  moment's 
notice.  The  tube  is  bent  twice  upon  itself,  and  a  bulb  blown  in  one  portion. 
(Fig.  107.)     Liquid  poured  into  the  funnel  rises  upon  the  opposite  side  of 


CHLORINE.  143 

the  first  bend  until  it  reaches  the  second ;  it  then  flows  over  and  runs  into 
the  flask.     Any  quantity  can  then  be  got  into  the  latter  without  the 
introduction  of  air,  and  without  the  escape  of  gas  from  the  inte-    Fig- 107. 
rior.     The  funnel  acts  also  as  a  kind  of  safety-valve,  and  in  both      ^^ 
directions ;  for  if  by  any  chance  the  delivery-tube  should  be  stopped 
and  the  issue  of  gas  prevented,  its  increased  elastic  force  soon  drives 
the  little  column  of  liquid  out  of  the  tube,  the  gas  escapes,  and  the 
vessel  is  saved.    On  the  other  hand,  any  absorption  within  is  quickly 
compensated  by  the  entrance  of  air  through  the  liquid  in  the  bulb. 
The  plan  employed  on  the  great  scale  by  the  manufacturer  is  the 
same  in  principle  as  that  described ;  he  merely  substitutes  a  large 
iron  cylinder  for  the  flask,  and  vessels  of  stone-ware  for  those  of 
glass. 

Pure  solution  of  hydrochloric  acid  is  transparent  and  colourless ; 
when  strong,  it  fumes  in  the  air  by  disengaging  a  little  gas.  It 
leaves  no  residue  on  evaporation,  and  gives  no  precipitate  or  milki- 
ness  with  solution  of  chloride  of  barium.  When  saturated  with  the 
gas,  it  has  a  specific  gravity  of  1'21,  and  contains  about  42  per  cent, 
of  real  acid.  The  commercial  acid  has  usually  a  yellow  colour,  and 
is  very  impure,  containing  salts,  sulphuric  acid,  chloride  of  iron,  and 
organic  matter.  It  may  be  rendered  sufficiently  good  for  most  pur- 
poses by  diluting  it  to  the  density  of  1-1,  which  happens  when  the  strong 
acid  is  mixed  with  its  ovm  bulk  or  rather  less  of  water,  and  then  distilling  it 
in  a  retort  furnished  with  a  Liebig's  condenser. 

A  mixture  of  nitric  and  hydrochloric  acids  has  long  been  known  under  the 
name  of  aqua  regia,  from  its  property  of  dissolving  gold.  When  the^  two 
substances  are  heated  together,  they  both  undergo  decomposition,  hyponitric 
acid  and  chlorine  being  evolved.  This  at  least  appears  to  be  the  final  result 
of  the  action ;  at  a  certain  stage,  however,  two  peculiar  substances,  con- 
sisting of  nitrogen,  oxygen,  and  chlorine,  (chlorohyponitric  acid'  and  chlo- 
ronitrous  acid,'^)  appear  to  be  formed.  It  is  chiefly  the  chlorine  which 
attacks  the  metal. 

The  presence  of  hydrochloric  acid,  or  any  other  soluble  chloride,  is  easily 
detected  by  solution  of  nitrate  of  silver.  A  white  curdy  precipitate  is  pro- 
duced, insoluble  in  nitric  acid,  freely  soluble  in  ammonia,  and  subject  to 
blacken  by  exposure  to  light. 

Compounds  of  Chlorine  and  Oxygen. 
Although  these  bodies  never  combine  directly,  they  may  be  made  to  unite 
by  circuitous  means  in  five  different  proportions,  as  below : — 

Composition  by  weight. 

I ' \ 

Chlorine.        Oxygen. 

Hypochlorous  acid 35-5  8 

Chlorous  acid 35-5  24 

Hypochloric  acid 35-5  32 

Chloric  acid .' 35-5  40 

Perchloric  acid' 35-5  56 

Hypochlorous  and  chloric  acids  are  generated  by  the  action  of  chlorine  on 
certain  metallic  oxides ;  the  former  in  the  cold,  the  latter  at  a  high  tempe 

»  NOa  Ola.  a  NO2CL 

•  Hypochlorons  acid CIO 

Chlorous  acid ClOs 

Hypochloric  acid CIO4 

Chloric  acid ClOs 

Perchloric  acid ■. OIOt 


J44  CHLORINE. 

rature.  Chlorous,  hypoch'oric,  and  perchloric  acids  result  from  the  decom- 
position of  chloric  acids. 

Hypochlorous  Acid.  —  This  is  best  prepared  by  the  action  of  chlorine  gas 
upon  red  oxide  of  mercury.  It  is  a  pale  yellow  gaseous  body,  containing, 
in  every  two  measures,  two  measures  of  chlorine  and  one  of  oxygen.  It  is 
very  freely  soluble  in  water,  and  explodes,  although  with  no  great  violence, 
by  slight  elevation  of  temperature.  The  odour  of  this  gas  is  peculiar,  and 
but  remotely  resembles  that  of  chlorine.  It  bleaches  powerfully,  and  acts 
upon  certain  of  the  metals  in  a  manner  which  is  determined  by  their  re- 
spective attractions  for  oxygen  and  chlorine.  It  forms  with  the  alkalis  a 
series  of  bleaching  salts. 

The  preparations  called  chloride  of,  or  chlorinated  lime  and  soda,  contain 
hypochlorous  acid.  A  description  of  these  will  be  found  under  the  head  of 
Salts  of  Lime. 

The  reaction  by  which  hypochlorous  acid  is  produced  may  thus  be  illus- 
trated :  — 

Chlorine         ___,_,^  Hypochlorous  acid. 

Oxide  of  /  Mercury 
mercury  \  Oxygen 
Chlorine  ■ ^^^=^^~ Chloride  of  mercury. 

The  chloride  of  mercury,  however,  does  not  remain  as  siich ;  it  combines 
with  another  portion  of  the  oxide,  when  the  latter  is  in  excess,  forming  a 
peculiar  brown  compound,  an  oxychloride  of  mercury.' 

Chlorous  Acid.  —  This  substance  is  prepared  by  heating  in  a  flask  filled  to 
I  the  neck,  a  mixture  of  4  parts  of  chlorate  of  potassa  and  3  parts  of  arsenious 
acid  with  12  parts  of  nitric  acid  previously  diluted  by  4  parts  of  water 
During  the  operation,  which  must  be  performed  in  a  water-bath,  a  greenish 
yellow  gas  is  evolved,  which  is  sparingly  soluble  in  water,  and  cannot  be 
condensed  by  exposure  to  a  freezing  mixture.  It  slowly  combines  with 
bases,  producing  a  class  of  salts  called  chlorites.  The  process  which  gives 
rise  to  chlorous  acid  is  rather  complicated.  The  arsenious  acid  deprives  the 
nitric  acid  of  part  of  its  oxygen,  reducing  it  into  nitrous  acid,  which  is 
oxidized  again  at  the  expense  of  the  chloric  acid.  This,  by  the  loss  of  two- 
fifths  of  its  oxygen,  becomes  chlorous  acid. 

Hypochloric  Acid;  Peroxide  of  Chlorine. — Chlorate  of  potassa  is  made  into 
a  paste  with  concentrated  sulphuric  acid,  and  cooled ;  this  is  introduced  into 
a  small  glass  retort,  and  very  cautiously  heated  by  warm  water ;  a  deep 
yellow  gas  is  evolved,  which  is  the  body  in  question ;  it  can  be  collected  only 
by  displacement,  since  mercury  decomposes,  and  water  absorbs  the  gas. 

Hypochloric  acid  has  a  powerful  odour,  quite  different  from  that  of  the 
preceding  compounds,  and  of  chlorine  itself.  It  is  exceedingly  explosive, 
being  resolved  with  violence  into  its  elements  by  a  temperature  short  of  the 
boiling  point  of  water.  Its  preparation  is,  therefore,  always  attended  by 
danger,  and  should  be  performed  only  on  a  small  scale.  It  is  composed 
Dy  measure  of  one  volume  of  chlorine  and  two  volumes  of  oxygen,  con- 

•  A  very  commodious  method  of  preparing  hypochlorous  acid  has  lately  been  described  by 
M.  Pelouze.  Ked  oxide  of  mercury,  prepared  by  precipitation  and  dried  by  exposure  to  a 
Btrong  heat,  is  introduced  into  a  glass  tube,  kept  cool,  and  well  washed,  and  dry  chlorine  gas  is 
Blowly  passed  over  it.  Chloride  of  mercury  and  hypochlorous  acid  are  formed;  the  latter  is 
collected  by  displacement.  When  the  flask  or  bottle  in  which  the  ga»s  is  received  is  exposed 
to  artificial  cold  by  the  aid  of  a  mixture  of  ice  and  salt,  the  hypochlorous  acid  condenses  to  a 
deep  red  liquid,  slowly  soluble  in  water,  and  very  subject  to  explosion.  It  is  remarkable  that 
the  crystalline  oxide  of  mercui-y  prepared  by  calcining  the  nitrate,  or  by  the  direct  oxidation 
of  the  metal,  is  scarcely  aclwl  upon  by  chlorine  under  the  circumstances  described,  —  Ann.. 
Chim.  et  Phys.  3d  series,  viL  179 


CHLORINE. 


145 


Fig.  108. 


iensed  into  two  volumes.*     It  may  be  liquefied  by  cold.    The  solution  of  the 
gas  in  water  bleaches.     Salts  of  this  acid  have  not  yet  been  obtained. 

The  euchlorine  of  Davy,  prepared  by  gently  heating  chlorate  of  potassa 
with  dilute  hydrochloric  acid,  is  probably  a  mixture  of  chlorous  acid  and 
free  chlorine. 

The  production  of  chlorous  acid  from  chlorate  of  potassa  and  sulphuric 
acid,  depends  upon  the  spontaneous  splitting  of  the  chloric  acid  into  chlorous 
acid  and  perchloric  acid,  which  latter  remains  in  union  with  the  potassa.' 

When  a  mixture  of  chlorate  of  potassa  and  sugar  is  touched  with  a  drop 
of  oil  of  vitriol,  it  is  instantly  set  on  fire ;  the  hypochloric  acid  disengaged 
being  decomposed  by  the  combustible  substance  with 
such  violence  as  to  cause  inflammation.  If  crystals 
of  chlorate  of  potassa  be  thrown  into  a  glass  of  water, 
a  few  small  fragments  of  phosphorus  added,  and 
then  oil  of  vitriol  poured  down  a  narrow  funnel 
reaching  to  the  bottom  of  the  glass,  the  phosphorus 
will  burn  beneath  the  surface  of  the  water  by  the  as- 
sistance of  the  oxygen  of  the  hypochloric  acid  disen- 
gaged. Fig.  108.  The  liquid  at  the  same  time 
becomes  yellow,  and  acquires  the  odour  of  that  gas. 

Chloric  Acid.  —  This  is  the  most  important  com- 
pound of  the  series.  When  chlorine  is  passed  to 
saturation  into  a  moderately  strong  hot  solution  of 
caustic  potassa,  or  the  carbonate  of  that  base,  and 
the  liquid  concentrated  by  evaporation,  it  furnishes, 
on  cooling,  flat  tubular  crystals  of  a  colourless  salt, 
consisting  of  potassa  combined  with  chloric  acid. 
The  mother-liquor  contains  chloride  of  potassium.  In  this  reaction  a  part 
of  the  potassa  is  decomposed ;  its  oxygen  combines  with  one  portion  of 
chlorine  to  form  chloric  acid,  while  the  potassium  is  taken  up  by  a  second 
portion  of  the  same  substance.' 

From  chlorate  of  potassa,  chloric  acid  may  be  obtained  by  boiling  the 
salt  with  a  solution  of  hydrofluosilicic  acid,  which  forms  an  almost  insoluble 
salt  with  potassa,  decanting  the  clear  liquid,  and  digesting  it  with  a  little 
silica,  which  removes  the  excess  of  the  hydrofluosilicic  acid.  Filtration 
through  paper  must  be  avoided. 

By  cautious  evaporation,  the  acid  may  be  so  far  concentrated  as  to  assume 
a  syrupy  consistence  ;  it  is  then  very  easily  decomposed.  It  sometimes  sets 
fire  to  paper,  or  other  dry  organic  matter,  in  consequence  of  the  facility  with 
which  it  is  deoxidized  by  combustible  bodies. 

The  chlorates  are  easily  recognized;  they  give  no  precipitate  when  in 
solution  with  nitrate  of  baryta  or  silver;  they  evolve  pure  oxygen  when 
heated,  passing  thereby  into  chlorides ;  and  they  afford,  when  treated  with 
sulphuric  acid,  the  charactei-istic  explosive  yellow  gas  already  described. 
The  dilute  solution  of  the  acid  has  no  bleaching  power. 

Perchloric  Acid. — Prof.  Penny  has  shown  that  when  powdered  chlorate  of 
potassa  is  thrown  by  small  portions  into  hot  nitric  acid,  a,  change  of  the 


*  In  equivalents,  as  already  stated,  CIO4 

•  3  equiv.  chloric  acid 


C  2  eq.  chlorine  ^ -*'  ^ 

<  8  eq.  oxygen  — "^ 

(.  7  eq.  oxygen .. 

1  eq.  chlorine '■ 


6  eq.  chlorine 


5  eq.  chlorine 
1  eq.  chlorine 
r  5  eq.  potassium 
6  eq.  potassa  <  5  eq.  oxygen 

(  1  »q.  potassa ^. 

13 


2  eq.  hypochloric  acjd. 


eq.  perchloric  add. 
--^  0  eq.  chloride  potassium. 

1  eq.  chlorate  pctaasa. 


146 


IODINE. 


same  description  as  that  which  happens  when  sulphuric  acid  is  used  takes 
place,  but  with  this  important  difference,  that  the  chlorine  and  oxygen, 
instead  of  being  evolved  in  a  dangerous  state  of  combination,  are  emitted  in 
a  state  of  mixture.  The  result  of  the  reaction  is  a  mixture  of  nitrate  of 
potassa  and  perchlorate  of  potassa,  which  may  be  readily  separated  by  their 
difference  of  solubility. 

By  treating  the  potassa  salt  in  the  manner  directed  for  chloric  acid,  the 
free  acid  may  be  obtained  tolerably  pure.  It  may  be  concentrated  by  evapo- 
ration, and  even  distilled  without  change.  The  solution  fumes  slightly  in 
the  air,  and  has  a  specific  gravity  of  1-65.  It  is  very  greedy  of  moisture, 
and  has  no  bleaching  properties.  The  perchlorates  much  resemble  the  chlo- 
rates ;  they  give  off  oxygen  when  heated  to  redness.  The  acid  is  the  most 
stable  of  the  compounds  of  chlorine  and  oxygen. 


This  remarkable  substance  was  first  noticed  in  1812  by  M.  Courtois  of 
Paris.  Minute  traces  are  found  in  combination  with  sodium  or  potassium 
in  sea-water,  and  occasionally  a  much  larger  proportion  in  that  of  certain 
mineral  springs.  It  seems  to  be  in  some  way  beneficial  to  many  marine 
plants,  as  these  latter  have  the  power  of  abstracting  it  from  the  surrounding 
water,  and  accumulating  it  in  their  tissues.  It  is  from  this  source  that  all 
the  iodine  of  commerce  is  derived.  It  has  lately  been  found  in  minute 
quantity  in  some  aluminous  slates  of  Sweden,  and  in  several  varieties  of 
coal  and  turf. 

Kelp,  or  the  half-vitrified  ashes  of  sea-weeds,  prepared  by  the  inhabitants 
of  the  Western  Islands  and  the  northern  shores  of  Scotland  and  Ireland,  is 
treated  with  water,  and  the  solution  filtered.  The  liquid  is  then  concentrated 
by  evaporation  until  it  is  reduced  to  a  very  small  volume,  the  chloride  of 
sodium,  carbonate  of  soda,  chloride  of  potassium,  and  other  salts,  being 
removed  as  they  successively  crystallize.  The  dark  brown  mother-liquor 
left  contains  very  nearly  the  whole  of  the  iodine ;  this  is  mixed  with  sul- 
phuric acid  and  binoxide  of  manganese,  and  gently  heated  in  a  leaden  retort, 
when  the  iodine  distils  over  and  condenses  in  the  receiver.  The  theory  of 
the  operation  is  exactly  analogous  to  that  of  the  prepai'ation  of  chlorine; 
it  requires  in  practice,  however,  careful  management,  otherwise  the  impuri- 
ties present  in  the  solution  interfere  with  the  general  result. 

The  manganese  is  not  really  essential ;  iodide  of  potassium  or  sodium, 
heated  with  an  excess  of  sulphuric  acid,  evolves  iodine.  This  effect  is  due 
to  a  secondary  action  between  the  hydriodic-  acid  first  produced,  and  the 
excess  of  the  sulphuric  acid,  in  which  both  suffer  decomposition,  yielding 
iodine,  water,  and  sulphurous  acid. 

Iodine  crystallizes  in  plates  or  scales  of  a  bluish-black  colour  and  imper- 
^ect  metallic  lustre,  resembling  that  of  plumbago ;  the  crystals  are  sometimes 
?ery  large  and  brilliant.  Its  density  is  4-948.  At  225°  (107° -20)  it  fuses, 
and  at  347°  (175°C)  boils,  the  vapour  having  an  exceedingly  beautiful  violet 
colour.'  It  is  slowly  volatile,  however,  at  common  temperatures,  and  exhales 
an  odour  much  resembling  that  of  chlorine.  The  density  of  the  vapour  is 
8*716.  Iodine  requires  for  solution  about  7000  parts  of  water,  which  never- 
theless acquires  a  brown  colour ;  in  alcohol  it  is  much  more  freely  soluble. 
Solutions  of  hydriodic  acid  and  the  iodides  of  the  alkaline  metals  also  dis- 
solve a  large  quantity ;  these  solutions  are  not  decomposed  by  water,  which 
is  the  case  with  the  alcoholic  tincture. 

This  substance  stains  the  skin,  but  not  permanently ;  it  has  a  very  ener- 
getic action  upon  the  animal  system,  and  is  much  used  in  medicine. 

*  Whence  the  name,  to^if  j,  violetswloured. 


IODINE. 


147 


Fig.  109. 


One  of  the  most  characteristic  properties  of  iodine  is  the  production  of  a 
aplendid  blue  colour  by  contact  with  the  organic  principle  starch.  The  iodine 
for  this  purpose  must  be  free  or  uncombined.  It  is  easy,  however,  to  make  tho 
test  available  for  the  purpose  of  recognizing  the  presence  of  the  element  in 
question  when  a  soluble  iodide  is  suspected  ; 
it  is  only  necessary  to  add  a  very  small  quan- 
tity of  chlorine-water,  when  the  iodine,  being 
displaced  from  combination,  becomes  capable 
of  acting  upon  the  starch. 

Ilydriodic  Acid. — The  simplest  process  for 
preparing  hydriodic  acid  gas  is  to  introduce 
into  a  glass  tube  (fig.  109),  sealed  at  one 
extremity,  a  little  iodine,  then  a  small  quan- 
tity of  roughly-powdered  glass  moistened 
with  water,  upon  this  a  few  little  fragments 
of  phosphorus,  and  lastly  more  glass ;  this 
order  of  iodine,  glass,  phosphorus,  glass,  is 
repeated  until  the  tube  is  half  or  two-thirds 
filled.  A  cork  and  narrow  bent  tube  are 
then  fitted,  and  gentle  heat  applied.  The 
gas  is  received  over  mercury.  The  experi- 
ment depends  upon  the  formation  of  an 
iodide  of  phosphorus,  and  its  subsequent 
decomposition  by  water,  hydrated  phospho- 
rous acid  and  iodide  of  hydrogen  being  produced.  The  glass  merely  serves 
to  moderate  the  violence  of  the  action  of  the  iodine  upon  the  phosphorus. 

Hydriodic  acid  gas  greatly  resembles  the  corresponding  chlorine  compound ; 
it  is  colourless,  and  highly  acid ;  it  fumes  in  the  air,  and  is  very  soluble  in 
water.  Its  density  is  about  4-4.  By  weight  it  is  cirtaposed  of  127  parts  iodine 
and  1  part  hydrogen ;  and  by  measure,  of  equal  volumes  of  iodine-vapour 
and  hydrogen  united  without  condensation. 

Solution  of  hydriodic  acid  may  be  prepared  by  a  process  much  less  trou- 
blesome than  the  above.  Iodine  in  fine  powder  is  suspended  in  water,  and 
a  stream  of  washed  sulphuretted  hydrogen  passed  through  the  mixture : 
sulphur  is  deposited,  and  the  iodine  converted  into  hydriodic  acid.  When 
the  liquid  has  become  colourless,  it  is  heated  to  expel  the  excess  of  sulphu- 
retted hydrogen,  and  filtered.  This  solution  cannot  long  be  kept,  especially 
if  it  be  strong ;  the  oxygen  of  the  air  gradually  decomposes  the  hydriodic 
acid,  and  iodine  is  set  free,  which,  dissolving  in  the  remainder,  communicates 
to  it  a  brown  colour. 


Compounds  of  Iodine  and  Oxygen. 
The  most  important  of  these  are  the  iodic  and  periodic  acids. 

Composition  by  weight. 


Iodine. 

Iodic  acid  127 

Periodic  acid  *    127 


Oxygen. 
...  40 
...  56 


Iodic  Acid  may  be  prepared  by  the  direct  oxidation  of  iodine  by  nitric  acia 
of  specific  gravity  1-5;  5  parts  of  dry  iodine  with  200  parts  of  nitric  acid 
are  kept  at  a  boiling  temperature  for  several  hours,  or  until  the  iodine  has 
disappeared.  The  solution  is  then  cautiously  distilled  to  dryness,  and  the 
residue  dissolved  in  water  and  made  to  crystallize. 


lOo,  and  lOt. 


148  BROMINE. 

Iodic  acid  is  a  very  soluble  substance ;  it  crystallizes  in  colourless,  six- 
sided  tables,  which  contain  water.  It  is  decomposed  by  heat,  and  its  solution 
readily  deoxidized  by  sulphurous  acid.  The  iodates  much  resemble  the 
chlorates ;  that  of  potassa  is  decomposed  by  heat  into  iodide  of  potassium 
and  oxygen  gas. 

Periodic  Acid. — When  solution  of  iodate  of  soda  is  mixed  with  caustic 
soda,  and  a  current  of  chlorine  transmitted  through  the  liquid,  two  salts  are 
formed,  namely,  chloride  of  sodium  and  a  combination  of  periodate  of  soda 
with  hydrate  of  soda,  which  is  sparingly  soluble.  This  is  separated,  con- 
verted into  a  silver-salt,  and  dissolved  in  nitric  acid ;  the  solution  yields  on 
evaporation  crystals  of  yellow  periodate  of  silver ;  from  which  the  acid  may 
be  separated  by  the  action  of  water,  which  resolves  the  salt  into  free  acid 
and  insoluble  basic  periodate. 

The  acid  itself  may  be  obtained  in  crystals.  It  is  permanent  in  the  air, 
and  capable  of  being  resolved  into  iodine  and  oxygen  by  a  high  temperature 


Bromine  '  dates  back  to  1826  only,  having  been  discovered  by  M.  Balard  of 
Montpelier.  It  is  found  in  sea- water,  and  is  a  frequent  constituent  of  saline 
springs,  chiefly  as  bromide  of  magnesium  ; — a  celebrated  spring  of  the  kind 
exists  near  Kreuznach  in  Prussia.  Bromine  may  be  obtained  pure  by  the 
following  process,  which  depends  upon  the  fact,  that  ether  agitated  with 
an  aqueous  solution  of  bromine,  removes  the  greater  part  of  that  substance. 

The  mother-liquor,  from  which  the  less  soluble  salts  have  separated  by 
crystallization,  is  exposed  to  a  stream  of  chlorine,  and  then  shaken  up  with 
a  quantity  of  ether;  the  chlorine  decomposes  the  bromide  of  magnesium, 
and  the  ether  dissolves  the  bromine  thus  set  free.  On  standing,  the  ethereal 
solution,  having  a  fine  red  colour,  separates,  and  may  be  removed  by  a  funnel 
or  pipette.  Caustic  potassa  is  then  added  in  excess,  and  heat  applied ; 
bromide  of  potassium  and  bromate  of  potassa  are  formed.  The  solution  is 
evaporated  to  dryness,  and  the  saline  matter,  after  ignition  to  redness  to 
decompose  the  bromate  of  potassa,  heated  in  a  small  retort  with  binoxide 
of  manganese  and  sulphuric  acid  diluted  with  a  little  water,  the  neck  of  the 
retort  being  plunged  into  cold  water.  The  bromine  volatilizes  in  the  form 
of  a  deep  red  vapour,  which  condenses  into  drops  beneath  the  liquid. 

Bromine  is  at  common  temperatures  a  red  thin  liquid  of  an  exceedingly 
intense  colour,  and  very  volatile;  it  freezes  at  about  19°  ( — 7°-2C),  and 
boils  at  145°-4  (63oC).  The  density  of  the  liquid  is  2-976,  and  that  of  the 
vapour  5-39.  The  odour  of  bromine  is  very  suffocating  and  offensive,  much 
resembling  that  of  iodine,  but  more  disagreeable.  It  is  slightly  soluble  in 
water,  more  freely  in  alcohol,  and  most  abundantly  in  ether.  The  aqueous 
solution  bleaches. 

Ifydrobromic  Add. — This  substance  bears  the  closest  resemblance  in  every 
l^articular  to  hydriodic  acid ;  it  has  the  same  constitution  by  volume,  very 
nearly  the  same  properties,  and  may  be  prepared  by  means  exactly  similar, 
substituting  the  one  body  for  the  other.  The  solution  of  hydrobromic  acid 
has  also  the  power  of  dissolving  a  large  quantity  of  bromine,  thereby  acquir- 
ing a  red  tint.  Hydrobromic  acid  contains  by  weight  80  parts  bromine, 
and  1  part  hydrogen. 

Bromic  Add. — Caustic  alkalis  in  presence  of  bromine  undergo  the  same 
change  as  with  chlorine,  bromide  of  the  metal  and  bromate  of  the  oxide 
being  produced ;  these  may  often  be  separated  by  the  inferior  solubility  of 


From  flpwKOf,  a  noisome  smell :  a  very  appropriate  term. 


FLUORINE  —  SILICIUM.  149 

the  latter.  Bromic  acid,  obtained  from  bromate  of  baryta,  closely  resembles 
chloric  acid ;  it  is  easily  decomposed.  The  bromates  when  heated  lose 
oxygen  and  become  bromides. 

No  other  compound  of  bromine  and  oxygen  has  yet  been  described. 


This  element  has  never  been  isolated,  at  least  in  a  state  fit  for  examination ; 
its  properties  are  consequently  in  great  measure  unknown ;  from  the  obser- 
vations made,  it  is  presumed  to  be  gaseous,  and  to  possess  colour,  like 
chlorine.  The  compounds  containing  fluorine  can  be  easily  decomposed,  and 
the  element  transferred  from  one  body  to  another;  but  its  extraordinary 
chemical  energies  towards  the  metals  and  towards  silicium,  a  component  of 
glass,  have  hitherto  baflEled  all  attempts  to  obtain  it  pure  in  a  separate  state. 
As  fluoride  of  calcium  it  exists  in  small  quantities  in  many  animal  substances ; 
such  as  bones.  Several  chemists  have  endeavoured  to  obtain  it  by  decom- 
posing fluoride  of  silver  by  means  of  chlorine  in  vessels  of  fluor-spar,  but 
even  these  experiments  have  not  led  to  a  decisive  result. 

Hydrofluoric  Acid.  — When  powdered  fluoride  of  calcium  (fluor-spar)  is 
heated  with  concentrated  sulphuric  acid  in  a  retort  of  platinum  or  lead  con- 
nected with  a  carefully  cooled  receiver  of  the  same  metal,  a  very  volatile 
colourless  liquid  is  obtained,  which  emits  copious  white  and  highly  suffoca- 
ting fumes  in  the  air.  This  was  formerly  believed  to  be  the  acid  in  an 
anhydrous  state.  M.  Louyet,  however,  states  that  it  still  contains  water, 
and  that  hydrofluoric  acid,  like  hydrochloric  acid,  when  anhydrous,  is  a  gas. 

When  hydrofluoric  acid  is  put  into  water,  it  unites  with  the  latter  with 
great  violence ;  the  dilute  solution  attacks  glass  with  great  facility.  The 
concentrated  acid  dropped  upon  the  skin  occasions  deep  and  malignant  ulcers, 
80  that  great  care  is  requisite  in  its  management.  Hydrofluoric  acid  contains 
19  parts  fluorine  and  1  part  hydrogen. 

In  a  diluted  state,  this  acid  is  occasionally  used  in  the  analysis  of  siliceous 
minerals,  when  alkali  is  to  be  estimated ;  it  is  employed  also  for  etching  on 
glass,  for  which  purpose  the  acid  may  be  prepared  in  vessels  of  lead,  that 
metal  being  but  slowly  attacked  under  these  circumstances.  The  vapour  of 
the  acid  is  also  very  advantageously  applied  to  the  same  object  in  the  fol- 
lowing manner:  the  glass  to  be  engraved  is  coated  with  etching-ground  or 
wax,  and  the  design  traced  in  the  usual  way  with  a  pointed  instrument.  A 
shallow  basin  made  by  beating  up  a  piece  of  sheet  lead  is  then  prepared,  a 
little  powdered  fluor-spar  placed  in  it,  and  enough  sulphuric  acid  added  to 
form  with  the  latter  a  thin  paste.  The  glass  is  placed  upon  the  basin,  with 
the  waxed  side  downwards,  and  gentle  heat  applied  beneath,  which  speedily 
disengages  the  vapour  of  hydrofluoric  acid.  In  a  very  few  minutes  the  ope- 
ration is  complete ;  the  glass  is  then  removed  and  cleaned  by  a  little  warm 
oil  of  turpentine.  When  the  experiment  is  successful,  the  lines  are  very 
:lear  and  smooth. 

No  combination  of  fluorine  and  oxygen  has  yet  been  discovered  i 

4 

SILICIUM. 

Silicium,  sometimes  called  silicon,  in  union  with  oxygen  constituting  silica, 
or  the  earth  of  flints,  is  a  very  abundant  substance,  and  one  of  great  im- 
portance. It  enters  largely  into  the  composition  of  many  of  the  rocks  and  ^^ 
mineral  masses  of  which  the  surface  of  the  earth  is  composed.  The  following 
process  yields  silicium  most  readily.  The  double  fluoride  of  silicium  and 
potassium  is  heated  in  a  glass  tube  with  nearly  its  own  weight  of  metallic 
potassium;  violent  reaction  ensues,  and  silicium  is  set  free.  When  cold, 
tb«  contents  of  the  tube  are  put  into  cold  water,  which  removes  the  salino 
13  ♦ 


1S» 


STLIC'I  UM 


Fig.  110 


matter  and  any  residual  potassium,  and  leaves  untouched  the  silicium.  So 
prepared,  silicium  is  a  dark  brown  powder,  destitute  of  lustre.  Heated  in 
the  air,  it  burns,  and  becomes  superficially  converted  into  silica.  It  is  also 
acted  upon  by  sulphur  and  by  chlorine.  When  silicium  is  strongly  heated  in 
a  covered  crucible,  its  properties  are  greatly  changed ;  it  becomes  darker  in 
colour,  denser,  and  incombustible,  refusing  to  burn  even  when  heated  by  the 
flame  of  the  oxy-hydrogen  blowpipe. 

Silica. — This  is  the  only  known  oxide;  it  contains  21-3  parts  silicium,  and 
24  parts  oxygen.'  Colourless  transparent  rock-crystal  consists  of  silica  very 
nearly  in  a  state  of  purity;  common  quartz,  agate,  calcedony,  flint,  and 
several  other  minerals,  are  also  chiefly  composed  of  this  substance. 

The  experiment  about  to  be  described,  furnishes  silica  in  a  state  of  com- 
plete purity,  and  at  the  same  time  ex- 
hibits one  of  the  most  remarkable  pro- 
perties of  silicium,  namely,  its  attraction 
for  fluorine.  A  mixture  is  made  of  equal 
parts  fluor-spar  and  glass,  both  finely 
powdered,  and  introduced  into  a  glass 
flask,  with  a  quantity  of  oil  of  vitriol.  A 
tolerably  wide  bent  tube,  fitted  to  the 
flask  by  a  cork,  passes  to  the  bottom  of  a 
glass  jar,  into  which  enough  mercury  is 
poured  to  cover  the  extremity  of  the 
tube.  The  jar  is  then  half  filled  with 
water,  and  heat  is  applied  to  the  flask. 
(Fig.  110.) 

The  first  efi'ect  is  the  disengagement 
of  hydrofluoric  acid ;  this  substance,  how- 
ever, finding  itself  in  contact  with  the 
silica  of  the  powdered  glass,  undergoes 
decomposition,  water  and  flouride  of  silicium  being  produced.  The  latter  is 
a  permanent  gas,  which  escapes  from  the  flask  by  the  bent  tube.  By  con- 
tact with  a  large  quantity  of  water,  it  is  in  turn  decomposed,  yielding  silica, 
which  separates  in  a  beautiful  gelatinous  condition,  and  an  acid  liquid  which 
is  a  double  fluoride  of  silicium  and  hydrogen,  commonly  called  hydrofluo- 
silicic  acid.'  The  silica  may  be  collected  on  a  cloth  filter,  well  washed,  dried, 
and  heated  to  redness  to  expel  water. 

The  acid  liquid  is  kept  as  a  test  for  baryta  and  potassa,  with  which  it 
forms  nearly  insoluble  precipitates,  the  double  fluoride  of  silicium  and  potas- 
sium being  used,  as  was  stated,  in  the  preparation  of  silicium.  The  fluoride 
of  silicium,  instead  of  being  conducted  into  water,  may  be  collected  over 
mercury ;  it  is  a  permanent  gas,  destitute  of  colour,  and  very  heavy.  Ad- 
mitted into  the  air,  it  condenses  the  moisture  of  the  latter,  giving  rise  to  a 


»  Or,  SiOa. 

•  (1)  Reaction  of  hydrofluoric  acid  upon  silica: — 
r  Fluorine 


Hydrofluoric  acid 
Silica 


(  Hydrogen    ^ 


f  Silicium 
\  Oxygen 


Gaseous  fluoride  of  silicium. 


Water. 


Fluoride  of  silicium 


2)  Decomposition  of  fluoride  of  silicium  by  water 

Silicium    ^:::=»  Silica 

Fluoriae 

Wfttflr  -!  Oxygen 

^^^"^  t  Hydrogen 

Fluoride  of  silicium 


Hydr©fluoBllicic  acid. 


BORON. 


151 


thick  white  cloud.  It  is  important  in  the  experiment  above  described  to 
keep  the  end  of  the  delivery-tube  from  touching  the  water  of  the  jar,  other- 
wise it  almost  instantly  becomes  stopped ;  the  mercury  effects  this  object. 

There  is  another  method  by  which  pure  silica  can  be  prepared,  and  which 
is  also  very  instructive,  inasmuch  as  it  is  the  basis  of  the  proceeding  adopted 
in  the  analysis  of  all  siliceous  minerals.  Powdered  rock-crystal  or  fine  sand 
is  mixed  with  about  three  times  its  weight  of  dry  carbonate  of  soda,  and  the 
mixture  fused  in  a  platinum  crucible.  When  cold,  the  glassy  mass  is  boiled 
with  water,  by  which  it  is  softened,  and  almost  entirely  dissolved.  An  excess 
of  hydrochloric  acid  is  then  added  to  the  filtered  liquid,  and  the  whole  eva- 
porated to  complete  dryness.  By  this  treatment  the  gelatinous  silica  thrown 
down  by  the  acid  becomes  completely  insoluble,  and  remains  behind  when 
the  dry  saline  mass  is  treated  with  acidulated  water,  by  which  the  alkaline 
salts,  alumina,  sesquioxide  of  iron,  lime,  and  many  other  bodies  which  may 
happen  to  be  present,  are  removed.  The  silica  is  washed,^  dried,  and  heated 
red-hot. 

The  most  prominent  characters  of  silica  are  the  following :  it  is  a  very 
fine,  white,  tasteless  powder,  not  sensibly  soluble  in  water  or  dilute  acids 
(with  the  exception  of  hydrofluoric)  unless  recently  precipitated.  It  dis- 
solves, on  the  contrary,  freely  in  strong  alkaline  solutions.  Its  density  is 
about  2-66,  and  it  is  only  to  be  fused  by  the  oxy-hydrogen  blowpipe. 

Silica  is  in  reality  an  acid,  and  a  very  powerful  one  ;  insolubility  in  water 
prevents  the  manifestation  of  acid  properties  under  ordinary  circumstances. 
When  heated  with  bases,  especially  those  which  are  capable  of  undergoing 
fusion,  it  unites  with  them  and  forms  true  salts,  which  are  sometimes  solu- 
ble in  water,  as  in  the  case  of  the  silicates  of  potassa  and  soda  when  the 
proportion  of  base  is  considerable.  Common  glass  is  a  mixture  of  several 
silicates  in  which  the  reverse  of  this  happens,  the  silica,  or  as  it  is  more  cor- 
rectly called,  silicic  acid,  being  in  excess.  Even  glass,  however,  is  slowly 
acted  upon  by  water. 

Finely-divided  silica  is  highly  useful  in  the  manufacture  of  porcelain. 


This  substance  is  closely  related  to  silicium ;  it  is  the  basis  of  boracic 
acid. 

Boron  is  prepai'ed  by  a  process  very  similar  to  that  described  in  the  case 
of  silicium,  the  double  fluoride  of  boron  and  potassium  being  substituted  for 
the  other  salt,  and  the  operation  conducted  in  a  small  iron  vessel  instead  of 
a  glass  tube.  It  is  a  dull  greeuish-brown  powder,  which  bums  in  the  air 
when  heated,  producing  boracic  acid.  Nitric  acid,  alkalis  in  a  fused  condi- 
tion, chlorine,  and  other  agents,  attack  it  readily. 

There  is  but  one  oxide  of  boron,  namely,  boracic  acid,  containing  109  parts 
boron  and  24  parts  oxygen.' 

Boracic  acid  is  found  in  solution  in  the  water  of  the  hot  volcanic  lagoons 
of  Tuscany,  whence  a  large  supply  is  at  pi-esent  derived.  It  is  also  easily 
made  by  decomposing  with  sulphuric  acid  a  hot  solution  of  borax,  a  salt 
brought  from  the  East  Indies,  consisting  of  boracic  acid  combined  with  soda. 

Boracic  acid  crystallizes  in  transparent  colourless  plates,  soluble  in.  about 
25  parts  of  cold  water,  and  in  a  much  smaller  quantity  at  a  boiling  heat ; 
the  acid  has  but  little  taste,  and  feebly  affects  vegetable  colours.  When 
heated,  it  loses  water,  and  melts  to  a  glassy  transparent  mass,  which  dis- 
solves many  metallic  oxides  with  great  ease.  The  crystals  contain  34-9 
parts  real  acid,  and  27  parts  water.  They  dissolve  in  alcohol,  and  the  solu- 
tion burns  with  a  green  flame. 

»BOs. 


152  ^  BORON. 

Glassy  boracic  acid  in  a  state  of  fusion  requires  for  its  dissipation  in 
vapour  a  yery  intense  and  long-continued  heat ;  the  solution  in  water  cannot, 
however,  be  evaporated  without  very  appreciable  loss  by  volatilization ; 
hence  it  is  probable  that  the  hydrate  is  far  more  volatile  than  the  acid  itself. 

By  heating  in  a  glass  flask  or  retort  one  part  of  the  vitrified  boracic  acid, 
2  of  fluor-spar,  and  12  of  oil  of  vitriol,  a  gaseous  fluoride  of  boron  may  be 
obtained,  and  received  in  glass  jars  standing  over  mercury.  It  is  a  trans- 
parent gas,  very  soluble  in  water,  and  very  heavy ;  it  forms  a  dense  fume  in 
the  air  like  the  fluoride  of  silicium.' 

*  These  two  bodies  are  thus  constituted :  —  SiFs,  and  BF». 


COMPOUNDS    OP    CARBON    AND    HYDftOGEN.         153 


ON  CEETAIN  IMPORTANT  COMPOUNDS  FORMED  BY  THE  UNION  OF 
THE  PRECEDING  ELEMENTS  AMONG  THEMSELVES. 


COMPOUNDS  OF  GABBON  AI7D  HYDBOGEN. 

The  compounds  of  carbon  and  hydrogen  already  known  are  exceedingly 
numerous ;  perhaps  all,  in  strictness,  belong  to  the  domain  of  organic  che- 
mistry, as  they  cannot  be  formed  by  the  direct  union  of  their  elements,  but 
always  arise  from  the  decomposition  of  a  complex  body  of  organic  origin. 
It  will  be  found  convenient,  notwithstanding,  to  describe  two  of  them  in  this 
part  of  the  volume,  as  they  very  well  illustrate  the  important  subjects  of 
combustion,  and  the  nature  of  flame. 

Light  Carbonetted  or  Carburetted  Hydrogen  ;  Marsh-gas  ;  Fire-damp  ;  Gas  of 
the  Acetates. — This  gas  is  but  too  often  found  to  be  abundantly  disengaged  in 
coal-mines  from  the  fresh-cut  surface  of  the  coal,  and  from  remarkable  aper- 
tures or  "  blowers,"  which  emit  for  a  great  length  of  time  a  copious  stream 
or  jet  of  gas,  which  probably  existed  in  a  state  of  compression,  pent  up  in 
the  coal. 

The  mud  at  the  bottom  of  pools  in  which  water-plants  grow,  on  being 
stirred,  sufi'ers  bubbles  of  gas  to  escape,  which  may  be  easily  collected. 
This,  on  examination,  is  found  to  be  chiefly  a  mixture  of  light  carbonetted 
hydrogen  and  carbonic  acid ;  the  latter  is  easily  absorbed  by  lime-water  or 
caustic  potassa. 

Until  recently,  no  method  was  known  by  which  the  gas  in  question  could 
be  produced  in  a  state  approaching  to  purity  by  artificial  means  ;  the  various 
illuminating  gases  from  pit-coal  and  oil,  and  that  obtained  by  passing  the 
vapour  of  alcohol  through  a  red-hot  tube,  contain  large  quantities  of  light 
carbonetted  hydrogen,  associated,  however,  with  other  substances  which 
hardly  admit  of  separation,  M.  Dumas  was  so  fortunate  as  to  discover  a 
method  by  which  that  gas  can  be  produced  at  will,  perfectly  pure,  and  in 
any  quantity. 

A  mixture  is  made  of  40  parts  crystallized  acetate  of  soda,  40  parts  solid 
hydrate  of  potassa,  and  60  parts  quicklime  in  powder.  This  mixture  is 
transferred  to  a  flask  or  retort,  and  strongly  heated ;  the  gas  is  disengaged 
in  great  abundance,  and  may  be  received  over  water.' 

Light  carbonetted  hydrogen  is  a  colourless  and  nearly  inodorous  gas,  which 
does  not  affect  vegetable  colours.     It  burns  with  a  yellow  flame,  generating 

»  Ann.  Chim.  et  Phys.  Ixxjii.  93.  The  reaction  consists  in  the  conversion  of  the  acetic  acid, 
by  the  aid  of  the  elements  of  water,  into  ■carbonic  acid  and  light  carbonetted  hydrogen;  the 
instability  of  the  organic  acid  at  a  high  temperature,  and  the  attraction  of  the  potassa  for 
carbonic  acid,  being  the  determining  causes.  The  lime  prevents  the  hydrate  of  potasaa  from 
fusing  and  attacking  the  glass  vessels.  This  decomposition  is  best  understood  by  putting  it 
In  the  shape  of  an  equation. 

Acetic  acid  C4H3O3  "I  ^  f  Carbonic  acid,  2  eq.  C2     O4. 
Water  H  0  J       ( Marsh-gas,  2  eq.       CaH4 

C4H404.  €411404. 


154  coMPOUNDSor 

carbonic  acid  and  water.  It  is  not  poisonous,  and  may  be  respired  to  a  great 
extent  without  apparent  injury.  The  density  of  this  compound  is  about 
0-559,  100  cubic  inches  weighing  17-41  grains;  and  it  contains  carbon  and 
hydrogen  associated  in  the  proportion  of  6  parts  by  weight  of  the  former  to 
2  of  the  latter.' 

When  100  measures  of  this  gas  are  mixed  with  200  of  pure  oxygen  in  the 
eudiometer,  and  the  mixture  exploded  by  the  electric  spark,  100  measures 
of  a  gas  remain  wh  ch  is  entirely  absorbable  by  a  little  solution  of  caustic 
potassa.  Now  carbonic  acid  contains  its  own  volume  of  oxygen ;  hence  one- 
half  of  the  oxygen  added,  that  is,  100  measures,  must  have  been  consumed 
in  uniting  with  the  hydrogen.  Consequently,  the  gas  must  contain  twice  its 
own  measure  of  hydrogen,  and  enough  carbon  to  produce,  when  completely 
burned,  an  equal  quantity  of  carbonic  acid. 

When  chlorine  is  mixed  with  light  carbonetted  hydrogen  over  water,  no 
change  follows,  provided  light  be  excluded.  The  presence  of  light,  however, 
brings  about  decomposition,  hydrochloric  acid,  carbonic  acid,  and  sometimes 
other  products  being  produced.  It  is  important  to  remember  that  the  gas 
is  not  acted  upon  by  chlorine  in  the  dark. 

Olefiant  Gas.  —  Strong  spirit  of  wine  is  mixed  with  five  or  six  times  its 
weight  of  oil  of  vitriol  in  a  glass-flask,  the  tube  of  which  passes  into  a  wash- 
bottle  containing  caustic  potassa.  A  second  wash-bottle,  partly  filled  with 
oil  of  vitriol,  is  connected  to  the  first,  and  furnished  with  a  tube  dipping  into 
the  water  of  the  pneumatic  trough.  On  the  first  application  of  heat  to  the 
contents  of  the  flask,  alcohol,  and  afterwards  ether,  make  their  appearance ; 
but,  as  the  temperature  rises,  and  the  mixture  blackens,  the  ether-vapour 
diminishes  in  quantity,  and  its  place  becomes  in  great  part  supplied  by  a 
permanent  inflammable  gas ;  carbonic  acid  and  sulphurous  acid  are  also 
generated  at  the  same  time,  besides  traces  of  other  products.  The  two  last- 
mentioned  gases  are  absorbed  by  the  alkali  in  the  first  bottle,  and  the  ether 
vapour  by  the  acid  in  the  second,  so  that  the  olefiant  gas  is  delivered  tole- 
rably pure.  The  reaction  is  too  complex  to  be  discussed  at  the  present  mo- 
ment ;  it  will  be  found  fully  described  in  another  part  of  the  volume.  Ole- 
fiant gas  thus  produced  is  colourless,  neutral,  and  but  slightly  soluble  in 
water.  Alcohol,  ether,  oil  of  turpentine,  and  even  olive  oil,  as  Mr.  Faraday 
has  observed,  dissolve  it  to  a  considerable  extent.'^  It  has  a  faint  odour  o^ 
garlic.  On  the  approach  of  a  kindled  taper  it  takes  fire,  and  burns  with  a 
splendid  white  light,  far  surpassing  in  brilliancy  that  produced  by  light  car- 
bonetted hydrogen.  This  gas,  when  mixed  with  oxygen  and  fired,  explodes 
with  extreme  violence.  Its  density  is  0-981 ;  100  cubic  inches  weigh  30-57 
grains. 

By  the  use  of  the  eudiometer,  as  already  described,  it  has  been  found  that 
each  measure  of  olefiant  gas  requires  for  complete  combustion  exactly  three 
of  oxygen,  and  produces  under  these  circumstances  two  measures  of  car- 
bonic acid.  Whence  it  is  evident  that  it  contains  twice  its  own  volume  of 
hydrogen,  combined  with  twice  as  much  carbon  as  in  marsh-gas. 

By  weight,  these  proportions  will  be  12  parts  carbon,  and  2  parts 
hydrogen. 

Olefiant  gas  is  decomposed  by  passing  through  a  tube  heated  to  bright 
redness ;  a  deposit  of  charcoal  takes  place,  and  the  gas  becomes  converted 

»  The  two  carbides  of  hydrogen  here  described  are  thus  represented  in  equivalents: — 
Light  carbonetted  hydrogen    C  Ila 

Olefiant  gas C2II3 

'■'  Olefiant  gas,  by  pressure  and  intense  cold,  produced  by  the  evaporation  in  a  vacuum  of 
solid  carbonic  acid  and  ether,  is  condensed  into  a  colourless  transparent  liquid,  but  not  frozen, 
flaraday.)— R  B. 


CARBON    AND     HYDROGEN.  155 

into  light  carbonetted  hydrogen,  or  even  into  free  hydrogen,  if  the  temper- 
ature be  very  high.  This  latter  change  is  of  course  attended  by  increase  of 
volume. 

Chlorine  acts  upon  defiant  gas  in  a  very  remarkable  manner.  When  the 
two  bodies  ai*e  mixed,  even  in  the  dark,  they  combine  in  equal  measures,  and 
give  rise  to  a  heavy  oily  liquid,  of  sweetish  taste  and  ethereal  odour,  to 
which  the  name  chloride  of  hydrocarbon,  or  Dutch  liquid,  is  given.  It  is 
from  this  peculiarity  that  the  term  olefiant  is  derived. 

A  pleasing  and  instructive  experiment  may  also  be  made  by  mixing  in  a 
tall  jar  two  measures  of  chlorine  and  one  of  olefiant  gas,  and  then  quickly 
applying  a  light  to  the  mouth  of  the  vessel.  The  chlorine  and  hydrogen 
unite  with  flame,  which  passes  quickly  down  the  jar,  while  the  whole  of  the 
carbon  is  set  free  in  the  form  of  a  thick  black  smoke. 

Coal  ajid  Oil  Gases. — The  manufacture  of  coal-gas  is  at  the  present  mo- 
ment a  branch  of  industry  of  great  interest  and  importance  in  several 
points  of  view.  The  process  is  one  of  great  simplicity  of  principle,  but 
requires,  in  practice,  some  delicacy  of  management  to  yield  a  good  result. 

When  pit-coal  is  subjected  to  destructive  distillation,  a  variety  of  products 
show  themselves ;  permanent  gases,  steam,  and  volatile  oils,  besides  a  not 
inconsiderable  quantity  of  ammonia  from  the  nitrogen  always  present  in  the 
coal.  These  substances  vary  very  much  in  their  proportions  with  the  tem- 
perature at  which  the  process  is  conducted,  the  permanent  gases  becoming 
more  abundant  with  increased  heat,  but  at  the  same  time  losing  much  of 
their  value  for  the  purposes  of  illumination. 

The  coal  is  distilled  in  cast-iron  retorts,  maintained  at  a  bright  red  heat, 
and  the  volatilized  products  conducted  into  a  long  horizontal  pipe  of  large 
dimensions,  always  half  filled  with  liquid,  into  which  dips  the  extremity  of 
each  separate  tube  ;  this  is  called  the  hydraulic  main.  The  gas  and  its  ac- 
companying vapours  are  next  made  to  traverse  a  refrigerator,  usually  a 
series  of  iron  pipes,  cooled  on  the  outside  by  a  stream  of  water ;  here  the 
condensation  of  the  tar  and  ammoniacal  liquid  becomes  complete,  and  the 
gas  proceeds  onwards  to  another  part  of  the  apparatus,  in  which  it  is  to  be 
deprived  of  the  sulphuretted  hydrogen  and  carbonic  acid  gases  always  present 
in  the  crude  product.  This  is  generally  effected  by  hydrate  of  lime,  which 
readily  absorbs  the  compounds  in  question.  The  purifiers  are  large  iron 
vessels,  partly  filled  with  a  mixture  of  hydrate  of  lime. and  water,  in  which 
a  churning  machine  or  agitator  is  kept  in  constant  motion  to  prevent  the 
subsidence  of  the  lime.  The  gas  is  admitted  at  the  bottom  of  the  vessel  by 
a  great  number  of  minute  apertures,  and  is  thus  made  to  present  a  large 
surface  of  contact  to  the  purifying  liquid.  The  last  part  of  the  operation, 
which  indeed  is  often  omitted,  consists  in  passing  the  gas  through  dilute 
sulphuric  acid,  in  order  to  remove  ammonia.  The  quantity  thus  separated 
is  very  small,  relatively  to  the  bulk  of  the  gas,  but  in  an  extensive  work  be- 
comes an  object  of  importance. 

Coal-gas  thus  manufactured  and  purified  is  preserved  for  use  in  immense 
cylindrical  receivers,  close  at  the  top,  suspended  in  tanks  of  water  by  chains 
to  which  counterpoises  are  attached,  so  that  the  gas-holders  rise  and  sink 
in  the  liquid  as  they  become  filled  from  the  purifiers  or  emptied  by  the  mains. 
These  latter  are  made  of  large  diameter,  to  diminish  as  much  as  possible  the 
resistance  experienced  by  the  gas  in  passing  through  such  a  length  of  pipe. 
The  joints  of  these  mains  are  yet  made  in  such  an  imperfect  manner,  that 
immense  loss  is  experienced  by  leakage  when  the  pressure  upon  the  gas  at 
the  works  exceeds  that  exerted  by  a  column  of  water  an  inch  in  height.^ 

'It  may  give  some  idea  of  the  extent  of  this  species  of  manufacture,  to  mention,  that  in- 
its  year  18-38,  for  lighting  London  and  the  suburbs  alone,  there  were  eighteen  public  gas 
worky,  and  £2,SOO,000  invested  in  pipes  and  apparatus.    The  yearly  revenue  amounted  tc 


156  COMBUSTION,     AND 

Coal-gas  varies  much  in  composition,  judging  from  its  variable  density 
and  illuminating  power,  and  from  the  analyses  which  have  been  made.  The 
difficulties  of  such  investigations  are  very  great,  and  unless  particular  pre- 
caution be  taken,  the  results  are  merely  approximative.  The  purified  gas  is 
believed  to  contain  the  following  substances,  of  which  the  first  is  most  abun- 
dant, and  the  second  most  valuable. 

Light  carbonetted  hydrogen. 

defiant  gas. 

Hydrogen. 

Carbonic  oxide. 

Nitrogen. 

Vapours  of  volatile  liquid  carbides  of  hydrogen.* 

Vapour  of  bisulphide  of  carbon. 

Separated  by  Condensation  and  by  the  Purifiers. 

Tar  and  volatile  oils. 

Sulphate  of  ammonia,  chloride  and  sulphide  of  ammonium. 

Sulphuretted  hydrogen. 

Carbonic  acid. 

Hydrocyanic  acid,  or  cyanide  of  ammonium. 

A  very  far  better  illuminating  gas  may  be  prepared  from  oil,  by  dropping 
it  into  a  red-hot  iron  retort  filled  with  coke ;  the  liquid  is  in  great  part  de- 
composed and  converted  into  permanent  gas,  which  requires  no  purification, 
as  it  is  quite  free  from  the  ammoniacal  and  sulphur  compounds  which  vitiate 
the  gas  from  coal.  A  few  years  ago  this  article  was  prepared  in  London  ;  it 
was  compressed  for  the  use  of  the  consumer  into  strong  iron  vessels,  to  the 
extent  of  30  atmospheres  ;  these  were  furnished  with  a  screw-valve  of  pecu- 
liar construction,  and  exchanged  for  others  when  exhausted.  The  comparative 
high  price  of  the  material,  and  other  circumstances,  led  to  the  abandonment 
of  the  undertaking. 

COMBUSTION,    AND    THE    STRUCTURE    OF   FLAME. 

When  any  solid  substance,  capable  of  bearing  the  fire,  is  heated  to  a  certain 
point,  it  emits  light,  the  character  of  which  depends  upon  the  temperature. 
Thus,  a  bar  of  platinum  or  a  piece  of  porcelain  raised  to  a  particular  tempe- 
rature, become  what  is  called  red-hot,  or  emissive  of  red  light ;  at  a  higher 
degree  of  heat  this  light  becomes  whiter  and  more  intense,  and  when  urged 
to  the  utmost,  as  in  the  case  of  a  piece  of  lime  placed  in  the  flame  of  the  oxy- 
hydrogen  blowpipe,  the  light  becomes  exceedingly  powerful  and  acquires  a 
tint  of  violet.     Bodies  in  these  states  are  said  to  be  incandescent  or  ignited. 

Again,  if  the  same  experiment  be  made  on  a  piece  of  charcoal,  similar 
effects  will  be  observed,  but  something  in  addition ;  for  whereas  the  platinum 
or  porcelain,  when  removed  from  the  fire,  or  the  lime  from  the  blow-pipe 
flame,  begin  immediately  to  cool,  and  emit  less  and  less  light,  until  they 
become  completely  obscure,  the  charcoal  maintains  to  a  great  extent  its  high 
temperature.  Unlike  the  other  bodies  too,,  which  suffer  no  change  whatever 
either  of  weight  or  substance,  the  charcoal  gradually  wastes  away  until  it 

£450,000,  and  the  consumption  of  coal  in  the  same  period  to  180,000  tons,  1,460  millions  of 
cubic  feet  of  gas  being  made  in  the  year.  There  were  134,300  private  lights,  and  30,400  street 
lamps.  890  tons  of  coal  were  used  in  the  retorts  in  the  space  of  twenty-four  hours  at  mid- 
winter, and  7,120,000  cubic  feet  of  gas  consumed  in  the  longest  night. —  Dr.  Ure,  Dictionary 
of  Arts  and  Manufactures.  Since  that  time  the  production  of  gas  has  been  very  considerably 
Increased. 

'  These  bodies  increasA  th<>  illuminatius  power,  and  confer  on  th«  gas  its  peculiar  odour. 


THE    STRUCTURE    OF    FLAME. 


157 


disappears.  This  is  what  is  called  combustion  in  contradistinction  to  mere 
ignition ;  the  charcoal  burns,  and  its  temperature  is  kept  up  by  the  heat 
evolved  in  the  act  of  union  with  the  oxygen  of  the  air. 

In  the  most  general  sense,  a  body  in  a  state  of  combustion  is  one  in  the 
act  of  undergoing  intense  chemical  action :  any  chemical  action  whatsoever, 
if  its  energy  rise  sufficiently  high,  may  produce  the  phenomenon  of  com- 
bustion, by  heating  the  body  to  such  an  extent  that  it  becomes  luminous. 

In  all  ordinary  cases  of  combustion,  the  action  lies  between  the  burning 
body  and  the  oxygen  of  the  air ;  and  since  the  materials  employed  for  the 
economical  production  of  heat  and  light  consist  of  carbon  chiefly,  or  that 
substance  conjoined  with  a  certain  proportion  of  hydrogen  and  oxygen,  all 
common  effects  of  this  nature  are  cases  of  the  rapid  and  violent  oxidation 
of  carbon  and  hydrogen  by  the  aid  of  the  free  oxygen  of  the  air.  The  heat 
must  be  referred  to  the  act  of  chemical  union,  and  the  light  to  the  elevated 
temperature. 

By  this  principle  it  is  easy  to  understand  the  means  which  must  be  adopted 
to  increase  the  heat  of  ordinary  fires  to  the  point  necessary  to  melt  refrac- 
tory metals,  and  to  bring  about  certain  desired  eflFects  of  chemical  decom- 
position. If  the  rate  of  consumption  of  the  fuel  can  be  increased  by  a  more 
rapid  introduction  of  air  into  the  burning  mass,  the  intensity  of  the  heat 
will  of  necessity  rise  in  the  same  ratio,  there  being  reason  to  believe  that  the 
quantity  of  heat  evolved  is  fixed  and  definite  for  the  same  constant  quantity 
of  chemical  action.  This  increased  supply  of  air  may  be  efi'ected  by  two 
distinct  methods ;  it  may  be  forced  into  the  fire  by  bellows  or  blowing- 
machinesj  as  in  the  common  forge,  and  in  the  blast  and  cupola-furnaces  of 
the  iron-worker,  or  it  may  be  drawn  through  the  burning  materials  by  the 
help  of  a  tall  chimney,  the  fire-place  being  closed  on  all  sides,  and  no  en- 
trance of  air  allowed,  save  between  the  bars  of  the  grate.  Such  is  the  kind 
of  furnace  generally  employed  by  the  scientific  chemist  in  assaying  and  in 
the  reduction  of  metallic  oxides  by  charcoal ;  the  principle  will  be  at  once 
understood  by  the  aid  of  the  sectional  drawing,  in  which  a  crucible  is  repre- 
sented, arranged  in  the  fire  for  an  operation  of  the  kind  mentioned. 
(Fig.  HI.) 

Fig.  111.  Fig.  112 


^_j| 


158  COMBUSTION,    AND 

The  "  reverberatory"  furnace  (fig.  112)  is  one  very  much  used  in  the  arts 
when  substances  are  to  be  exposed  to  heat  without  contact  with  the  fuel. 
The  fire-chamber  is  separated  from  tlie  bed  or  hearth  of  the  furnace  by  a 
low  wall  or  bridge  of  brick-work,  and  the  flame  and  heated  air  are  reflected 
downwards  by  the  arched  form  of  the  roof.  Any  degree  of  heat  can  be  ob- 
tained in  a  furnace  of  this  kind,  from  the  temperature  of  dull  redness,  to 
that  required  to  melt  very  large  quantities  of  cast-iron.  The  fire  is  urged 
by  a  chimney  provided  with  a  sliding-plate  or  damper  to  regulate  the  draught. 
Solids  and  liquids,  as  melted  metal,  enjoy,  when  sufficiently  heated,  the 
faculty  of  emitting  light;  the  same  power  is  possessed  by  gaseous  bodies, 
but  the  temperature  required  to  render  a  gas  luminous  is  incomparably 
higher  than  in  the  cases  already  described.  Gas  or  vapour  in  this  condition 
constitutes  flame,  the  actual  temperature  of  which  generally  exceeds  that  of 
the  white  heat  of  solid  bodies. 

The  light  emitted  from  pure  flame  is  exceedingly  feeble ;  illuminating 
power  is  almost  entirely  dependent  upon  the  presence  of  solid  matter.  The 
flame  of  hydrogen,  or  of  the  mixed  gases,  is  scarcely  visible  in  full  daylight ; 
in  a  dusty  atmosphere,  however,  it  becomes  much  more  luminous  by  igniting 
to  intense  whiteness  the  floating  particles  with  which  it  comes  in  contact.  The 
piece  of  lime  in  the  blowpipe  flame  cannot  have  a  higher  temperature  than 
that  of  the  flame  itself;  yet  the  light  it  throws  oif  is  infinitely  greater. 

Flames  burning  in  the  air,  and  not  supplied  with  oxygen 
Fig.  113.  from  another  source,  are,  as  already  stated,  hollow ;  the  che- 

mical action  is  necessarily  confined  to  the  spot  where  the  two 
/\  bodies  unite.     That  of  a  lamp  or  candle,  when  carefully  ex- 

/A----C        amined,  is  seen  to  consist  of  three  separate  portions.     The 
//\\  dark  central  part,  a,  fig.  113,  easily  rendered  evident  by  de- 

//  -\-\ --— B       pressing  upon  the  flame  a  piece  of  fine  wire-gauze,  consists  of 
(/  A  u  combustible  matter  drawn  up  by  the  capillarity  of  the  wick, 

ll  /  Vj'""-^      ^^^  volatilized  by  the  heat.     This  is  surrounded  by  a  highly 
\\\    \jj  luminous  cone  or  envelope,  b,  which,  in  contact  with  a  cold 

m  hody,  deposits  soot.     On  the  outside  a  second  cone,  c,  is  to 

r-ft-j  be  traced,  feeble  in  its   light-giving  power,  but  having  an 

UaJ  exceedingly  high  temperature.    The  explanation  of  these  ap- 

pearances is  easy :  carbon  and  hydrogen  are  very  unequal  in 
their  attraction  for  oxygen,  the  latter  greatly  exceeding  the  former  in  this 
respect ;  consequently,  when  both  are  present,  and  the  supply  of  oxygen 
limited,  the  hydrogen  takes  all,  to  the  exclusion  of  a  great  part  of  the  car- 
bon. Now  this  happens  in  the  case  under  consideration,  at  some  little  dis- 
tance within  the  outer  surface  of  the  flame,  namely,  in  the  luminous  portion  ; 
the  little  oxygen  which  has  penetrated  thus  far  inwards  is  entirely  consumed 
by  the  hydrogen,  and  the  particles  of  deposited  charcoal,  which  would,  were 
they  cooler,  form  smoke,  become  intensely  ignited  by  the  burning  hydrogen, 
and  evolve  a  light  whose  whiteness  marks  a  very  elevated  temperature.  In 
the  exterior  and  scarcely  visible  cone,  these  particles  of  carbon  undergo 
combustion. 

A  jet  of  coal-gas  exhibits  these  phenomena;  but,  if  the  gas  be  previously 
mingled  with  air,  or  if  air  be  forcibly  mixed  with,  or  driven  into  the  flame, 
no  such  separation  of  carbon  occurs,  the  hydrogen  and  carbon  burn  together, 
and  the  illuminating  power  almost  disappears. 

The  common  mouth  blowpipe  is  a  little  instrument  of  high  utility ;  it  is 
merely  a  brass  tube,  fitted  with  an  ivory  mouth-piece,  and  terminated  by  a 
jet,  having  a  small  aperture  by  which  a  current  of  air  is  driven  across  the 
flame  of  a  candle.  The  best  form  is  perhaps  that  contrived  by  Mr.  Pepys, 
and  shown  in  fig.  114.     The  flame  so  produced  is  very  peculiar. 

Instead  of  the  double  envelope  just  described,  two  long  pointed  cones  are 


THE    STRUCTURE    OF    PLAMB. 


159 


observed,  which,  when  the  blowpipe  is  good,  and 
the  aperture  smooth  and  round,  are  very  well  de- 
fined, the  outer  one  being  yellowish,  and  the  inner 
blue.  Fig.  115.  A  double  combustion  is,  in  fact, 
going  on,  by  the  blast  in  the  inside,  and  by  the 
external  air.  The  space  between  the  inner  and 
outer  cones  is  filled  with  exceedingly  hot  com- 
bustible matter,  possessing  strong  reducing  or 
deoxidizing  powers,  while  the  highly  heated  air 
just  beyond  the  point  of  the  exterior  cone  ox- 
idizes with  great  facility.  A  small  portion  of 
matter,  supported  on  a  piece  of  charcoal,  or 
fixed  in  a  ring  at  the  end  of  a  fine  platinum 
wire,  can  thus  in  an  instant  be  exposed  to  a  very 
high  degree  of  heat  under  these  contrasted  cir- 
cumstances, and  observations  of  great  value  made 
in  a  very  short  time.  The  use  of  the  instrument 
requires  an  even  and  uninterrupted  blast  of 
some  duration,  by  a  method  easily  acquired  with 
a  little  patience  ;  it  consists  in  employing  for 
the  purpose  the  muscles  of  the  cheeks  alone, 
respiration  being  conducted  through  the  nostrils, 
and  the  mouth  from  time  to  time  replenished 
with  air  without  intermission  of  the  blast. 

The  Argand  lamp,  adapted  to  burn  either  oil 
or  spirit,  but  especially  the  latter,  is  a  very 
useful  piece  of  chemical  apparatus.  In  this 
lamp  the  wick  is  cylindrical,  the  flame  being 
supplied  with  air  both  inside  and  outside;  the 
combustion  is  greatly  aided  by  the  chimney, 
which  is  made  of  copper  when  the  lamp  is  used 
as  a  source  of  heat.  Fig.  116  exhibits,  in  sec- 
tion, an  excellent  lamp  of  this  kind  for  burning 
alcohol  or  wood-spirit.  It  is  constructed  of  thin 
copper,  and  furnished  with  ground  caps  to  the 
wick-holder  and  aperture '  by  which  the  spirit  is 
introduced,  in  order  to  prevent  loss  when  the 
lamp  is  not  in  use.     Glass  spirit-lamps,  fitted 

Fig.  116. 


Fig.  114. 


Fig.  115. 


Fig.  117. 


'  When  in  use  this  aperture  must,  always  he  open,  otherwise  an  accident  is  pure  to  happen, 
the  beat  expands  the  air  in  the  lamp,  and  the  spirit  is  forced  out  in  a  state  of  inflammation. 


160 


COMBUSTION,    AND 


Fig.  119. 


with  caps  (fig.  117)  to  prevent  evaporation,  are  very  convenient  for  occa- 
sional use,  being  always  ready  and  in  order.* 

In  London,  and  other  large  towns  where  coal-gas  is  to  be  had,  that  sub- 
stance is  constantly  used  with  the  greatest  economy  and  advantage  in  every 
respect  as  a  source  of  heat.  Retorts,  flasks,  capsules, 
and  other  vessels,  can  be  thus  exposed  to  an  easily  re- 
gulated and  invariable  temperature  for  many  successive 
hours.  Small  platinum  crucibles  may  be  ignited  to 
redness  by  placing  them  over  the  flame  on  a  little  wire 
triangle.  The  arrangement  shown  in  fig.  119,  consist- 
ing of  a  common  Argand  gas-burner  fixed  on  a  heavy 
and  low  foot,  and  connected  with  a  flexible  tube  of 
caoutchouc  or  other  material,  leaves  nothing  to  desire. 

The  kindling-point,  or  temperature  at  which  combus- 
tion commences,  is  very  difi'erent  with  diff"erent  substan- 
ces ;  phosphorus  will  sometimes  take  fire  in  the  hand  ; 
sulphur  requires  a  temperature  exceeding  that  of  boil- 
ing water ;  charcoal  must  be  heated  to  redness.    Among 
gaseous  bodies  the  same  fact  is  observed :  hydrogen  is 
inflamed  by  a  red-hot  wire ;  carbonetted  hydrogen  re- 
quires a  white  heat  to  eff'ect  the  same  thing.    When  flame 
is  cooled  by  any  means  below  the  temperature  at  which  the  rapid  oxidation 
of  the  combustible  gas  occurs,  it  is  at  once  extinguished.     Upon  this  depends 
the  principle  of  Sir  H.  Davy's  invaluable  safe-lamp. 

Mention  has  already  been  made  of  the  frequent  disengagement  of  great 
quantities  of  light  carbonetted  hydrogen  gas  in  coal-mines.  This  gas,  mixed 
with  seven  or  eight  times  its  volume  of  atmospheric  air,  becomes  highly  ex- 
plosive, taking  fire  at  a  light,  and  burning  with  a  pale  blue  flame ;  and  many 
fearful  accidents  have  occurred  from  the  ignition  of  large  quantities  of 
mixed  air  and  gas  occupying  the  extensive  galleries  and  workings  of  a 
mine.  Sir  H.  Davy  undertook  an  investigation  with  a  view  to  discover  some 
remedy  for  this  constantly-occurring  calamity ;  his  labours  resulted  in  some 
exceedingly  important  discoveries  respecting  flame,  of  which  the  substance 
has  been  given,  and  which  led  to  the  construction  of  the  lamp  which  bears 
his  name. 

When  two  vessels  filled  with  a  gaseous  explosive  mixture  are  connected  by 
a  narrow  tube,  and  the  contents  of  one  fired  by  the  electric  spark,  or  other- 
wise, the  flame  is  not  communicated  to  the  other,  provided  the  diameter  of 
the  tube,  its  length,  and  the  conducting  power  for  heat  of  its  material,  bear 
a  certain  proportion  to  each  other ;  the  flame  is  extinguished  by  cooling,  and 
its  transmission  rendered  impossible. 

In  this  experiment,  high  conducting  power  and  diminished  diameter  com- 
pensate for  diminution  of  length ;  and  to  such  an  extent  can  this  be  carried, 


Fig.  118. 


*  The  spirit-lamp  represented  in  fig.  118,  is 
one  contrived  by  Dr.  Mitchell.  "It  is  made 
of  tinned  iron.  The  alcohol  is  poured  out  by 
means  of  the  hollow  handle,  and  is  admitted 
to  the  cylindrical  burner  by  two  or  three 
tubes  which  are  placed  at  the  very  bottom  ©f 
the  fountain.  By  such  an  arrangement  of 
parts,  the  alcohol  may  be  added  as  it  is  con- 
sumed, and  the  flame  kept  uniform;  and  aa 
the  pipes  which  pass  to  the  burner  are  so  re- 
mote from  the  flame,  the  alcohol  never  be- 
comes heated  bo  as  to  fly  off  through  the 
vent-hole,  and  thus  to  cause  greater  waste 
and  danger  of  explosion." 

A  cylindrical  chimney  is  an  advantageous 
addition  for  many  purposes.  It  may  be  madti 
of  tin-plate  or  copper.  —  R.  B. 


THE     STRUCTURE     OF     FLA.  ME 


161 


Fig.  120. 


that  metallic  gauze,  which  may  be  looked  upon  as  a  series  of  very  short 
square  tubes  arranged  side  by  side,  arrests  in  the  most  complete  manner  the 
passage  of  flame  in  explosive  mixtures,  when  of  sufficient 
degx-ee  of  fineness,  depending  upon  the  inflammability  of  the 
gas.  Most  providentially,  the  fire-damp  mixture  has  an  ex- 
ceedingly high  kindling  point ;  a  red  heat  does  not  cause  in- 
flammation ;  consequently,  the  gauze  will  be  safe  for  this 
substance,  when  flame  would  pass  in  almost  any  other  case. 

The  miner's  safe-lamp  (fig.  120)  is  merely  an  ordinary  oil- 
lamp,  the  flame  of  which  is  enclosed  in  a  cage  of  wire  gauze  ; 
made  double  at  the  upper  part,  containing  about  400  aper- 
tures to  the  square  inch.  The  tube  for  supplying  oil  to  the 
reservoir  reaches  nearly  to  the  bottom  of  the  latter,  while  the 
wick  admits  of  being  trimmed  by  a  bent  wire  passing  with 
friction  through  a  small  tube  in  the  body  of  the  lamp;  the 
flame  can  thus  be  kept  burning  for  any  length  of  time,  with- 
out the  necessity  of  unscrewing  the  cage.  When  this  lamp  is 
taken  into  an  explosive  atmosphere,  although  the  fire-damp 
may  burn  within  the  cage  with  such  energy  as  sometimes 
to  heat  the  metallic  tissue  to  dull  redness,  the  flame  is  not 
communicated  to  the  mixture  on  the  outside. 

These  efl'ects  may  be  conveniently  studied  by  suspending 
the  lamp  in  a  large  glass  jar,  and  gradually  admitting  coal- 
gas  below.  The  oil-flame  is  at  first  elongated,  and  then,  as 
the  proportion  of  gas  increases,  extinguished,  while  the  in- 
terior of  the  gauze  cylinder  becomes  filled  with  the  burn- 
ing mixture  of  gas  and  air.  As  the  atmosphere  becomes 
purer,  the  wick  is  once  more  relighted.  These  appear- 
ances are  so  remarkable,  that  the  lamp  becomes  an  admi- 
rable indicator  of  the  state  of  the  air  in  difi'erent  parts  of 
the  mine.' 

The  same  great  principle  has  been  ingeniously  applied 
by  Mr,  Hemming  to  the  construction  of  the  oxy-hydrogea 
safety-jet  formerly  mentioned.  This  is  a  tube  of  brass 
about  four  inches  long,  filled  with  straight  pieces  of  fine 
brass  wire,  the  whole  being  tightly  wedged  together  by  a 
pointed  rod,  forcibly  driven  into  the  centre  of  the  bundle. 
Fig.  121,  The  arrangement  thus  presents  a  series  of 
metal  tubes,  very  long  in  proportion  to  their  diameter,  the 
cooling  powers  of  which  are  so  great  as  to  prevent  the  pos- 
sibility of  the  passage  of  flame,  even  with  oxygen  and  hy- 
drogen, Thejetmay  be  used,  as  before  mentioned,  with 
a  common  bladder,  without  a  chance  of  explosion.  The 
fundamental  fact  of  flame  being  extinguished  by  contact 
with  a  cold  body,  may  be  elegantly  shown  by  twisting  a 
copper  wire  (fig.  122)  into  a  short  spiral,  about  01  inch 

Fig.  122, 


Fig.  121, 


*  This  is  the  true  use  of  the  lamp,  namely,  to  permit  the  viewer  or  superintendent,  with 
out  risk  to  himself,  to  examine  the  state  of  the  air  in  every  part  of  the  mine ;  not  to  enable 
workmen  to  continue  their  labours  in  an  atmosphere  habitually  explosive,  which  must  be 
unfit  for  human  respiration,  although  the  evil  effects  may  be  slow  to  appear.  Owners  of 
coal-mines  should  be  compelled  eitlier  to  adopt  efileient  nveajis  of  ventilation,  or  to  clos** 
workings  of  this  dangerous  character  altogether. 


162  NITROGEN     AND     HYDROGEN;     AMMONIA. 

in  diameter,  and  then  passing  it  cold  over  the  flame  of  a  wax  candle ;  the 
latter  is  extinguished.  If  the  spiral  be  now  heated  to  redness  by  a  spirit- 
lamp,  and  the  experiment  repeated,  no  such  effect  follows.* 

NITROGEN    AND    HTDEOGEN ;    AMMONIA. 

When  powdered  sal-ammoniac  is  mixed  with  moist  hydrate  of  lime,  and 
gently  heated  in  a  glass  flask,  a  large  quantity  of  gaseous  matter  is  disengaged, 
which  must  be  collected  over  mercury,  or  by  displacement,  advantage  being 
taken  of  its  low  specific  gravity. 

Ammoniacal  gas  thus  obtained  is  colourless ;  it  has  a  very  powerful  pun- 
gent odour,  and  a  strong  alkaline  reaction  to  test-paper,  by  which  it  may  be 
at  once  distinguished  from  nearly  all  other  bodies  possessing  the  same  physi- 
cal characters.  Under  a  pressure  of  6-5  atmospheres  at  60°  (15° -oC),  am- 
monia condenses  to  the  liquid  form.'*  Water  dissolves  about  700  times  its 
volume  of  this  remarkable  gas,  forming  a  solution  which  in  a  more  dilute 
state  has  long  been  known  under  the  name  of  liquor  ammonice ;  by  heat,  a 
great  part  is  again  expelled.  The  solution  is  decomposed  by  chlorine,  sal- 
ammoniac  being  formed,  and  nitrogen  set  free. 

Ammonia  has  a  density  of  0-589;  100  cubic  inches  weigh  18-26  grains. 
It  cannot  be  formed  by  the  direct  union  of  its  elements,  although  it  is  some- 
times produced  under  rather  remarkable  circumstances  by  the  deoxidation 
of  nitric  acid.  The  great  sources  of  ammonia  are  the  feebly-compounded 
azotized  principles  of  the  animal  and  vegetable  kingdoms,  which,  when  left 
to  putrefactive  change,  or  subjected  to  destructive  distillation,  almost  inva- 
riably give  rise  to  an  abundant  production  of  this  substance. 

The  analysis  of  ammoniacal  gas  is  easily  effected.  When  a  portion  is  con- 
fined in  a  graduated  tube  over  mercury,  and  electric  sparks  passed  through 
it  for  a  considerable  time,  the  volume  of  the  gas  gradually  increases  until  it 
becomes  doubled.  On  examination,  the  tube  is  found  to  contain  a  mixture 
of  3  measures  hydrogen  gas,  and  1  measure  nitrogen.  Every  two  volumes 
of  the  ammonia,  therefore,  contained  three  volumes  of  hydrogen  and  one  of 
nitrogen,  the  whole  being  condensed  to  the  extent  of  one-half.  The  weight 
of  the  two  constituents  will  be  in  the  pi-oportion  of  3  parts  hydrogen  to  14 
parts  nitrogen. 

Ammonia  may  also  be  decomposed  into  its  elements  by  transmission 
through  a  red-hot  tube. 

Solution  of  ammonia  is  a  very  valuable  reagent,  and  is  employed  in  a  great 
number  of  chemical  operations,  for  some  of  which  it  is  necessary  to  have  it 
perfectly  pure.     The  best  mode  of  preparation  is  the  following : — 

Equal  weights  of  sal-ammoniac  and  quicklime  are  taken  ;  the  lime  is  slaked 
in  a  covered  basin,  and  the  salt  reduced  to  powder.  These  are  mixed,  and 
introduced  into  the  flask  employed  in  preparing  solution  of  hydrochloric 
acid,  together  with  just  enough  water  to  damp  the  mixture,  and  cause  it  to 
aggregate  into  lumps ;  the  rest  of  the  apparatus  is  arranged  exactly  as  in 

*  Where  coal-gas  is  to  be  had,  it  may  be  adTantageously  used  as  a  source  of  heat,  by  taking 
advantage  of  the  above-mentioned  fact.  On  passing  a  current  of  gas  through  a  wide  vertical 
tube,  open  at  the  bottom  to  afford  a  free  mixture  with  atmospheric  air,  but  closed  at  ine  top 
by  wire  gauze,  and  then  kindling  the  mixture  after  its  escape  through  the  meshes,  it  will 
burn  with  feeble  illuminating  power,  but  no  loss  of  heat.  When  the  proportion  of  the  gas 
to  the  utmosphei-ic  air  is  such  as  not  to  allow  the  flame  to  become  yellow,  the  combustion 
will  be  complete,  and  no  carbonaceous  deposit  will  be  formed  on  cold  bodies  held  over  the 
tiumes.  The  length  and  diameter  of  the  cylinder  are  determined  by  the  amount  of  gas  to  be 
burni,  and  the  length  may  be  much  decreased  by  interposing  a  second  diaphragm  of  wire 
gauze  about  mid-length  of  the  cylinder,  the  current  of  gas  being  introduced  below  this,  by 
which  means  a  more  thorough  and  rapid  mixture  is  made  with  the  atmospheric  air.  —  Sir 
•lohn  Kobinson,  K.  H.  &c.,  Ed.  New  Phif.  Journal,  1840.— R.  B. 

»  At  the  temperature  of  — 103°  ( —  75°C),  liquid  ammonia  freezes  into  a  colourless  solid, 
hwAvicr  than  the  liquid  Itself —(Faraday.)— R.  B, 


NITROGEN     AND     BORON.  163 

the  former  case,  with  an  ounce  or  two  of  water  in  the  wash-bottle,  or  enough 
to  cover  the  ends  of  the  tubes,  and  the  gas  conducted  afterwards  into  pure 
distilled  water,  artificially  cooled,  as  before.  The  cork -joints  are  made  tight 
with  wax,  a  little  water  is  put  into  the  safety-funnel,  heat  cautiously  applied 
to  the  flask,  and  the  whole  left  to  itself.  The  disengagement  of  ammonia  is 
very  regular  and  uniform.  Chloride  of  calcium,  with  excess  of  hydrate  of 
lime,  rem*ains  in  the  flask.' 

The  decomposition  of  the  salt  is  usually  represented  in  the  manner  shown 
by  the  subjoined  diagram. 

{Ammonia Ammonia. 
Hydrochloric    ^  Hydrogen 'Z-"^  Water, 
acid 


I-™-  {  ?:&" ^Chloride  of 

calcium. 

Solution  of  ammonia  should  be  perfectly  colourless,  leave  no  residue  on 
evaporation,  and  when  supersaturated  by  nitric  acid,  give  no  cloud  or  mud- 
diness  with  nitrate  of  silver.  Its  density  diminishes  with  its  strength,  that 
of  the  most  concentrated  being  about  0-875 ;  the  value  in  alkali  of  any 
sample  of  liquor  ammoniae  is  most  safely  inferred,  not  from  a  knowledge 
of  its  density,  but  from  the  quantity  of  acid  a  given  amount  will  saturate. 
The  mode  of  conducting  this  experiment  will  be  found  described  under 
Alkalimetry. 

When  solution  of  ammonia  is  mixed  with  acids  of  various  kinds,  salts  are 
generated,  which  resemble  in  the  most  complete  manner  the  corresponding 
compounds  of  potassa  and  soda ;  these  are  best  discussed  in  connexion  with 
the  latter.  Any  ammoniacal  salt  can  at  once  be  recognized  by  the  evolution 
of  ammonia  when  it  is  heated  with  hydrate  of  lime,  or  solution  of  carbonate 
of  potassa  or  soda. 

NITROGEN    AND    BORON. 

A  combination  of  nitrogen  with  boron  was  first  obtained  by  Balmain. 
Woehler  prepared  it  by  mixing  one  part  of  pure  dry  borax  with  two  parts  of 
dry  sal-ammoniac,  heating  to  redness,  boiling  with  water  and  hydrochloric 
acid,  filtering  and  washing  with  hot  water,  when  the  compound  remained  in 
the  form  of  a  white  powder.  As  yet  it  has  not  been  obtained  quite  free 
from  oxygen. 

SULPHUR,    SELENIUM,    AND   PHOSPHORUS,    WITH   HYDROGEN. 

Sulphuretted  Hydrogen ;  Hydrosulphuric  Acid.  —  There  are  two  methods  by 
which  this  important  compound  can  be  readily  prepared,  namely,  by  '^he 
action  of  dilute  sulphuric  acid  upon  sulphide  of  iron,  and  by  the  decomposi- 
tion of  sulphide  of  antimony  by  hydrochloric  acid.  The  first  method  yield.>i 
it  most  easily,  and  the  second  in  the  purest  state. 

Protosulphide  of  iron  is  put  into  the  apparatus  for  hydrogen,  already 
several  times  mentioned,'  together  with  some  water,  and  oil  of  vitriol  is  added 
by  the  funnel,  until  a  copious  disengagement  of  gas  takes  place.  This  Is  to 
be  collected  over  tepid  water.     The  reaction  is  thus  explained  :  — 

»  See  Fig.  106,  p.  142. 


J64 


SULPHUR     WITH     HYDROGEN. 


Sulphide  of  iron  {  ^J'JP^"^ 

Water |  Hydrogen 

\  Oxygen  _ 

Sulphuric  acid 


Sulphuretted  hydrogen. 


Sulphate  of  protoxide  of  iron. 


By  the  other  plan,  finely-powdered  sulphide  of  antimony  is  put  into  a  flask, 
to  which  a  cork  and  bent  tube  can  be  adapted,  and  strong  liquid  hydro- 
chloric acid  poured  upon  it.  On  the  application  of  heat,  a  double  inter- 
change occurs  between  the  bodies  present,  sulphuretted  hydrogen  being 
formed,  and  chloride  of  antimony.  The  action  only  lasts  while  the  heat  is 
maintained. 


Hydrochloric  acid {  chlorife"' 

Sulphide  of  antimony  {  ^^^^^J^'^' 


Sulphuretted  hydrogen. 


-Chloride  of  antimony. 


Fig.  123. 


Sulphuretted  hydrogen  is  a  colourless  gas,  having  the  odour  of  putrid 
eggs ;  it  is  most  offensive  when  in  small  quantity,  when  a  mere  trace  is  pre- 
sent in  the  air.  It  is  not  irritating,  but,  on  the  contrary,  powerfully  narcotic. 
When  set  on  fire,  it  burns  with  a  blue  flame,  producing  water  and  sulphurous 
acid  when  the  supply  of  air  is  abundant ;  and  depositing  sulphur  when  the 
oxygen  is  deficient.  Mixed  with  chlorine,  it  is  instantly  decomposed,  with 
separation  of  the  whole  of  the  sulphur. 

This  gas  has  a  specific  gravity  of  1-171;  100  cubic  inches  weigh  36-33 
grains. 

A  pressure  of  17  atmospheres  at  50°  (10°C)  reduces 
it  to  the  liquid  form.  Cold  water  dissolves  its  own 
volume  of  sulphuretted  hydrogen,  and  the  solution 
is  often  directed  to  be  kept  as  a  test ;  it  is  so  prone 
to  decomposition,  however,  by  the  oxygen  of  the  air, 
that  it  speedily  spoils.  A  much  better  plan  is  to  keep 
a  little  apparatus  for  generating  the  gas  always  at 
hand,  and  ready  for  use  at  a  moment's  notice.  A  small 
bottle  or  flask  (fig.  123),  to  which  a  bit  of  bent  tube  is 
fittecf  by  a  cork,  is  supplied  with  a  little  sulphide  of 
iron  and  water;  when  required  for  use,  a  few  drops 
of  oil  of  vitriol  are  added,  and  the  gas  is  at  once 
evolved.  The  experiment  completed,  the  liquid  is 
poured  from  the  bottle,  replaced  by  a  little  clean  water, 
and  the  instrument  is  again  ready  for  use. 

When  potassium  is  heated  in  sulphuretted  hydrogen,  the  metal  burns  with 
great  energy,  becoming  converted  into  sulphide,  while  pure  hydrogen  remains, 
equal  in  volume  to  the  original  gas.  Taking  this  fact  into  account,  and 
comparing  the  density  of  the  gas  with  those  of  hydrogen  and  sulphur- vapour, 
it  appears  that  every  volume  of  sulphuretted  hydrogen  contains  one  volume 
of  hydrogen  and  one-sixth  of  a  volume  of  sulphur-vapour,  the  whole  con- 
densed into  one  volume.  This  corresponds  very  nearly  with  its  composition 
by  weight,  determined  by  other  means,  namely,  16  parts  sulphur  and  1  part 
liydrogen. 

When  a  mixture  is  made  of  100  measures  of  sulphuretted  hydrogen  and 
150  measures  of  pure  oxygen,  and  exploded  by  the  electric  spark,  complete 
combustion  ensues,  ana  100  measures  of  sulphurous  acid  gas  result. 

Sulphuretted  hydrogen  is  a  frequent  product  of  the  putrefaction  of  organic 
matter,  both  animal  and  vegetable ;  it  occurs  also  in  certain  mineral  springs, 
»s  at  Harrowgate,  and  elsewhere.     When  accidentally  present  in  the  atmo- 


PERSULPHIDE  OF  HYDROGEN.         165 

sphere  of  an  apartment,  it  may  be  instantaneously  destroyed  by  a  small 
quantity  of  chlorine  gas. 

There  are  few  reagents  of  greater  value  to  the  practical  chemist  than  this 
substance ;  when  brought  in  contact  with  many  metallic  solutions,  it  gives 
rise  to  precipitates,  which  are  often  exceedingly  characteristic  in  appearance, 
and  it  frequently  affords  the  means  also  of  separating  metals  from  each  other 
with  the  greatest  precision  and  certainty.  The  precipitates  spoken  of  are 
insoluble  sulphides,  formed  by  the  mutual  decomposition  of  the  metallic 
oxides  or  chlorides  and  sulphuretted  hydrogen,  water  or  hydrochloric  acid 
being  produced  at  the  same  time.  All  the  metals  are,  in  fact,  precipitated 
whose  sulphides  are  insoluble  in  water  and  in  dilute  acids. 

Sulphuretted  hydrogen  possesses  itself  the  properties  of  an  acid;  its 
solution  in  water  reddens  litmus  paper. 

The  best  test  for  the  presence  of  this  compound  is  paper  wetted  with 
solution  of  acetate  of  lead.  This  salt  is  blackened  by  the  smallest  trace  of 
the  gas. 

Persulphide  of  Hydrogen.  —  This  substance  corresponds  in  constitution 
and  instability  to  the  binoxide  of  hydrogen ;  it  is  prepared  by  the  following 
means :  — 

Equal  weights  of  slaked  lime  and  flowers  of  sulphur  are  boiled  with  5  or 
6  parts  of  water  for  half  an  hour,  when  a  deep  orange-coloured  solution  is 
produced,  containing  among  other  things  persulphide  of  calcium.  This  is 
filtered,  and  slowly  added  to  an  excess  of  dilute  sulphuric  acid,  with  constant 
agitation.  A  white  precipitate  of  separated  sulphur  and  sulphate  of  lime 
makes  its  appearance,  together  with  a  quantity  of  yellow  oDy-looking 
matter,  which  collects  at  the  bottom  of  the  vessel ;  this  is  persulphide  of 
hydrogen.^ 

If  the  experiment  be  conducted  by  pouring  the  acid  into  the  solution  of 
sulphide,  then  nothing  but  finely-divided  precipitated  sulphur  is  obtained. 

The  persulphide  is  a  yellow,  viscid,  insoluble  liquid,  exhaling  the  odour 
of  sulphuretted  hydrogen;  its  specific  gravity  is  1-769.  It  is  slowly  decom- 
posed even  in  the  cold  into  sulphur  and  sulphuretted  hydrogen,  and  instantly 
by  a  higher  temperature,  or  by  contact  with  many  metallic  oxides.  This 
compound  probably  contains  twice  as  much  sulphur  in  relation  to  the  other 
elements,  as  sulphuretted  hydrogen. 

Hydrogen  and  Selenium  ;  Selenietted  Hydrogen. — This  substance  is  produced 
by  the  action  of  dilute  sulphuric  acid  upon  selenide  of  potassium  or  iron ; 
it  very  much  resembles  sulphuretted  hydrogen,  being  a  colourless  gas,  freely 

*  The  reaction  which  ensnes  when  hydrate  of  lime,  sulphur,  and  water,  are  hoiled  together, 
is  rather  complex;  bisulphide  or  pentasulphide  of  calcium  being  formed,  together  with  hypo 
Bulphite  of  lime,  arising  from  the  transfer  of  the  oxygen  of  the  decomposed  lime  to  another 
portion  of  sulphur. 

2  ea  lime  \  ^  ^^-  <^^'*^^"°^  ->  2  eq.  bisulphide  of  calcium. 

^*  12  eq.  oxygen  .  '" 


■  1  eq.  hyposulphurous  acid. 
The  bisulphide  of  calcium,  decomposed  by  an  acid  under  favourable  circumstances,  yields  • 
salt  of  lime  and  bisulphide  (persulphide;  of  hydrogen. 

1  eq.  bisulp.  calcium  j  ^  eq.  sulp^hur --^^  1  eq.  bisulphide  of  hydrogen. 


1  eq.  water \  }  ^-  ^lyt^rogeu 

^  }  1  eq.  oxygen 

Sulphuric  acid -^==^^  "^  ^l-  sulphate  of  Ume. 

When  the  acid  is  poured  into  the  sulphide,  sulphuretted  hydrogen,  water,  and  sulphate  of 
lime,  are  produced,  while  the  excess  of  sulphur  is  thrown  down  as  a  fine  white  powder,  the 
"precipitated  sulphur"  of  the  Pharmacopoeia.  When  the  object  is  to  prepare  the  latter  Bub- 
stance,  hydrochloric  acid  must  be  used  in  the  place  of  sulphuric. 


166  PHOSPHORUS    WITH     HYDROGEN. 

soluble  in  water,  and  decomposing  metallic  solutions  like  that  suLtance  ;  in- 
soluble selenides  are  thus  produced.  This  gas  is  said  to  act  very  powerfully 
upon  the  lining  membrane  of  the  nose,  exciting  catarrhal  symptoms,  and 
destroying  the  sense  of  smell.  It  contains  39-6  parts  selenium,  and  1  part 
hydrogen. 

Phosphorus  and  Hydrogen  ;  Pkosphoretted  Hydrogen.  —  This  body  bears  a 
slight  analogy  in  some  of  its  chemical  relations  to  ammoniacal  gas ;  it  is, 
however,  destitute  of  alkaline  properties. 

Phosphoretted  hydrogen  may  be  obtained  in  a  state  of  purity  by  heating 
in  a  small  retort  hydrated  phosphorous  acid,  which  is  by  such  treatment  de- 
composed into  phosphoretted  hydrogen  and  hydrated  phosphoric  acid.* 

Thus  obtained,  the  gas  has  a  density  of  1-24.  It  contains  32  parts  phos- 
phorus, and  3  parts  hydrogen,  and  is  so  constituted  that  every  two  volumes 
contain  3  volumes  of  hydrogen  and  half  a  volume  of  phosphorus-vapour, 
condensed  into  two  volumes.  It  possesses  a  highly  disagreeable  odour  of 
garlic,  is  slightly  soluble  in  water,  and  burns  with  a  brilliant  white  flame, 
forming  water  and  phosphoric  acid. 

Phosphoretted  hydrogen  may  also  be  produced  by  boiling  together  in  a 
retort  of  small  dimensions  caustic  potassa  or  hydrate  of  lime,  water,  and 
phosphorus ;  the  vessel  should  be  filled  to  the  neck,  and  thq  extremity  of 
the  latter  made  to  dip  into  the  water  of  the  pneumatic  trough.  In  the  reaction 
which  ensues  the  water  is  decomposed,  and  both  its  elements  combine  with 
the  phosphorus.  The  alkali  acts  by  its  presence  determining  the  decomposition 
of  the  water,  in  the  same  manner  as  sulphuric  acid  determines  the  decompo- 
sition of  water  when  in  contact  with  zinc. 

Water       /  Hydrogen --^::^=^  Phosphoretted  hydrogen. 

...  "^Oxygen 


Phosphorus . 

Phosphorus^ _^^^ 

Lime  -~==rs^  TTypnphnsphitft  of  lime. 

The  phosphoretted  hydrogen  prepared  by  the  latter  process  has  the  sin- 
gular property  of  spontaneous  inflammability  when  admitted  into  the  air  or 
into  oxygen  gas;  with  the  latter,  the  experiment  is  very  beautiful,  but  re- 
quires caution ;  the  bubbles  should  be  singly  admitted.  When  kept  over 
water  for  some  time,  the  gas  loses  this  property,  without  otherwise  suff'ering 
any  appreciable  change  :  but  if  dried  by  chloride  of  calcium,  it  may  be  kept 
•unaltered  for  a  much  longer  period.  M.  Paul  Th6nard  has  shown  that  the 
ipontaneous  combustibility  of  the  gas  arises  from  the  presence  of  the  vapour 
of  a  liquid  phosphide  of  hydrogen,  which  can  be  procured  in  small  quantity, 
by  conveying  the  gas  produced  by  the  action  of  the  water  on  phosphide  of 
calcium  through  a  tube  cooled  by  a  freezing  mixture.  This  substance  forms 
A  colourless  liquid  of  high  refractive  power  and  very  great  volatility.  It  does 
Hot  freeze  at  0°  (  — 17° -80).  In  contact  with  air  it  inflames  instantly,  and 
lis  vapour  in  very  small  quantity  communicates  spontaneous  inflammability 
lo  pure  phosphoretted  hydrogen,  and  to  all  other  combustible  gases.  It  is 
decomposed  by  light  into  gaseous  phosphoretted  hydrogen,  and  a  solid  phos- 
,»hide  which  is  often  seen  on  the  inside  of  jars  containing  gas  which  has  lost 

•  Decomposition  of  hydrated  phosphorous  acid  by  heat :  — 

,1  eq.  phosphoretted  hydrogen,  PHj 


i  tq.  hydtafed 
;^»l  odphorous 


Hydrated  phos- 
phoric  acid. 


NITROGEN  WITH  CHLORINE,  ETC.      167 

the  property  of  spontaneous  inflammation  by  exposure  to  light.  Strong 
acida  occasion  its  instantaneous  decomposition.  Its  instability  is  equal  to 
that  of  binoxide  of  hydrogen.  It  is  to  be  observed  that  the  pure  phospho- 
retted  hydrogen  gas  itself  becomes  spontanemisly  inflammable  if  heated  to 
the  temperature  of  boiling  water,* 

Phosphoretted  hydrogen  decomposes  several  metallic  solutions,  giving  rise 
to  precipitates  of  insoluble  phosphides.  With  hydriodic  acid  it  forms  a  crys- 
talline compound  somewhat  resembling  sal-ammoniac. 

NITROGEN   WITH    CHLORINK    AND    IODINE. 

Chloride  of  Nitrogen. — When  sal-ammoniac  or  nitrate  of  ammonia  is  dis- 
solved in  water,  and  a  jar  of  chlorine  gas  inverted  into  the  solution,  the  gas 
is  absorbed,  and  a  deep  yellow  oily  liquid  is  observed  to  collect  upon  the 
surface  of  the  solution,  which  ultimately  sinks  in  globules  to  the  bottom. 
This  is  chloride  of  nitrogen,  the  most  dangerously-explosive  substance  known. 
The  following  is  the  safest  method  of  conducting  the  expenment : — 

A  somewhat  dilute  and  tepid  solution  of  pure  sal-ammoniac  in  distilled 
water  is  poured  into  a  clean  basin,  and  a  bottle  of  chlorine,  the  neck  of 
which  is  quite  free  from  grease,  inverted  into  it.  A  shallow  and  heavy  leaden 
cup  is  placed  beneath  the  mouth  of  the  bottle  to  collect  the  product.  When 
enough  has  been  obtained,  the  leaden  vessel  may  be  withdrawn  with  its  dan- 
gerous contents,  the  chloi-ide  remaining  covered  with  a  stratum  of  water. 
The  operator  should  protect  his  face  with  a  strong  wire-gauze  mask  when 
experimenting  upon  this  substance. 

The  change  is  explained  by  the  following  diagram  :- 

Chlorine — ^^==-Chloride  of  nitrogen. 

Chlorine ,^  """^"Z^^'  Hydrochloric  acid 

{^  Nitrogen  -"^"^^^ 
)  Hydrogen  " 
Hydrochloric  acid -Hydrochloric  acid. 

Chloride  of  nitrogen  is  very  volatile,  and  its  vapour  is  exceedingly  irrita- 
ting to  the  eyes.  It  has  a  specific  gravity  of  1  -653.  It  may  be  distilled  at 
160°  (71°-1C),  although  the  experiment  is  attended  with  great  danger. 
Between  200°  (93° -SC)  and  212°  (100°C)  it  explodes  with  the  most  fearful 
violence.  Contact  with  almost  any  combustible  matter,  as  oil  or  fat  of  any 
kind,  determines  the  explosion  at  common  temperatures ;  a  vessel  of  porce- 
lain, glass,  or  even  of  cast-iron,  is  broken  to  pieces,  and  the  leaden  cup 
receives  a  deep  indentation.  This  body  has  usually  been  supposed  to  contain 
nitrogen  and  chlorine  in  the  proportion  of  14  parts  of  the  former  to  106-5 
parts  of  the  latter,  but  recent  experiments  upon  the  corresponding  iodine- 
compound  induce  a  belief  that  it  contains  hydrogen.'* 

Iodide  of  Nitrogen.  —  When  finely-powdered  iodine  is  put  into  caustic  am- 
monia it  is  in  part  dissolved,  giving  a  deep  brown  solution,  and  the  residue 
is  converted  into  a  blacli  powder,  which  is  the  substance  in  question.  The 
brown  liquid  consists  of  hydriodic  acid  holding  iodine  in  solution,  and  is 
easily  separated  from  the  solid  product  by  a  filter.  The  latter  while  still 
wet  is  distributed  in  small  quantities  upon  separate  pieces  of  bibulous  paper, 
and  left  to  dry  in  the  air. 

Iodide  of  nitrogen  is  a  black  insoluble  powder,  which,  when  dry,  explodes 
with  the  slightest  touch,  even  that  of  a  feather ;  and  sometimes  without  any 
obvious  cause.     The  explosion  is  not  nearly  so  violent  as  that  of  the  com- 

»  Ann.  Chim.  et  Phys.  3rd  series,  xiv.  5.  According  to  M.  Th^nard,  the  new  liquid  phosphide 
of  hydrogen  contains  PHa  and  the  solid  PaH.    The  gas  is  represented  by  the  formula  PH3. 
•  Instead  of  NCla,  it  may  in  reality  be  NH  Cla. 


168  OTHER     COMPOUNDS    OF 

pound  ^ast  described,  and  is  attended  with  the  production  of  violent  fumes 
of  iodine.  Dr.  Gladstone  has  proved  that  this  substance  contains  hydrogen, 
and  that  it  may  be  viewed  as  ammonia,  in  which  two- thirds  of  the  hydrogen 
are  replaced  by  iodine. 

OTHER    COMPOUNDS    OF    NON-METALLIC    ELKMENTS. 

Chlorine  with  Sulphur  and  Phosphorus. — Chloride  of  Sulphur. — The  subchlo- 
ride  is  easily  prepared  by  passing  dry  chlorine  over  the  surface  of  sulphur 
kept  melted  in  a  small  glass  retort  connected  with  a  good  condensing  ar- 
rangement. The  chloride  distils  over  as  a  deep  orange-yellow  mobile  liquid, 
of  peculiar  and  disagreeable  odour,  which  boils  at  280°  (137°-8C).  As  this 
substance  dissolves  both  sulphur  and  chlorine,  it  is  not  easy  to  obtain  it  in  a 
pure  and  definite  state.     It  contains  32  parts  sulphur  and  35-5  chlorine.* 

Subchloride  of  sulphur  is  instantly  decomposed  by  water ;  hydrochloric 
and  hyposulphurous  acids  are  formed,  and  sulphur  separated.  The  hypo- 
Bulphurous  acid  in  its  turn  decomposes  into  sulphur  and  sulphurous  acid. 

Protochloride  of  sulphur  is  formed  by  exposing  the  above  compound  for  a 
considerable  time  to  the  action  of  chlorine,  and  then  distilling  it  in  a  stream 
of  the  gas.  It  has  a  deep  red  colour,  is  heavier  than  water,  boils  at  147° 
(63°'9C),  and  contains  twice  as  much  chlorine  as  the  subchloride.' 

Chlorides  of  Phosphorus. — Terchloride.^ — This  is  prepared  in  the  same  man- 
ner as  subchloride  of  sulphur,  by  gently  heating  phosphorus  in  dry  chlorine 
gas,  the  phosphorus  being  in  excess.  Or,  by  passing  the  vapour  of  phos- 
phorus over  fragments  of  calomel  (subchloride  of  mercury)  contained  in  a 
glass  tube  and  strongly  heated.  It  is  a  colourless,  thin  liquid,  which  fumes 
in  the  air,  and  possesses  a  powerful  and  offensive  odour.  Its  specific  gravity 
is  1-45.  Thrown  into  water,  it  sinks  to  the  bottom  of  that  liquid,  and  be- 
comes slowly  decomposed,  yielding  phosphorous  acid  and  hydrochloric  acid. 
This  compound  contains  32  parts  phosphorus,  and  106-5  parts  chlorine. 

Pentachloride  of  Phosphorus.*  —  The  compound  formed  when  phosphorus  is 
burned  in  excess  of  chlorine.  Into  a  large  retort,  fitted  with  a  cap  and  stop- 
cock, pieces  of  phosphorus  are  introduced;  the  retort  is  then  exhausted,  and 
filled  with  dry  chlorine  gas.  The  phosphorus  takes  fire,  and  burns  with  a 
pale  flame,  forming  a  white,  volatile,  crystalline  sublimate,  which  is  the  pen- 
tachloride. It  may  be  obtained  in  larger  quantity  by  passing  a  stream  of 
chlorine  gas  into  the  preceding  liquid  terchloride,  which  becomes  gradually 
converted  into  a  solid,  crystalline  mass.  Pentachloride  of  phosphorus  is 
decomposed  by  water,  yielding  phosphoric  and  hydrochloric  acids. 

Two  bromides  of  phosphorus  are  known,  closely  corresponding  in  proper- 
ties and  constitution  with  the  chlorides.  Several  compounds  of  iodine  and 
phosphorus  appear  to  exist:  they  are  fusible  crystalline  substances,  which 
decompose  by  contact  with  water,  and  yield  hydriodic  and  phosphorous,  or 
phosphoric  acid. 

Chlorine  and  Carbon.  —  Several  compounds  of  chlorine  and  carbon  are 
known.  They  are  obtained  indirectly  by  the  action  of  chlorine  upon  certain 
organic  compounds,  and  are  described  in  connection  with  the  history  of 
alcohol,  &c. 

Iodine  with  Sulphur  and  Phosphorus.  —  These  compounds  are  formed  by 
gently  heating  together  the  materials  in  vessels  from  which  the  air  is  ex- 
cluded.    They  present  few  points  of  interest. 

Chlorine  with  Iodine. — Iodine  readily  absorbs  chlorine' gas,  forming,  when 
the  cnlorine  is  in  excess,  a  solid,  yellow  compound,  and  when  the  iodine  pre- 
ponderates, a  brown  liquid.  The  solid  iodide  is  decomposed  by  water,  yield- 
ing hydrochloric  and  iodic  acids.* 

«  SgCl.  » SCI.  »  PCla.  « PC1», 

■  Hemce  it  doubtless  contains  1  eq.  iodine,  and  5  eq  chlorine,  or  IClt. 


NON-MEI'ALLIC    ELEMENTS.  169 

Another  definite  compound  is  formed  by  heating  in  a  retort  a  mixture  of 
1  part  iodine  and  4  parts  chlorate  of  potassa ;  oxygen-gas  and  chloride  of 
iodine  are  disengaged,  and  the  latter  may  be  condensed  by  suitable  means, 
lodate  and  perchlorate  of  potassa  remain  in  the  retort. 

This  chloride  of  iodine  is  a  yellow,  oily  liquid,  of  suffocating  smell  and 
astringent  taste ;  it  is  soluble  in  water  and  alcohol  without  decomposition. 
It  probably  consists  of  127  parts  iodine,  and  35-5  parts  chlorine.' 

Carbon  and  Sulphur. — Bisulphide  of  Carbon.  —  A  wide  porcelain  tube  is 
filled  with  pieces  of  charcoal,  which  have  been  recently  heated  to  redness  in  a 
jovered  crucible,  and  fixed  across  a  furnace  in  a  slightly  inclined  position, 
[nto  the  lower  extremity  a  tolerably  wide  tube  is  secured  by  the  aid  of  a 
cork ;  this  tube  bends  downwards,  and  passes  nearly  to  the  bottom  of  a  bottle 
filled  with  fragments  of  ice  and  a  little  water.  The  porcelain  tube  being 
heated  to  a  bright  redness,  fragments  of  sulphur  are  thrown  into  the  open 
end,  which  is  immediately  afterwards  stopped  by  a  cork.  The  sulphur 
melts,  and  becomes  converted  into  vapour,  which,  at  that  high  temperature, 
combines  with  the  carbon,  forming  an  exceedingly  volatile  compound,  which 
is  condensed  by  the  ice  and  collects  at  the  bottom  of  the  vessel.  This  is 
collected  and  re-distilled  with  very  gentle  heat  in  a  retort  connected  with  a 
good  condenser.  Bisulphide  of  carbon  is  a  transparent  colourless  liquid  of 
great  refractive  and  dispersive  power.  Its  density  is  1-272.  It  boils  at  110° 
(43°-3C),  and  emits  vapour  of  considerable  elasticity  at  common  temper- 
atures. The  odour  of  this  substance  is  very  repulsive.  When  set  on  fire  in 
the  air  it  burns  with  a  blue  flame,  forming  carbonic  acid  and  sulphurous 
acid  gases ;  and  when  its  vapour  is  mixed  with  oxygen  it  becomes  explosive. 

It  freely  dissolves  sulphur,  and  by  spontaneous  evaporation  deposits  the 
latter  in  beautiful  crystals  ;  it  also  dissolves  phosphorus 

Chlorides  of  Silicium  and  Boron. — Both  silicium  and  boron  combine  directly 
with  chlorine.  The  chloride  of  silicium  is  most  easily  obtained  by  mixing 
finely-divided  silica  with  charcoal-powder  and  oil,  strongly  heating  the  mix- 
ture in  a  covered  crucible,  and  then  exposing  the  mass  so  obtained  in  a  por- 
celain tube,  heated  to  full  redness,  to  the  action  of  perfectly  dry  chlorine 
gas.  A  good  condensing  arrangement,  supplied  with  ice-cold  water,  must 
be  connected  with  the  porcelain  tube.  The  product  is  a  colourless  and  very 
volatile  liquid,  boiling  at  122°  (50°C),  of  pungent,  suffocating  odour.  In 
contact  with  water  it  yields  hydrochloric  acid  and  gelatinous  silica.  This 
substance  contains  21-3  parts  silicium,  and  106-5  chlorine.* 

Bromide  of  Silicium  may  be  obtained  by  a  similar  proceeding,  the  vapour 
of  bromine  being  substituted  for  chlorine ;  it  resembles  the  chloride,  but  is 
less  volatile. 

Chloride  of  Boron  is  a  permanent  gas,  decomposed  by  water  with  produc- 
tion of  boracic  and  hydrochloric  acids,  and  fuming  strongly  in  the  air.  It 
may  be  most  easily  obtained  by  exposing  to  the  action  of  dry  chlorine  at  a 
very  high  temperature  an  intimate  mixture  of  glassy  boracic  acid  and  char- 
coal.    It  resembles  in  constitution  chloride  of  silicium. 

•  Or  single  equivalents.  »  Or  SiCI». 


16 


170  GENERAL    PRINCIPLES    OJ? 


ON  THE  GENERAL  PRINCIPLES  OF  CHEMICAL  PHILOSOPHY 


The  study  of  the  non-metallic  elements  can  be  pushed  to  a  very  consider 
able  extent,  and  a  large  amount  of  precise  and  exceedingly  important  infor- 
mation acquired,  without  much  direct  reference  to  the  great  fundamental 
laws  of  chemical  union ;  the  subject  cannot  be  discussed  in  this  manner  com- 
pletely, as  will  be  obvious  from  occasional  cases  of  anticipation  in  many  of 
the  foregoing  foot-notes ;  still,  much  may  be  done  by  this  simple  method  of 
proceeding.  The  bodies  themselves,  in  their  combinations,  furnish  admirable 
illustrations  of  the  general  laws  referred  to,  but  the  study  of  their  leading 
characters  and  relations  does  not  of  necessity  involve  a  previous  knowledge 
of  these  laws  themselves. 

It  is  thought  that  by  such  an  arrangement  the  comprehension  of  these 
very  important  general  principles  may  become  in  some  measure  facilitated 
by  constant  references  to  examples  of  combinations,  the  elements  and  pro- 
ducts of  which  have  been  already  described.  So  much  more  difificult  is  it  to 
gain  a  clear  and  distinct  idea  of  any  proposition  of  great  generality  from  a 
simple  enunciation,  than  to  understand  the  bearing  of  the  same  law  when 
illustrated  by  a  single  good  and  familiar  instance. 

Before  proceeding  farther,  however,  it  is  absolutely  necessary  that  these 
matters  should  be  discussed ;  the  metallic  compounds  are  so  numerous  and 
complicated,  that  the  establishment  of  some  general  principle,  some  con- 
necting link,  becomes  indispensable.  The  doctrine  of  equivalents,  and  the 
laws  which  regulate  the  formation  of  saline  compounds,  supply  this  defi- 
ciency. 

In  the  organic  department  of  the  science,  the  most  interesting  perhaps  of 
all,  a  knowledge  of  these  principles,  and,  farther,  an  acquaintance  or  even 
familiarity  with  the  beautiful  system  of  chemical  notation  now  in  use,  are 
absolutely  required.  This  latter  is  found  of  very  great  service  in  the  study 
of  salts  and  other  complex  inorganic  compounds,  but  in  that  of  organic 
chemistry  it  cannot  be  dispensed  with. 

It  will  be  proper  to  commence  with  a  notice  of  the  principles  which  regu- 
late the  modern  nomenclature  in  use  in  chemical  writings. 

NOMENCLATURE. 

In  the  early  days  of  chemistry  the  arbitrary  and  fanciful  names  which 
were  conferrea  by  each  experimenter  on  the  new  compounds  he  discovered 
sufficed  to  distinguish  these  from  each  other,  and  to  render  intelligible  the 
description  given  of  their  production.  Such  terms  as  oil  of  vitriol,  spirit  of 
salt,  oil  of  tartar,  butter  of  antimony,  sugar  of  lead,  flowers  of  zinc,  sal  enixum, 
sal  mirabile,  &c.,  were  then  quite  admissible.  In  process  of  time,  however, 
when  the  number  of  known  substances  became  vastly  increased,  the  confu- 
sion of  language  produced  by  the  want  of  a  more  systematic  kind  of  nomen- 
clature became  quite  intolerable,  and  the  evil  was  still  farther  increased  by 
the  frequent  use  of  numerous  synonyms  to  designate  the  same  substance. 

Id  the  year  1787,  Lavoisier  and  his  colleagues  published  the  plan  of  the 


CHEMICAL    PHILOSOPHY.  171 

remarkable  system  of  nomenclature,  which,  with  some  important  extensions 
since  rendered  necessary,  has  up  to  the  present  time  to  a  great  extent  satisfied 
the  wants  of  the  science.  It  is  in  organic  chemistry  that  the  deficiencies  of 
this  plan  are  chiefly  felt,  and  that  something  like  a  return  to  the  old  method 
has  been  rendered  inevitable.  Organic  chemistry  is  an  entirely  new  science 
which  has  sprung  up  since  the  death  of  these  eminent  men,  and  has  to  deal 
with  bodies  of  a  constitution  or  type  difi'ering  completely  from  that  of  the 
inorganic  acids,  bases  and  salts  which  formed  the  subjects  of  the  chemical 
studies  of  that  period.  The  rapid  progress  of  discovery,  by  which  new  com- 
pounds, and  new  classes  of  compounds,  often  of  the  most  unexpected  nature, 
are  continually  brought  to  light,  sufi&ciently  proves  that  the  time  to  attempt 
the  construction  of  a  permanent  systematic  plan  of  naming  organic  bodies 
has  not  yet  arrived. 

The  principle  of  the  nomenclature  in  use  may  be  thus  explained : — Ele- 
mentary substances  still  receive  arbitrary  names,  generally,  but  not  always, 
referring  to  some  marked  peculiarity  of  the  body ;  an  uniformity  in  the  ter- 
mination of  the  word  has  generally  been  observed,  as  in  the  case  of  new 
metals  whose  names  are  made  to  end  in  ium. 

Compounds  formed  by  the  union  of  non-metallic  elements  with  metals,  or 
with  other  non-metallic  elements,  are  collected  into  groups  having  a  kind  of 
generic  name  derived  from  the  non-metallic  element,  or  that  most  opposed 
in  characters  to  a  metal,  and  made  to  terminate  in  ide.^  Thus  we  haVe 
oxides,  chlorides,  iodides,  bromides,  &c.,  of  hydrogen  and  of  the  several 
metals  ;  oxides  of  chlorine  ;  chlorides  of  iodine  and  sulphur ;  sulphides  and 
phosphides  of  hydrogen  and  the  metals. 

The  nomenclature  of  oxides  has  been  already  described  (p,  109).  They 
are  divided  into  three  classes,  namely,  alkaline  or  basic  oxides,  neutral 
oxides,  and  oxides  possessing  acid  characters.  In  practice  the  term  oxide 
is  usually  restricted  to  bodies  belonging  to  the  first  two  groups,  those  of  the 
third  being  simply  called  acids.  Generally  speaking,  these  acids  are  derived 
from  the  non-metallic  elements,  which  yield  no  basic  oxides  ;  many  of  the 
metals,  however,  yield  acids  of  a  more  or  less  energetic  description. 

The  same  element  in  combining  with  oxygen  in  more  than  one  proportion 
may  yield  more  than  one  acid ;  in  this  case  it  has  been  usual  to  apply  to  the 
acid  containing  most  oxygen  the  termination  ic,  and  to  the  one  containing 
the  lesser  quantity  the  termination  ous.  When  more  members  of  the  same 
group  came  to  be  known,  recourse  was  had  to  a  prefix,  hypo  or  hyper,  (or 
per,)  signifying  deficiency  or  excess.  Thus,  the  two  earliest  known  acids 
of  sulphur  were  named  respectively  sulphurous  and  sulphuric  acids ;  subse- 
quently two  more  were  discovered,  the  one  containing  less  oxygen  than 
sulphurous  acid,  the  other  intermediate  in  composition  between  sulphurous 
and  sulphuric  acids.  These  were  called  hyposulphurom  and  hyposulphuric 
acids.  The  names  of  the  new  acids  of  sulphur  of  still  more  recent  discovery 
are  not  yet  permanently  fixed ;  Lavoisier's  system,  even  in  its  extended  form, 
fails  to  furnish  names  for  such  a  lengthened  series.  Other  examples  of  the 
nomenclature  of  acids  with  increasing  proportions  of  oxygen  are  easily  found  ; 
as  hypophosphor ous, phosphorous  Siud phosphoric  acids;  hypochlorous,  chlorous, 
hypochloric,  chloric,  and  perchloric  Sicids;  nitrous,  hyponitric,  a,nd  nitric  acids,  &c. 

The  nomenclature  of  salts  is  derived  from  that  of  the  acid  they  contain ; 
if  the  name  of  the  acid  terminate  in  ic,  that  of  the  salt  is  made  to  end  in  ate  r 
if  in  ous,  that  of  the  saline  compounds  ends  in  ite.  Thus,  sulphuric  acid  forms 
sulphates  of  the  various  bases ;  sulphurous  acid,  sulphites  ;  hyposulphurous 
acid,  hyposulphites ;  hyposulphuric  acid,  hyposulphates,  &c.  The  rule  here  is 
very  simple  and  obvious. 

*  Formerly  the  termination  uret  was  likewise  firequently  used. 


172  GENERAL    PRINCIPLES    OF 

The  want  of  uniformity  in  the  application  of  the  systematic  nomenclature 
is  chiefly  felt  in  the  class  of  oxides  not  possessing  acid  characters,  and  in 
that  of  some  analogous  compounds.  The  old  rule  was  to  apply  the  word 
protoxide  to  the  oxide  containing  least  oxygen,  to  call  the  next  in  order  bin- 
oxide,  the  third  iritoxide,  or  teroxide ;  &c.  But  latterly  this  rule  has  been 
broken  through,  and  the  term  protoxide  given  to  that  oxide  of  a  series  in 
which  the  basic  characters  are  most  strongly  marked.  Any  compound  con- 
taining a  smaller  proportion  of  oxygen  than  this  is  called  a  suboxide.  An 
example  is  to  be  found  in  the  two  oxides  of  copper ;  that  which  was  once 
called  binoxide  is  now  protoxide,  being  the  most  basic  of  the  two,  while  the 
former  protoxide  is  degraded  into  suboxide. 

The  Latin  prefix  per,  or  rarely  hi/per,  is  sometimes  used  to  indicate  the 
highest  oxide  of  a  series  destitute  of  acidity,  as  peroxide  of  iron,  chromium, 
manganese,  lead,  &c.  Other  Latin  prefixes,  as  sesgui,  bi  or  bin,  and  quad, 
applied  to  the  name  of  binary  compounds  or  salts,  have  reference  to  the  con- 
stitution of  these  latter  expressed  in  chemical  equivalents.'  Thus,  an  oxide 
in  which  the  proportion  of  oxygen  and  metal  are  in  equivalents,  as  1-5  to  1,  or 
3  to  2,  is  often  called  a  sesqUioxide ;  if  in  the  proportion  of  2  to  1,  a  binoxide, 
&c.  The  same  terms  are  applied  to  salts ;  thus  we  have  neutral  sulphate  of 
potassa,  sesquisutphate  of  potassa,  and  bisulphate  of  potassa ;  the  first  con- 
taining 1  equivalent  of  acid  to  1  of  base,  the  second  1-5  of  acid  to  1  of  base, 
and  the  third  2  equivalents  of  acid  to  1  equivalent  of  base.  In  like  mannei 
we  have  neutral  oxalate,  binoxalatc,  and  quadroxalate  of  potassa,  the  latte* 
having  4  eq.  of  acid  to  1  eq.  of  base.     Many  other  cases  might  be  cited. 

The  student  will  soon  discover  that  the  rules  of  nomenclature  are  ofter 
loosely  applied,  as  when  a  Latin  numeral  prefix  is  substituted  for  one  of 
Greek  origin.  We  speak  of  tersulphide  instead  of  tritosulphide  of  antimony 
These  and  other  small  irregularities  are  not  found  in  practice  to  cause  seri 
ous  confusion. 

THE    LAWS    OF   COMBINATION   BY  WEIGHT. 

The  great  general  laws  which  regulate  all  chemical  combinatirvn«»  admit  of 
being  laid  down  in  a  manner  at  once  simple  and  concise.  They  are  four  ir 
number,  and  to  the  following  effect : — 

1.  All  chemical  compounds  are  definite  in  their  nature,  the  r?t'o  of  th':, 
elements  being  constant. 

2.  When  any  body  is  capable  of  uniting  with  a  second  in  several  pro- 
portions, these  proportions  bear  a  simple  relation  to  each  other. , 

3.  If  a  body,  A,  unite  with  other  bodies,  B,  C,  D,  the  quantities  of 
B,  C,  D,  which  unite  with  A,  represent  the  relations  in  which  they  unite 
among  themselves,  in  the  event  of  union  taking  place. 

4.  The  combining  quantity  of  a  compound  is  the  sum  of  the  combining 
quantities  of  its  components. 

(1.)  Constancy  of  Composition. — That  the  same  chemical  compound  invari- 
ably contains  the  same  elements  united  in  unvarying  proportions,  is  a  propo- 
sition almost  axiomatic;  it  is  involved  in  the  very  idea  of  identity  itself. 
The  converse,  however,  is  very  far  from  being  true ;  the  same  elements  com- 
bining in  the  same  proportions  do  not  of  necessity  generate  the  same 
substance. 

Organic  chemistry  furnishes  numerous  instances  of  this  very  remarkable 

fact,  in  which  the  greatest  diversity  of  properties  is  associated  with  identity 

^of  chemical  composition.    These  cases  seem  to  be  nearly  confined  to  organic 

'  8«e  a  few  pages  forward. 


CHEMICAL    PHILOSOPHY.  173 

chemistry ;  only  a  few  weTl-establisbed  and  undoubted  examples  being  known 
in  tb^^ganic  or  mineral  division  of  the  science. 
P^g^^^i^.p-^ultijple  Proportions. — Illustrations  of  this  simple  and  beautiful  law 
^T^bound  on  every  side ;  let  the  reader  take  for  example  the  compounds  of 
"'  ^   nitrogen  and  oxygen,  five  in  number,  containing  the  proportions  of  the  two 
elements  so  described  that  the  quantity  of  one  of  them  shall  remain  con- 
stant : — 

Nitrogen.       Oxygen. 

Protoxide 14  8 

Binoxide  14  16 

Nitrous  acid  14  24 

Hyponitric  acid  14  32 

Nitric  acid 14  40 

It  will  be  seen  at  a  glance,  that  while  the  nitrogen  remains  the  same,  the 
quantities  of  oxygen  increase  by  multiples  of  8,  or  the  number  representing 
the  quantity  of  that  substance  in  the  first  compound;  thus  8,  8x2,  8x3, 
8x4,  and  8x5,  give  respectively  the  oxygen  in  the  protoxide,  the  binoxide, 
nitrous  acid,  hyponitric  acid,  and  lastly,  nitric  acid.  Again,  carbonic  acid 
contains  exactly  twice  as  much  oxygen  in  proportion  to  the  other  constituent 
as  carbonic  oxide ;  the  binoxide  of  hydrogen  is  twice  as  rich  in  oxygen  as 
water ;  the  correspouding  sulphides  exhibit  the  same  phenomena,  while  the 
metallic  compounds  oflFer  one  continued  series  of  illustrations  of  the  law, 
although  the  ratio  is  not  always  so  simple  as  that  of  1  to  2. 

It  often  happens  that  one  or  more  members  of  a  series  are  yet  deficient : 
the  oxides  of  chlorine  afford  an  example 

Chlorine.       Oxygen. 

Hypochlorous  acid  35-6  8 

Chlorous  acid 85-5  24 

H3'pochloric  acid 35-5  32 

Chloric  acid 35-5  40 

Perchloric  acid 35-6  66 

Here  the  quantities  of  oxygen  progi'ess  in  the  following  order: — 8,  8x3, 
8x4,  8x5,  8x7  ;  a  gap  is  manifest  between  the  first  and  second  substances; 
this  remains  to  be  filled  up  by  future  researches.  The  existence  of  a  simple 
relation  among  the  numbers  in  the  second  column  is  however  not  the  less 
evident.  Even  when  difficulties  seem  to  occur  in  applying  this  principle, 
they  are  only  apparent,  and  vanish  when  closely  examined.  In  the  highly 
complex  sulphur  series,  given  at  p.  132,  the  numbers  placed  in  each  column 
are  multiples  of  the  lowest  amongst  them ;  and,  by  making  the  assumption, 
which  is  not  at  all  extravagant,  that  certain  of  the  last-named  bodies  are  in- 
termediate combinations,  we  may  arrange  the  four  direct  compounds  in  such 
%  manner  that  the  sulphur  shall  remain  a  constant  quantity. 

Sulphur.       Oxygen. 

Hyposulphurous  acid 32  16 

Sulphurous  acid 32  ,.  32 

Hyposulphuric  acid 32  .....  40 

Sulphuric  acid 32  .......  48 

Compound  bodies  of  all  kinds  are  also  subject  to  the  law  of  multiples 
when  they  unite  among  themselves,  or  with  elementary  substances.  There 
are  two  sulphates  of  potassa  and  soda :  the  second  contains  twice  as  much 
acid  in  relation  to  the  alkaline  base  as  the  first.  There  are  three  oxalates 
of  potassa,  namely,  the  simple  oxalate,  the  binoxalate,  and  the  quadroxalat© ; 
15* 


174  GENERAL    PRINCIPLES    OP 

tlie  second  has  equally  twice  as  much  acid  as  the  first ;  and  the  third  twice 
as  much  as  the  second.  Many  other  cases  might  be  cited,  but  the  student, 
once  in  possession  of  the  principle,  will  easily  notice  them  as  he  proceeds. 

(3.)  Law  of  Equivalents,  — It  is  highly  important  that  the  subject  now  to 
be  discussed  should  be  completely  understood. 

Let  a  substance  be  chosen  whose  range  of  aflBnity  and  powers  of  combi- 
nation are  very  great,  and  whose  compounds  are  susceptible  of  rigid  and 
exact  analysis ;  such  a  body  is  found  in  oxygen,  which  is  known  to  unite 
with  all  the  elementary  substances,  with  the  single  exception  of  fluorine. 
Now,  let  a  series  of  exact  experiments  be  made  to  determine  the  proportions 
in  which  the  different  elements  combine  with  one  and  the  same  constant 
quantity  of  oxygen,  which,  for  reasons  hereafter  to  be  explained,  may  be 
assumed  to  be  8  parts  by  weight ;  and  let  these  numbers  be  arranged  in  a 
column  opposite  the  names  of  the  substances.  The  result  is  a  table  or  list 
like  the  following,  but  of  course  much  more  extensive  when  complete. 

Oxygen 8 

Hydrogen 1 

Nitrogen 14 

Carbon 6 

Sulphur 16 

Phosphorus , 32 

Chlorine 35-5 

Iodine 127 

Potassium 39 

Iron 28 

Copper 81-7 

Lead 103-7 

Silver 108 

&c.  &c. 

Now  the  law  in  question  is  to  this  effect :  —  If  such  numbers  represent 
the  proportions  in  which  the  different  elements  combine  with  the  arbitrarily- 
fixed  quantity  of  the  starting  substance,  the  oxygen,  they  also  represent  the 
proportions  in  which  they  unite  among  themselves^  or  at  any  rate  bear  some  ex- 
ceedingly simple  ratio  to  these  proportions. 

Thus,  hydrogen  and  chlorine  combine  invariably  in  the  proportions  1  and 
35-5;  hydrogen  and  sulphur,  1  to  16;  chlorine  and  silver,  35-5  to  108; 
iodine  and  potassium,  127  parts  of  the  former  to  39  of  the  latter,  &c.  This 
rule  is  never  departed  from  in  any  one  instance. 

The  term  equivalent  is  applied  to  these  numbers  for  a  reason  which  will 
now  be  perfectly  intelligible ;  they  represent  quantities  capable  of  exactly 
replacing  each  other  in  combination :  1  part  of  hydrogen  goes  as  far  in  com- 
bining with  or  saturating  a  certain  amount  of  oxygen  as  28  parts  of  iron,  39 
of  potassium,  or  108  of  silver ;  for  the  same  reasons,  the  numbers  are  said 
to  represent  combining  quantities,  or  proportionals. 

Nothing  is  more  common  than  to  speak  of  so  many  equivalents  of  this  or 
that  substance  being  united  to  one  or  more  equivalents  of  a  second ;  by  this 
expression,  quantities  are  meant  just  so  many  times  greater  than  these  rela- 
tive numbers.  Thus,  sulphuric  acid  is  said  to  contain  1  equivalent  of  sul- 
phur and  3  equivalents  of  oxygen ;  that  is,  a  quantity  of  the  latter  repre- 
sented by  three  times  the  combining  number  of  oxygen ;  phosphoric  acid  is 
made  up  of  1  equivalent  of  phosphorus  and  5  of  oxygen ;  the  red  oxide  of 
iron  contains,  as  will  be  seen  hereafter,  3  equivalents  of  oxygen  to  every  2 
equivalents  of  metal,  &c.     It  is  an  expression  which  will  henceforward  be 


CHEMICAL    PHILOSOPHY,  1?5 

freely  and  constantly  employed ;  it  is  hoped,  therefore,  that  it  will  be  under- 
stood. 

The  nature  of  the  law  will  easily  show  that  the  choice  of  the  body  destined 
to  serve  for  a  point  of  departure  is  perfectly  arbitrary,  and  regulated  by  con- 
siderations of  convenience  alone. 

A  body  might  be  chosen  which  refuses  to  unite  with  a  considerable  num- 
ber of  the  elements,  and  yet  the  equivalents  of  the  latter  would  admit  of 
being  determined  by  indirect  means,  in  virtue  of  the  very  peculiar  law  under 
discussion.  Oxygen  does  not  unite  with  fluorine,  yet  the  equivalent  of  the 
latter  can  be  found  by  observing  the  quantity  which  combines  with  the  equi- 
valent quantity  of  hydrogen  or  calcium,  already  known.  We  may  rest  as- 
sured that  if  an  oxide  of  fluorine  be  ever  discovered,  its  elements  will  be 
associated  in  the  ratio  of  8  to  19,  or  in  numbers  which  are  either  multiples 
or  submultiples  of  these. 

The  number  assigned  to  the  starting-substance  is  also  equally  arbitrary ; 
if,  in  the  table  given,  oxygen  instead  of  8  were  made  10,  or  100,  or  even  a 
fractional  number,  it  is  quite  obvious  that  although  the  other  numbers  would 
all  be  difi'erent,  the  ratio,  or  proportion  among  the  whole,  would  remain  un- 
changed, and  the  law  would  still  be  maintained  in  all  its  integrity. 

There  are  in  fact  two  such  tables  in  use  among  chemists ;  one  in  which 
oxygen  is  made  =  8,  and  a  second  in  which  it  is  made  =  100 ;  the  former 
is  generally  used  in  this  country  and  England,  and  the  latter  still  to  a 
certain  extent  on  the  Continent.  The  only  reason  for  giving,  as  in  the  pre- 
sent volume,  a  preference  to  the  first  is,  that  the  numbers  are  smaller  and 
more  easily  remembered. 

The  number  8  has  been  chosen  in  this  table  to  represent  oxygen,  from  an 
opinion  long  held  by  the  late  Dr.  Prout,  and  recently  to  appearance  substan- 
tiated in  some  remarkable  instances  by  very  elaborate  investigation,  that  the 
equivalents  of  all  bodies  are  multiplies  of  that  of  hydrogen ;  and,  conse- 
quently, by  making  the  latter  unity,  the  numbers  would  be  all  integers.  The 
question  must  be  considered  as  altogether  unsettled.  A  great  obstacle  to 
such  a  view  is  presented  by  the  case  of  chlorine,  which  certainly  seems  to  be 
a  fractional  number ;  and  one  single  well-established  exception  will  be  fatal 
to  the  hypothefsis. 

As  all  experimental  investigations  are  attended  with  a  certain  amount  of 
error,  the  results  contained  in  the  following  table  must  be  looked  upon 
merely  as  good  approximations  to  the  truth.  For  the  same  reason,  small 
differences  are  often  observed  in  the  determination  of  the  equivalents  of  the 
same  bodies  by  difl'ereut  experimenters.  '. 


176 


GENERAL    PRINCIPLES    OF 


TABLE    OF    ELEMENTABY   SUBSTANCES,    WITH   THEIR   EQUIVALENTS. 


Oxy.  =  8. 

Aluminium...,  13-7 

Antimony 129 

Arsenic 75 

Barium 68-5 

Beryllium 6-9 

Bismuth 213 

Boron 10-9 

Bromine 80 

Cadmium 56 

Calcium 20 

Carbon 6 

Cerium 47  (?) 

Chlorine 35-5 

Chromium 26-7 

Cobalt 29-5 

Copper 31-7 

Didymium 50  (?) 

Erbium 

Fluorine 19 

Gold 197 

Hydrogen 1 

Iodine 127 

Iridium 99 

Iron 28 

Lanthanum  ...  47  (?) 

Lead 103-7 

Lithium 6-5 

Magnesium  ...  12 
Manganese....  27-6 

Mercury 100 

Molybdenum..  46 


)xy.  =  100. 

Oxy.=8. 

Oxy.=100. 

171-25 

Nickel 

...  29-6 

370 

1612-5 

Niobium 

937-5 

Nitrogen.... 

...  14 

175 

856-25 

Norium 

86-25 

Osmium 

...  99-6 

1245 

2662-5 

Oxygen  

...     8 

100 

136-25 

Palladium .. 

...  63-3 

666-25 

1000 

Pelopium 

700 

Phosphorus. 

...  32 

400 

250 

Platinum.... 

...  98-7 

1233-75 

75 

Potassium .. 

...  39 

487-5 

587-5 

Rhodium  ... 

...  52-2 

652-5 

443-75 

Ruthenium . 

...  52-2 

652-5 

333-75 

Selenium  ... 

...  39-5 

493-75 

368-75 

Silicium 

...  21-3 

266-25 

396-25 

Silver 

.  108 

1350 

625 

Sodium 

...  23 

287-5 

Strontium... 

...  43-8 

547-5 

237.5 

Sulphur 

...  16 

200 

2462-5 

Tantalum... 

...184 

2300 

12-5 

Tellurium... 

...  64-2 

802-5 

1587-5 

Terbium 

1237-5 

Thorium .... 

..,  59-6 

745 

350 

Tin 

...  58 

725 

587-5 

Titanium  ... 

...  25 

312-5 

1296-25 

Tungsten.... 

...  92 

1150 

81-25 

Uranium.... 

...  60 

760 

150 

Vanadium.. 

...  68-6 

857-6 

345 

Yttrium 

1250 

Zinc  

...  32-6 

407-5 

575 

Zirconium.. 

...  33-6 

420 

(4.)  Combining  Numbers  of  Compounds. — The  law  states  that  the  equivalent 
or  combining  number  of  a  compound  is  always  the  sum  of  the  equivalents 
of  its  components.  This  is  also  a  great  fundamental  truth,  which  it  is  neces- 
sary to  place  in  a  clear  and  conspicuous  light.  It  is  a  separate  and  inde- 
pendent law,  established  by  direct  experimental  evidence,  and  not  deducible 
from  either  of  the  preceding. 

The  method  of  investigation  by  which  the  equivalent  of  a  simple  body  is 
determined,  has  been  already  explained ;  that  employed  in  the  case  of  a  com- 
pound is  in  nowise  different.  The  example  of  the  acids  and  alkalis  may  be 
taken  as  the  most  explicit,  and  at  the  same  time  most  important.  An  acid 
and  a  base,  combined  in  certain  definite  proportions,  neutralize,  or  mask  each 
other's  properties  completely,  and  the  result  is  a  salt ;  these  proportions  are 
called  the  equivalents  of  the  bodies,  and  they  are  very  variable.  Some  acids 
have  very  high  capacities  of  saturation,  of  others  a  much  larger  quantity 
must  be  employed  to  neutralize  the  same  amount  of  base ;  the  bases  them- 
selves present  also  similar  phenomena.  Thus,  to  saturate  47  parts  of  potassa, 
or  116  parts  of  oxide  of  silver,  there  are  required 


CHEMICAL    PHILOSOPHY.  177 

40  parts  sulphuric  acid, 
64      *'     nitric  acid, 
75-5  "     chloric  acid, 
167       "     iodic  acid, 
51       "     acetic  acid. 

Numbers  very  different,  but  representing  quantities  which  replace  each 
other  in  combination.  Now,  if  a  quantity  of  some  base,  such  as  potassa,  be 
taken,  which  is  represented  by  the  sum  of  the  equivalents  of  potassium  and 
oxygen,  then  the  quantity  of  any  acid  requisite  for  its  neutralization,  as  de- 
termined by  direct  experiment,  will  always  be  found  equal  to  the  sum  of  the 
equivalents  of  the  different  components  of  the  acid  itself. 

39= equivalent  of  potassium. 
8=  '*  oxygen. 

47= assumed  equivalent  of  potassa. 

47  parts  of  potassa  are  found  to  be  exactly  neutralized  by  40  parts  of  real 
sulphuric  acid,  or  by  54  parts  of  real  nitric  acid.  These  quantities  are 
evidently  made  up  by  adding  together  the  equivalents  of  their  constituents : — 

1  eqjoivalent  of  sulphur  =16  1  equivalent  of  nitrogen  =  14 

3  *'  oxygen  =  24  5  "  oxygen  =  40 

1       "       sulphuric  acid  =  40  1  "        nitric  acid  =  54 

And  the  same  is  true  if  any  acid  be  taken,  and  the  quantities  of  different 
bases  required  for  its  neutralization  determined ;  the  combining  number 
of  the  compound  will  always  be  found  to  be  the  sum  of  the  combining  num- 
bers of  its  components,  however  complex  the  substance  may  be.  Even 
among  such  bodies  as  the  vegeto-alkalis  of  organic  chemistry,  the  same  uni- 
versal rule  holds  good.  When  salts  combine,  which  is  a  thing  of  very  com- 
mon occurrence,  as  will  hereafter  be  seen,  it  is  always  in  the  ratio  of  the 
equivalent  numbers.  Apart  from  hypothetical  consideration,  no  d  priori 
reason  can  be  shown  why  such  should  be  the  case  ;  it  is,  as  before  remarked, 
an  independent  law,  established  like  the  rest,  by  experiment. 


A  curious  observation  was  very  early  made  to  this  effect : — If  two  neuira . 
salts  which  decompose  each  other  when  mixed,  be  brought  in  contact,  the 
new  compounds  resulting  from  their  mutual  decomposition  will  also  be  neutral. 
For  example,  when  solution  of  nitrate  baryta  and  sulphate  of  potassa  are 
mingled,  they  both  suffer  decomposition,  sulphate  of  baryta  and  nitrate  of 
potassa  being  simultaneously  formed,  both  of  which  are  perfectly  neutral. 
The  reason  of  this  will  be  at  once  evident;  interchange  of  elements  can 
only  take  place  by  the  displacement  of  equivalent  quantities  of  matter  on 
either  side.  For  every  54  parts  of  nitric  acid  set  free  by  the  decomposition 
of  the  barytic  salt,  47  parts  of  potassa  are  abandoned  by  the  40  parts  of 
sulphuric  acid  with  which  they  were  previously  in  combination,  now  trans- 
ferred to  the  baryta.  But  54  and  47  are  the  representatives  of  combining 
quantities ;  hence  the  new  compound  must  be  neutrai 

COMBINATION    BY   VOLUME, 

Many  years  ago,  M.  Gay-Lussac  made  the  very  important  and  interestrag 
discovery  that  when  gases  combine  chemically,  union  invariably  takes  place 
either  between  equal  volumes,  or  between  volumes  which  bear  a  simple  rela- 
tion to  each  other.     This  is  not  only  true  of  elementary  gases,  but  of  com 


?.78  GENERAL     PRINCIPLES    OP 

^ouud  bodies  of  this  description,  as  it  is  invariably  observed  that  the  con- 
Iraction  of  bulk  which  so  frequently  follows  combination  itself  also  bears  a 
simple  relation  to  the  volumes  of  the  combining  gases.  The  consequence 
of  this  is,  that  compound  gases  and  the  vapours  of  complex  volatile  liquids 
(which  are  truly  gases  to  all  intents  and  purposes)  follow  the  same  law  as 
elementary  bodies,  when  they  unite  with  these  latter  or  combine  among  them- 
Belves. 

The  ultimate  reason  of  the  law  in  question  is  to  be  found  in  the  very 
remarkable  relation  established  by  the  hand  of  Nature  between  the  specific 
gravity  of  a  body  in  the  gaseous  state  and  its  chemical  equivalent ; —  a  rela- 
tion of  such  a  kind  that  quantities  by  weight  of  the  various  gases  expressed 
by  their  equivalents,  or  in  other  words,  quantities  by  weight  which  combine, 
occupy  under  similar  circumstances  of  pressure  and  temperature  either  equal 
volumes,  or  volumes  bearing  a  similar  proportion  to  each  other.  In  the 
example  cited  below,  equivalent  weights  of  hydrogen,  chlorine,  and  iodine- 
vapour,  occupy  equal  volumes,  while  the  equivalent  of  oxygen  occupies 
exactly  half  that  measure. 

Cubic  inches. 
8-0  grains  of  oxygen  occupy  at  60°  (15°-5C)  and  30  inches  barom.    23-3 

1-0  grain  of  hydrogen 46-7 

85-5  grains  of  chlorine 46-2 

127-0  grains  of  iodine-vapour  (would  measure) 46-7 

If  both  the  specific  gravity  and  the  chemical  equivalent  of  a  gas  be  known, 
its  equivalent  or  combining  volume  can  be  easily  determined,  since  it  will  be 
represented  by  the  number  of  times  the  weight  of  an  unit  of  volume  (the 
specific  gravity)  is  contained  in  the  weight  of  one  chemical  equivalent  of  the 
substance.  In  other  words,  the  equivalent  volume  is  found  by  dividing  the 
chemical  equivalent  by  the  specific  gravity.  The  following  table  exhibits 
the  relations  of  specific  gravity,  equivalent  weight,  and  equivalent  volume 
of  the  principal  elementary  substances. 

Sp.  gra'^ty.                   Equiv.  weight.  Equiv.  volume. 

Hydrogen 00693  1-0 14-43  or  1 

Nitrogen 0-972  14-0  14-37  "  1 

Chlorine 2-470  35-5  14-33  "  1 

Bromine-vopour 5-395  800  14-82  "  1 

Iodine-vapour 8-716  127-0  14-57  '*  1 

Carbon- vapour' 0-418  6-0  14-34  "  1 

Mercury-vapour 7-000  100-0  14-29  "  1 

Oxygen  1-106  80  7-23"^ 

Phosphorus-vapour 4-350  ...     320  735  "  | 

Arsenic-vapour  10-420  75-0  7-19  "  | 

Sulphur-vapour 6-654  160  2-40"^ 

Thus  it  appears  that  hydrogen,  nitrogen,  chlorine,  bromine,  iodine,  carbon, 
and  mercury,  in  the  gaseous  state,  have  the  same  equivalent  volume  ;  oxygen, 
phosphoi-us,  and  arsenic,  one-half  of  this ;  and  sulphur  one-sixth.  The 
falight  discrepancies  in  the  numbers  in  the  third  column  result  chiefly  from 
errors  in  the  determination  of  the  specific  gravities. 

Compound  bodies  exhibit  exactly  similar  results : — 


*  See  farther  on. 


CHEMICAL    PHILOSOPHY.  179 

gp.  gravity.    Equiv.  weight.    Equiv.  volume. 

Water-vapour 0-625     ....       90     ....     14-40  or  1 

Protoxide  of  nitrogen 1-625     ....     220     ....     14-43"! 

Sulphuretted  hydrogen 1-171     ....     17-0     ....     14-51   "  1 

Sulphurous  acid 2-210     ....     32-0     ....     14-52  "  1 

Carbonic  oxide 0-973     ....     14-0     ...      14-39  "  1 

Carbonic  acid  1-524     ....     220     ....     14-43"! 

Light  carbonetted  hydrogen 0-559     ....       80     ....     14-31  "  1 

Olefiantgas 0-981     ....     14-0     ....     14-27"! 

Binoxide  of  nitrogen 1-039     ....     30-0     ....     28-87  "  2 

Hydrochloric  acid  1-269     ....     365     ....     28-70  "  2 

Phosphoretted  hydrogen 1-240     ....     35-0     ....     28-22  "  2 

Ammonia 0589     ....     17-0     ....     28-86  "  2 

Ether-vapour 2-586     ....     370     ....     14-31  "  1 

Acetone-vapour  2-022     ....     290     ....     14-34  "  1 

Benzol-vapour  2-738     ....     78-0     ....     28-49  "  2 

Alcohol-vapour 1-613     ....     460     ....     28-52  "  2 

« 

In  the  preceding  tables  the  ordinary  standard  of  specific  gravity  for  gases, 
atmospheric  air,  has  been  taken.  It  is,  however,  a  matter  of  perfect  indif- 
ference what  substance  be  chosen  for  this  purpose  ;  the  numbers  represent- 
ing the  combining  volumes  will  change  with  the  divisor,  but  the  proportions 
they  bear  to  each  other  will  remain  unaltered.  And  the  same  remark 
applies  to  the  equivalent  weights-;  either  of  the  scales  in  use  may  be  taken, 
provided  that  it  be  adhered  to  throughout. 

The  law  of  volumes  often  serves  in  practice  to  check  and  corroborate  the 
results  of  experimental  investigation,  and  is  often  of  gi-eat  service  in  this 
respect. 

There  is  an  expression  sometimes  made  use  of  in  chemical  writings  which 
it  is  necessary  to  explain,  namely,  the  meaning  of  the  words  hypothetical  den- 
sity of  vapour,  applied  to  a  substance  which  has  never  been  volatilized,  such 
as  carbon,  whose  real  specific  gravity  in  that  state  must  of  course  be  un- 
known ;  it  is  easy  to  understand  the  origin  of  this  term..  Carbonic  acid  con- 
tains a  volume  of  oxygen  equal  to  its  own;  consequently,  if  the  specific 
gravity  of  the  latter  be  subtracted  from  that  of  the  former  gas,  the  residue 
will  express  the  proportion  borne  by  the  weight  of  the  carbon,  certainly 
then  in  a  vaporous  state,  to  that  of  the  two  gases. 

The  specific  gravity  of  carbonic  acid  is 1-5240 

That  of  oxygen  is 1-1057 


0-4183 


On  the  supposition  that  carbonic  acid  contains  equal  volumes  of  oxygen 
and  this  vapour  of  carbon,  condensed  to  one-half,  the  latter  will  have  the 
specific  gravity  represented  by  0-4183  and  the  combining  volume  given  in  the 
table.  But  this  is  merely  a  supposition,  a  guess ;  no  proof  can  be  given 
that  carbonic  acid  gas  is  so  constituted.  All  that  can  be  safely  said  is  con- 
tained in  the  prediction,  that,  should  the  specific  gravity  of  the  vapour  of 
carbon  ever  be  determined,  it  will  be  found  to  coincide  with  this  number,  or 
to  bear  some  simple  and  obvious  relation  to  it. 

For  many  years  past,  attempts  have  been  made  to  extend  to  solids  and 
liquids  the  results  of  Gay-Lussac's  discovery  of  the  law  of  gaseous  combi- 
nation by  volume,  the  combining  or  equivalent  volumes  of  the  bodies  in 
question  being  determined  by  the  method  pursued  in  the  case  of  gases, 
namely,  by  dividing  the  chemical  equivalent  by  the  specific  ,:^ravity.     The 


180 


GENERAL    PRINCIPLES    OF 


numbers  obtained  in  this  manner  representing  the  combining  volumes  of  the 
Yarious  solid  and  liquid  elementary  substances,  present  far  more  cases  of 
discrepancy  than  of  agreement.  The  latter  are,  however,  sufficiently  nu- 
merous to  excite  great  interest  in  the  investigation.  Some  of  the  results 
pointed  out  are  exceedingly  curious  as  far  as  they  go,  but  are  not  as  yet 
sufficient  to  justify  any  general  conclusion.  The  inquiry  is  beset  with  many 
great  difficulties,  chiefly  arising  from  the  unequal  expansion  of  solids  and 
liquids  by  heat,  and  the  great  differences  of  physical  state,  and  consequently 
of  specific  gravity,  often  presented  by  the  former. 

Such  is  a  brief  account  of  the  great  laws  by  which  chemical  combinations, 
of  every  kind,  are  governed  and  regulated ;  and  it  cannot  be  too  often  re- 
peated, that  the  discovery  of  these  beautiful  laws  has  been  the  result  of 
pure  experimental  inquiry.  They  have  been  established  on  this  firm  and 
stable  foundation  by  the  joint  labours  of  very  many  illustrious  men ;  they 
are  the  expression  of  fact,  and  are  totally  independent  of  all  hypotheses  or 
theories  whatsoever. 


CHEMICAL   NOTATION  ;    SYMBOLS. 

For  convenience  in  communicating  ideas  respecting  the  composition,  and 
supposed  constitution,  of  chemical  compounds,  and  explaining  in  a  clear  and 
simple  manner,  the  results  of  changes  they  may  happen  to  undergo,  re- 
course is  had  to  a  kind  of  written  symbolical  language,  the  principle  of 
which  must  now  be  explained.  To  represent  compounds  by  symbols  is  no 
novelty,  as  the  works  of  the  Alchemists  will  show,  but  these  have  been  mere 
arbitrary  marks  or  characters  invented  for  the  sake  of  brevity,  or  sometimes 
perhaps  for  that  of  obscurity. 

The  plan  about  to  be  described  is  due  to  Berzelius ;  it  has  been  adopted, 
with  slight  modifications,  wherever  chemistry  is  pursued. 

Every  elementary  substance  is  designated  by  the  first  letter  of  its  Latin 
name,  in  capital,  or  by  the  first  letter  conjoined  with  a  second  small  one,  the 
most  characteristic  in  the  word,  as  the  names  of  many  bodies  begin  alike. 
The  single  letter  is  usually  confined  to  the  earliest  discovered,  or  most  im- 
portant element.  Farther,  by  a  most  ingenious  idea,  the  symbol  is  made  to 
represent  not  the  substance  in  the  abstract,  but  one  equivalent  of  that  sub- 
stance. 

Table  of  Symbols  of  the  Elementary  Bodies. 


Aluminium Al 

Antimony  (Stibium) Sb 

Arsenic As 

Barium Ba 

Beryllium Be 

Bismuth Bi 

Boron Bo 

Bromine Br 

Cadmium Cd 

Calcium Ca 

Carbon C 

Cerium Ce 

Chlorine CI 

Chromium Cr 

Cobalt Co 

Copper  (Cuprum) Cu 

Didymium Dy 

Erbium Er 

Fluorine.. « F 


Gold  (Aurum) Au 

Hydrogen H 

Iodine I 

Iridium Ir 

Iron  (Ferrum)  Fe 

Lantanum Ln 

Lead  (Plumbum) Pb 

Lithium L 

Magnesium  Mg 

Manganese  Mn 

Mercury  ( Hydrargyrum) ....  Hg 

Molybdenum Mo 

Nickel Ni 

Niobium Nb 

Nitrogen N 

Norium  No 

Osmium Os 

Oxygen O 

Palladium Pd 


CHEMICAL    PHILOSUPHY, 


181 


Pelopium Pe 

Phosphorus P 

Platinum Pt 

Potassium  (Kalium) K 

Rhodium  R 

Ruthenium Ru 

Selenium  Se 

Silicium Si 

Silver  (Argentum)  Ag 

Sodium  (Natrium)  Na 

Strontium Sr 

Sulphur S 


Tantalum Ta 

Tellurium Te 

Terbium Tb 

Thorium I'h 

Tin  (Stannum) Sn 

Titanium Ti 

Tungsten  (Wolframium) W 

Vanadium V 

Uranium U 

Yttrium Y 

Zinc  Zn 

Zirconium Zr 


Combination  between  bodies  in  the  ratio  of  the  equivalents  is  expressed 
by  mere  juxtaposition  of  the  symbols,  or  sometimes  by  interposing  Uie  sign 
of  addition.     For  example :  — 

Water HO,  or  H  +  0 

Hydrochloric  acid  HCl,  or  H  +  CI 
Protoxide  of  iron  FeO,  or  Fe  -J-  0 

When  more  than  one  equivalent  is  intended,  a  suitable  number  is  added, 
sometimes  being  placed  before  the  symbol,  like  a  co-efficient  in  algebra, 
sometimes  appended  after  the  manner  of  an  exponent,  but  more  commonly 
placed  a  little  below  on  the  right. 

Binoxide  of  hydrogen  H  -}-  20,  or  HO',  or  HOj 

Sulphuric  acid 8  +  30,  or  SO",  or  SO3 

Hyposulphuric  acid..  2S4-60,  or  S^'  or  S^Og 

Combination  between  bodies  themselves  compound  is  indicated  by  the  sign 
of  addition,  or  by  a  comma.  When  both  are  used  in  the  same  formula,  the 
latter  may  be  very  conveniently  applied,  as  Professor  Graham  has  suggested, 
to  indicate  the  closest  and  most  intimate  union.  A  number  standing  before 
symbols,  inclosed  within  a  bracket,  signifies  that  the  whole  of  the  latter  are 
to  be  multiplied  by  that  number.  Occasionally  the  bracket  is  omitted,  when 
the  number  affects  all  the  symbols  between  itself  and  the  next  sign.  A  few 
examples  will  serve  to  illustrate  these  several  points. 

Sulphate  of  soda  NaO  +  SO3  ,  or  NaO  ,  SO3 
Nitrate  of  potassa  KO  -j-  NOg  ,  or  KO  ,  NO5 

The  base  being  always  placed  first. 

Double  sulphate  of  copper  and  potassa  CuO  ,  SOg-f-KO  ,  SO, 

The  same  in  a  crystallized  state CuO  ,  SOg-fKO  ,  SOg-j-BHO 

Common  crystallized  alum,  or  double  sulphate  of  alumina  and  potassa,  is 
thus  written  :  — 

AI2O3  ,  SSOg-fKO  ,  SO3+24HO 

In  expressing  organic  compounds,  where  three  or  more  elements  exist,  the 
^amo  plan  is  used. 

Sngar  CijHiiO,, 

Alcohol CXO2 

Acetic  acid HO  ,  C4H3O3 

Morphine Cg^HjgN  Og 

Acetate  of  morphine Cg^HjgN  Og  ,  C^H^O, 

Acetate  of  soda NaO  ,  C.H„0, 

16  '     4    8   s 


182  GENERALPRINCIPLESOF 

By  such  a  system,  the  eye  is  enabled  to  embrace  the  whole  at  a  glance, 
and  gain  a  distinct  idea  of  the  composition  of  the  body,  and  its  relations  to 
others  similarly  described. 


//• 


Some  authors  are  in  the  habit  of  making  use  of  contractions,  which,  how- 
ever, are  by  no  means  generally  adopted.  Thus,  two  equivalents  of  a  sub- 
stance are  indicated  by  the  symbol  with  a  short  line  drawn  through  or  below 
it ;  an  equivalent  of  oxygen  is  signified  by  a  dot,  and  one  of  sulphur  by  a 
comma.  These  alterations  are  sometimes  convenient  for  abbreviating  a  long 
formula,  but  easily  liable  to  mistakes.     Thus, 

Sesquioxide  of  iron  FeO',  or  F  eO%  or  Fe,  instead  of  Fcj  Oj 

Bisulphide  of  carbon  C,  instead  of  CSa 

Crystallized  alum  as  before  AlSg-f  KS-f-24H. 

THE   ATOMIC    THEORY. 

That  no  attempt  should  have  been  made  to  explain  the  reason  of  the  very 
remarkable  manner  in  which  combination  occurs  in  the  production  of  che- 
mical compounds,  and  to  point  out  the  nature  of  the  relations  between  the 
different  modifications  of  matter  which  fix  and  determine  these  peculiar  and 
definite  changes,  would  have  been  unlikely,  and  in  contradiction  with  the 
speculative  tendency  of  the  human  mind.  Such  an  attempt,  and  a  very  inge- 
nious and  successful  one  it  is,  has  been  made,  namely,  the  atomic  hypothesis 
of  Dr.  Dal  ton. 

From  very  ancient  times,  the  question  of  the  constitution  of  matter  with, 
respect  to  divisibility  has  been  debated,  some  adopting  the  opinion  that  this 
divisibility  is  infinite,  and  others,  that  when  the  particles  become  reduced  to 
a  certain  degree  of  tenuity,  far  indeed  beyond  any  state  that  can  be  reached 
by  mechanical  means,  they  cease  to  be  farther  diminished  in  magnitude  ; 
they  become,  in  short,  aioms.'^  Now,  however  the  imagination  may  succeed 
in  figuring  to  itself  the  condition  of  matter  on  either  view,  it  is  hardly  neces- 
sary to  mention  that  we  have  absolutely  no  means  at  our  disposal  for  deciding 
such  a  question,  which  remains  at  the  present  day  in  the  same  state  as  when 
it  first  engaged  the  attention  of  the  Greek  philosophers,  or  perhaps  that  of 
the  sages  of  Egypt  and  Hindostan  long  before  them. 

Dr.  Dalton's  hypothesis  sets  out  by  assuming  the  existence  of  such  atoms 
or  indivisible  particles,  and  states,  that  compounds  are  formed  by  the  union 
of  atoms  of  different  bodies,  one  to  one,  one  to  two,  &c.  The  compound  atom 
joins  itself  in  the  same  manner  to  a  compound  atom  of  another  kind,  and  a 
combination  of  the  second  order  results.  Let  it  be  granted,  farther,  that  the 
relative  weights  of  the  atoms  are  in  the  proportions  of  the  equivalent  numbers, 
and  the  hypothesis  becomes  capable  of  rendering  consistent  and  satisfactory 
reasons  for  all  the  consequences  of  those  beautiful  laws  of  combination  lately 
discussed. 

Chemical  compounds  must  always  be  definite ;  they  must  always  contain 
the  same  number  of  atoms,  of  the  same  kind,  arranged  in  a  similar  manner. 
The  same  kind  and  number  of  atoms  need  not,  however,  of  necessity  produce 
the  same  substance,  for  they  may  be  differently  arranged ;  and  much  depends 
upon  this  circumstance. 

Again,  the  law  of  multiple  proportions  is  perfectly  well  explained ;  an  atora 


*  "Aro/toj,  that  which  cannot  be  cut. 


CHEMICAL     PHILOSOPHY.  183 

of  nitrogen  unites  with  one  of  oxygen  to  form  laughing  gas ;  with  two,  to 
form  binoxide  of  nitrogen ;  with  three,  to  produce  nitrous  acid ;  with  four, 
hvponitric  acid ;  and  with  five,  nitric  acid, — perhaps  something  after  the 
manner  represented  in  fig.  124,  in  which  the  circle  with  a  cross  represents 
*Jie  atom  of  nitrogen,  and  the  plain  circle  that  of  oxygen. 

Fig.  124. 


©OC^O 


Two  atoms  of  one  substance  may  unite  themselves  with  three  or  even  with 
seven  of  another,  as  in  the  case  of  one  of  the  acids  of  manganese ;  but  such 
combinations  are  rare./' 

The  mode  in  which  bodies  replace,  or  may  be  substituted  for,  each  other, 
is  also  perfectly  intelligible,  as  a  little  consideration  will  show. 

Finally,  the  law  which  fixes  the  equivalent  of  a  compound  at  the  sum  of 
the  equivalents  of  the  components,  receives  an  equally  satisfactory  expla- 
nation. 

The  difiiculties  in  the  general  application  of  the  atomic  hypothesis  are 
chiefly  felt  in  attempting  to  establish  some  wide  and  universal  relation  be- 
tween combining  number  and  combining  volume,  among  gases  and  vapours, 
and  in  the  case  of  the  highly  complex  products  of  organic  chemistry.  These 
obstacles  have  grown  up  in  comparatively  recent  times.  On  the  other  hand, 
the  remarkable  observations  of  the  specific  capacities  for  heat  of  equivalent 
quantities  of  the  solid  elementary  substances,  might  be  urged  in  favour  of 
tills  or  some  similar  molecular  hypothesis.  But  even  here  serious  discrep- 
ancies exist ;  we  may  not  take  liberties  with  equivalent  numbers  determined 
by  exact  chemical  research,  and,  in  addition,  a  simple  relation  is  generally 
found  to  be  wanting  between  the  capacity  for  heat  of  the  compound  and  that 
of  its  elements. 

The  theory  in  question  has  rendered  great  service  to  chemical  science ;  it 
has  excited  a  vast  amount  of  inquiry  and  investigation,  which  have  contribu- 
ted very  largely  to  define  and  fix  the  laws  of  combination  themselves.  In 
more  recent  days  it  is  not  impossible,  that,  without  some  such  hypothetical 
guide,  the  exquisitely  beautiful  relations  which  Mitscherlich  and  others  have 
shown  to  exist  between  crystalline  form  and  chemical  composition,  might 
never  have  been  brought  to  light,  or,  at  any  rate,  their  discovery  might 
have  been  greatly  delayed.  At  the  same  time,  it  is  indispensable  to  draw 
the  broadest  possible  line  of  distinction  between  this,  which  is  at  the  best 
but  a  graceful,  ingenious,  and,  in  its  place,  useful  hypothesis,  and  those 
great  general  laws  of  chemical  action  which  are  the  pure  and  unmixed  result 
of  inductive  research.* 


Chemical  Affinity. 

The  term  chemical  affinity,  or  chemical  attraction,  has  been  invented  to 
describe  that  particular  power  or  force,  in  virtue  of  which,  union,  often  of  a 
very  intimate   and  permanent  nature,  takes  place  between   two   or  more 

*  The  expression  atomic  weight  is  very  often  substituted  for  that  of  equivalent  weight,  and 
is,  in  fact,  in  almost  every  case  to  be  understood  as  such :  it  is,  ->fti-haps,  better  avoided. 


184  GENERAL    PRINCIPLES    OF 

bodies,  in  such  a  way  as  to  give  rise  to  a  neio  substance,  having,  for  the  most 
part,  propei'ties  completely  in  discordance  with  those  of  its  components. 

The  attraction  thus  exerted  between  diflFerent  kinds  of  matter  is  to*  be  dis- 
tinguished from  other  modifications  of  attractive  force  which  arc  exerted 
indiscriminately  between  all  descriptions  of  substances,  sometimes  at  enor- 
mous distances,  and  sometimes  at  intervals  quite  inappreciable.  Examples 
of  the  latter  are  to  be  seen  in  cases  of  what  is  called  cohesion,  when  the  par- 
ticles of  solid  bodies  are  immovably  bound  together  into  a  mass.  Then 
there  are  other  effects  of,  if  possible,  a  still  more  obscure  kind  ;  such  as  the 
various  actions  of  surface,  the  adhesion  of  certain  liquids  to  glass,  the  re- 
pulsion of  others,  the  ascent  of  water  in  narrow  tubes,  and  a  multitude  of 
curious  phenomena  which  are  described  in  works  on  Natural  Philosophy, 
under  the  head  of  molecular,  actions.  From  all  these,  true  chemical  attraction 
may  be  at  once  distinguished  by  the  deep  and  complete  change  of  characters 
which  follows  its  exertion ;  we  might  define  aflinity  to  be  a  force  by  which 
new  substances  are  generated. 

It  seems  to  be  a  general  law  that  bodies  most  opposed  to  each  other  in 
chemical  properties  evince  the  greatest  tendency  to  enter  into  combination, 
and,  conversely,  bodies  between  which  strong  analogies  and  resemblances 
can  be  traced,  manifest  a  much  smaller  amount  of  mutual  attraction.  For 
example,  hydrogen  and  the  metals  tend  very  strongly  indeed  to  combine  with 
oxygen,  chlorine,  and  iodine ;  the  attraction  between  the  different  members 
of  these  two  groups  is  incomparably  more  feeble.  Sulphur  and  phosphorus 
stand,  as  it  were,  mid-way ;  they  combine  with  substances  of  one  and  the 
other  class,  their  properties  separating  them  sufficiently  from  both.  Acids 
are  drawn  towards  alkalis,  and  alkalis  towards  acids,  while  union  among 
themselves  rarely,  if  ever,  takes  place. 

Nevertheless,  chemical  combination  graduates  so  imperceptibly  into  mere 
mechanical  mixture,  that  it  is  often  impossible  to  mark  the  limit.  Solution 
is  the  result  of  a  weak  kind  of  affinity  existing  between  the  substance  dis- 
solved and  the  solvent ;  an  affinity  so  feeble  as  completely  to  lose  one  of  its 
most  prominent  features  when  in  a  more  exalted  condition,  namely,  power  of 
causing  elevation  of  temperature ;  for  in  the  act  of  mere  solution  the  tem- 
perature falls,  the  heat  of  combination  being  lost  and  overpowered  by  the 
effects  of  change  of  state. 

The  force  of  chemical  attraction  thus  varies  greatly  with  the  nature  of 
the  substances  between  which  it  is  exerted ;  it  is  influenced,  moreover,  to  a 
very  large  extent  by  external  or  adventitious  circumstances.  An  idea  for- 
merly prevailed  that  the  relations  of  affinity  were  fixed  and  constant  between 
the  same  substances,  and  great  pains  were  taken  in  the  preparation  of  tables 
exhibiting  what  was  called  the  precedence  of  affinities.  The  order  pointed 
out  in  these  lists  is  now  acknowledged  to  represent  the  order  of  precedence 
for  the  circumstances  under  which  the  experiments  were  made,  but  nothing 
more ;  so  soon  as  these  circumstances  become  changed,  the  order  is  disturbed. 
The  ultimate  effect,  indeed,  is  not  the  result  of  the  exercise  of  one  single 
force,  but  rather  the  joint  effect  of  a  number,  so  complicated  and  so  variable 
in  intensity,  that  it  is  but  seldom  possible  to  predict  the  consequences  of  any 
yet  untried  experiment.  The  following  may  serve  as  examples  of  the  tables 
alluded  to ;  the  first  illustrates  the  relative  affinities  of  a  number  of  bases 
for  sulphuric  acid,  each  decomposing  the  combination  of  the  acid  with  the 
base  below  it ;  thus,  magnesia  decomposes  sulphate  of  ammonia ;  lime  dis- 
places the  acid  from  sulphate  of  magnesia,  &c.  The  salts  are  supposed  to 
be  dissolved  in  water.  The  second  table  exhibits  the  order  of  affinity  for 
oxygen  of  several  metals,  mercury  reducing  a  solution  of  silver,  coppsr  one 
of  mercury,  &c. 


CHEMICAL    PHILOSOPHY.  185 


Sulphuric  acid. 
Baryta,  Lime, 

etrontia,  Magnesia, 

Potassa,  Ammonia. 

Soda, 


Oxygen. 
Zinc,  Mercury, 

Lead,  Silver. 

Copper, 


It  will  be  proper  to  examine  shortly  some  of  these  extraneous  causes  to 
which  allusion  has  been  made,  which  modify  to  so  great  an  extent  the  direct 
and  original  effects  of  the  specific  attractive  force. 

Alteration  of  temperature  may  be  reckoned  among  these.  When  metallic 
mercui-y  is  heated  nearly  to  its  boiling  point,  and  in  that  state  exposed  for  a 
lengthened  period  to  the  air,  it  absorbs  oxygen,  and  becomes  converted  into 
a  dark  red  crystalline  powder.  This  very  same  substance,  when  raised  to 
a  still  higher  temperature,  spontaneously  separates  into  metallic  mercury 
and  oxygen  gas.  It  may  be  said,  and  probably  with  truth,  that  the  latter 
change  is  greatly  aided  by  the  tendency  of  the  metal  to  assume  the  vaporous 
state ;  but,  precisely  the  same  fact  is  observed  with  another  metal,  palladium, 
which  is  not  volatile  at  all,  but  which  oxidates  superficially  at  a  red-heat, 
and  again  becomes  reduced  when  the  tempei*ature  rises  to  whiteness. 

Insolubility  and  the  power  of  vaporization  are  perhaps,  beyond  all  other 
disturbing  causes,  the  most  potent ;  they  interfere  in  almost  every  reaction 
which  takes  place,  and  very  frequently  turn  the  scale  when  the  opposed  forces 
do  not  greatly  differ  in  energy.  It  is  easy  to  give  examples.  When  a  solu- 
tion of  lime  in  hydrochloric  acid  is  mixed  with  a  solution  of  carbonate  of 
ammonia,  double  interchange  ensues,  carbonate  of  lime  and  hydrochlorate 
of  ammonia  being  generated.  Here  the  action  can  be  shown  to  be  in  a  great 
measure  determined  by  the  insolubility  of  the  carbonate  of  lime.  Again, 
dry  carbonate  of  lime,  powdered  and  mixed  with  hydrochlorate  of  ammonia, 
and  the  whole  heated  in  a  retort,  gives  a  sublimate  of  carbonate  of  ammonia, 
while  chloride  of  calcium  remains  behind.  In  this  instance,  it  is  no  doubt 
the  great  volatility  of  the  ammoniacal  salt  which  chiefly  determines  the  kind 
of  decomposition. 

When  iron-filings  are  heated  to  redness  in  a  porcelain  tube,  and  vapour  of 
water  passed  over  them,  the  water  undergoes  decomposition  with  the  utmost 
facility,  hydrogen  is  rapidly  disengaged,  and  the  iron  converted  into  oxide. 
On  the  other  hand,  oxide  of  iron  heated  in  a  tube  through  which  a  stream 
of  dry  hydrogen  is  passed,  suffers  almost  instantaneous  reduction  to  the 
metallic  state,  while  the  vapour  of  water,  carried  forward  by  the  current  of 
gas,  escapes  as  a  jet  of  steam  from  the  extremity  of  the  tube.  In  these 
experiments,  the  affinities  between  the  iron  and  oxygen,  and  the  hydrogen 
and  oxygen,  are  so  nearly  balanced,  that  the  difference  of  atmosphere  is  suf- 
ficient to  settle  the  point.  An  atmosphere  of  steam  offers  little  resistance 
to  the  escape  of  hydrogen ;  one  of  hydrogen  bears  the  same  relation  to  steam ; 
and  this  apparently  trifling  difference  of  circumstances  is  quite  enough  for 
the  purpose. 

The  decomposition  of  vapour  of  water  by  white-hot  platinum,  pointed  out 
by  Mr.  Grove,  will  probably  be  referred  in  great  part  to  this  influence  of 
atmosphere,  the  steam  offering  great  facilities  for  tiie  assumption  of  the 
elastic  condition  by  the  oxygen  and  hydrogen.  The  decomposition  ceases 
as  soon  as  these  gases  amount  to  about  l-3000th  of  the  bulk  of  the  mixture, 
and  can  only  be  renewed  by  their  withdrawal.  The  attraction  of  uxygeu 
for  hydrogen  is  probably  much  weakened  by  the  very  high  temperature.  The 
recombination  of  the  gases  by  the  heated  metal  is  rendered  impossible  by 
their  state  of  dilution. 

What  is  called  the  nascent  state  is  one  very  favourable  to  chemical  com- 
Dination.  Thus  carbon  and  nitrogen  refuse  to  combine  w'th  gaseous  hy- 
16* 


186      PRINCIPLES     OF     CHEMICAL     PHILOSOPHY. 

drogen ;  yet  when  these  substances  are  simultaneously  liberated  from  some 
previous  combination,  they  unite  with  great  ease,  as  when  organic  matters 
are  destroyed  by  heat,  or  by  spontaneous  putrefactive  change.  There  is  a 
strange  and  extraordinary,  and  at  the  same  time  very  extensive  class  of 
actions,  grouped  together  under  the  general  title  of  cases  of  disposing  affin- 
ity. The  preparation  of  hydrogen  from  zinc  and  sulphuric  acid  is  one  of 
the  most  familiar.  A  piece  of  polished  zinc  or  iron,  put  into  pure  water, 
manifests  no  power  of  decomposing  the  latter  to  the  smallest  extent;  it 
remains  perfectly  bright  for  any  length  of  time.  On  the  addition,  however, 
of  a  little  sulphuric  acid,  hydrogen  is  at  once  freely  disengaged,  and  the 
metal  becomes  oxidized  and  dissolved.  Now,  the  only  intelligible  function 
of  the  acid  is  to  dissolve  oflF  the  oxide  as  fast  as  it  is  produced ;  but  why  is 
the  oxide  produced  when  acid  is  present,  and  not  otherwise  ?  The  question 
is  very  difficult  to  answer. 

Great  numbers  of  examples  of  this  curious  indirect  action  might  be 
adduced.  Metallic  silver  does  not  oxidize  at  any  temperature ;  nay  more, 
its  oxide  is  easily  decomposed  by  simple  heat ;  yet  if  the  finely-divided  metal 
be  mixed  with  siliceous  matter  and  alkali,  and  ignited,  the  whole  fuses  to  a 
yellow  transparent  glass  or  silicate  of  silver.  Platinum  is  attacked  by  fused 
hydrate  of  potassa;  hydrogen  is  probably  disengaged  while  the  metal  is 
oxidized ;  this  is  an  effect  which  never  happens  to  silver  under  the  same  cir- 
cumstances, although  silver  is  a  much  more  oxidable  substance  than  plati- 
num. The  fact  is,  that  potassa  forms  with  the  oxide  of  the  last-named 
metal  a  kind  of  saline  combination,  in  which  the  oxide  of  platinum  acts  as 
an  acid ;  and  hence  its  formation  under  the  disposing  influence  of  the  power- 
ful base. 

In  the  remarkable  decomposition  suffered  by  various  organic  bodies  when 
heated  in  contact  with  caustic  alkali  or  lime,  we  have  other  examples  of  the 
same  fact.  Products  are  generated  which  are  never  formed  in  the  absence 
of  the  base ;  the  reaction  is  invariably  less  complicated,  and  its  results  fewer 
in  number  and  more  definite,  than  in  the  event  of  simple  destruction  by  a 
graduated  heat.  The  preparation  of  light  carbonetted  hydrogen  by  the  new 
artificial  process,  already  described,  is  an  excellent  example. 

There  is  yet  a  still  more  obscure  class  of  phenomena,  in  which  effects  are 
brought  about  by  the  mQYQ  presence  of  a  substance,  which  itself  undergoes 
no  change  whatever ;  the  experiment  mentioned  in  the  article  on  oxygen, 
in  which  that  gas  is  obtained,  with  the  greatest  facility,  by  heating  a  mix- 
ture of  chlorate  of  potassa  and  binoxide  of  manganese,  is  an  excellent  case 
in  point.  The  salt  is  decomposed  at  a  very  far  lower  temperature  than 
would  otherwise  be  required.  The  oxide  of  manganese,  however,  is  not  in 
the  slightest  degree  altered ;  it  is  found,  after  the  experiment,  in  the  same 
state  as  before.  The  name  katalysis  is  sometimes  given  to  these  peculiar 
actions  of  contact ;  the  expression  is  not  significant,  and  may  be  for  that 
reason  the  more  admissible,  as  it  suggests  no  explanation. 

It  is  proper  to  remark,  that  the  contact-decompositions  alluded  to  are 
sometimes  mixed  up  with  other  effects,  which  are,  in  reality,  much  more  in- 
telligible, as  the  action  of  finely-divided  platinum  upon  certain  gaseous  mix- 
tures, in  which  the  solid  really  seems  to  have  the  power  of  condensing  the 
gas  upon  its  greatly  extended  surface,  and  thereby  inducing  combination  by 
liriuging  the  particles  within  the  sphere  of  their  mutual  attractions. 


CHEMISTRY    OF    THE    VOLTAIC    PILE.  1^  T 


ELECTRO-CHEMICAL  DECOMPOSITION;  CHEMISTRY  OF  THE 
VOLTAIC  PILE. 


When  a  voltaic  current  of  considerable  power  is  made  to  traverse  various 
compound  liquids,  a  separation  of  the  elements  of  these  liquids  ensues ;  pro- 
vided that  the  liquid  be  capable  of  conducting  a  current  of  a  certain  degree 
of  energy,  its  decomposition  almost  always  follows. 

The  elements  are  disengaged  solely  at  the  limiting  surfaces  of  the  liquid; 
where,  according  to  the  common  mode  of  speech,  the  current  enters  and 
leaves  the  latter,  all  the  intermediate  portions  appearing  perfectly  quiescent. 
In  addition,  the  elements  are  not  separated  indifferently  and  at  random  at 
these  two  surfaces,  but,  on  the  contrary,  make  their  appearance  with  per- 
fect uniformity  and  constancy  at  one  or  the  other,  according  to  their  che- 
mical character,  namely,  oxygen,  chlorine,  iodine,  acids,  &c.,  at  the  surface 
connected  with  the  copper  or  positive  end  of  the  battery ;  hydrogen,  the 
metals,  &c.,  at  the  surface  in  connection  with  the  zinc  or  negative  extremity 
of  the  arrangement. 

The  termination  of  the  battery  itself,  usually,  but  by  no  means  necessa-* 
rily,  of  metal,  are  designated  poles  or  electrodes,^  as  by  their  intervention 
the  liquid  to  be  experimented  on  is  made  a  part  of  the  circuit.  The  process 
of  decomposition  by  the  current  is  called  electrolysis,^  and  the  liquids,  which, 
when  thus  treated,  yield  up  their  elements,  are  denominated  electrolytes. 

When  a  pair  of  platinum  plates  are  plunged  into  a  glass  of  water  to  which 
a  few  drops  of  oil  of  vitriol  have  been  added,  and  the  plates  connected  by 
wires  with  the  extremities  of  an  active  battery,  oxygen  is  disengaged  at  the 
positive  electrode,  and  hydrogen  at  the  negative,  in  the  proportion  of  one 
measure  of  the  former  to  two  of  the  latter  nearly.  This  experiment  has 
before  been  described.^ 

A  solution  of  hydrochloric  acid  mixed  with  a  little  Saxon  blue  (indigo), 
and  treated  in  the  same  manner,  yields  hydrogen  on  the  negative  side,  and 
chlorine  on  the  positive,  the  indigo  there  becoming  bleached. 

Iodide  of  potassium  dissolved  in  water  is  decomposed  in  a  similar  man- 
ner, and  with  still  greater  ease ;  the  free  iodine  at  the  positive  side  can  be 
recognized  by  its  brown  colour,  or  by  the  addition  of  a  little  gelatinous 
starch. 

Every  liquid  is  not  an  electrolyte ;  many  refuse  to  conduct,  and  no  decom- 
position can  then  occur ;  alcohol,  ether,  numerous  essential  oils,  and  other 
products  of  organic  chemistry,  besides  a  few  saline  inorganic  compounds,  act 
in  this  manner,  and  completely  arrest  the  current  of  a  very  powerful  battery. 
It  is  a  very  curious  fact,  and  well  deserves  attention,  that  very  nearly,  if  not 
all  the  substances  acknowledged  to  be  susceptible  of  electrolytic  decomposi- 
tion, belong  to  one  class;  they  are  all  binary  compounds,  containing  single 

*  From  i^\tKTpov,  and  i^df,  a  way. 

•  From  fi^tKTpov,  and  Auw,  I  loose. 
»  Page  115. 


1?<8  ELECTRO-CHEMICAL     DECOMPORITTONj 

equivalents  of  their  components,  the  latter  being  strongly  opposed  to  «ach 
other  in  their  chemical  relations,  and  held  together  by  very  powerful  affinities. 

The  amount  of  power  required  to  eflfect  decomposition  varies  greatly; 
solution  of  iodide  of  potassium,  melted  chloride  of  lead,  solution  of  hydro- 
chloric acid,  water  mixed  with  a  little  oil  of  vitriol,  and  pure  water,  demand 
in  this  respect  very  different  degrees  of  electrical  force,  the  resistaftce  to 
decomposition  increasing  from  the  first-mentioned  substance  to  the  last. 

One  of  the  most  important  and  indispensable  conditions  of  electrolysis  is 
fluidity ;  bodies  which  when  reduced  to  the  liquid  condition  freely  conduct 
and  as  freely  suffer  decomposition,  become  absolute  insulators  to  the  elec- 
tricity of  the  battery  when  they  become  solid.  Chloride  of  lead  offers  a  good 
illustration  of  this  fact ;  when  fused  in  a  little  porcelain  crucible  it  gives  up 
its  elements  with  the  utmost  ease,  and  a  galvanometer,  interposed  somewhere 
in  the  circuit,  is  strongly  affected.  But  when  the  source  of  heat  is  withdrawn, 
and  the  salt  suffered  to  solidify,  all  signs  of  decomposition  cease,  and  at  the 
Bame  moment  the  magnetic  needle  reassumes  its  natural  position.  In  the 
Bame  manner  the  thinnest  film  of  ice  completely  arrests  the  current  of  a  pow- 
erful voltaic  apparatus ;  the  instant  the  ice  is  liquefied  at  any  one  point,  so 
that  water-communication  may  be  restored  between  the  electrodes,  the  cur- 
rent again  passes,  and  decomposition  occurs.  Fusion  by  heat,  and  solution 
In  aqueous  liquids,  answer  the  purpose  equally  well.  A  fluid  substance  may 
conduct  a  strong  current  of  electricity  without  being  decomposed ;  there  are 
a  few  examples  already  known ;  the  electrolysis  of  a  solid  is,  from  its  physi- 
cal properties,  of  course  out  of  the  question. 

Liquids  often  exhibit  the  property  of  conduction  for  currents  strong  enough 
to  be  indicated  by  the  galvanometer,  but  yet  incapable  of  causing  decompo- 
sition in  the  manner  described.  These  currents  may  be  conveyed  through 
extensive  masses  of  liquids ;  the  latter  seem,  under  these  circumstances,  to 
conduct  after  the  manner  of  metals,  without  perceptible  molecular  change. 

The  metallic  terminations  of  the  battery,  the  poles  or  electrodes,  have,  in 
themselves,  nothing  in  the  shape  of  attractive  or  repulsive  power  for  the 
elements  so  often  separated  at  their  surfaces.  Finely-divided  metal  suspended 
in  water,  or  chlorine  held  in  solution  in  that  liquid,  shows  not  the  least 
symptom  of  a  tendency  to  accumulate  around  them ;  a  single  element  is  alto- 
gether unaffected,  directly  at  least ;  severance  from  that  previous  combination 
is  required,  in  order  that  this  appearance  should  be  exhibited. 

It  is  necessary  to  examine  the  process  of  electrolysis  a  little  more  closely. 
When  a  portion  of  water,  for  example,  is  subjected  to  decomposition  in  a 
glass  vessel  with  parallel  sides,  oxygen  is  disengaged  at  the  positive  electrode, 
and  hydrogen  at  the  negative  ;  the  gases  are  perfectly  pure  and  unmixed. 
If,  while  the  decomposition  is  rapidly  proceeding,  the  intervening  water  be 
examined  by  a  beam  of  light,  or  by  other  means,  not  the  slightest  disturbance 
or  movement  of  any  kind  will  be  perceived,  nothing  like  currents  in  the  liquid 
or  bodily  transfer  of  gas  from  one  part  to  another  can  be  detected,  and  yet 
two  portions  of  water,  separated  perhaps  by  an  interval  of  four  or  five  inches, 
may  be  respectively  evolving  pure  oxygen  and  pure  hydrogen. 

There  is,  it  would  seem,  but  one  mode  of  explaining  this  and  all  similar 
cases  of  regular  electrolytic  decomposition ;  this  is  by  assuming  that  all  the 
particles  of  water  between  the  electrodes,  and  by  which  the  current  is  con- 
veyed, simultaneously  suffer  decomposition,  the  hydrogen  travelling  in  one 
direction  and  the  oxygen  in  the  other.  The  neighbouring  elements,  thus 
brought  into  close  proximity,  unite  and  reproduce  water,  again  destined  to 
be  decomposed  by  a  repetition  of  the  same  change.  In  this  manner  each 
particle  of  hydrogen  may  be  made  to  travel  in  one  direction,  by  becoming 
successively  united  to  each  particle  of  oxygen  between  itself  and  the  negative 
electrode ;  when  it  reaches  the  latter,  finding  no  disengaged  particle  of  oxygen 


CHEMISTRY    OF     THE    VOLTAIC    PILE. 


189 


for  its  reception,  it  is  rejected  as  it  were  from  the  series,  and  thrown  oflF  in 
a  separate  state.  The  same  thing  happens  to  each  particle  of  oxygen,  which 
at  the  same  time  passes  continually  in  the  opposite  direction,  by  combining 
successively  with  each  particle  of  hydrogen  that  moment  separated,  with 
which  it  meets,  until  at  length  it  arrives  at  the  positive  plate  or  wire,  and  is 
disengaged.  A  succession  of  particles  of  hydrogen  are  thus  continually 
thrown  off  from  the  decomposing  mass  at  one  extremity,  and  a  corresponding 
succession  of  particles  of  oxygen  at  the  other.  The  power  of  the  current  is 
exerted  with  equal  energy  in  every  part  of  the  liquid  conductor,  although  its 
effects  only  become  manifest  at  the  very  extremities.     The  action  is  one  of  a 

Fig.  125. 


.©1©1®1©M®1® 


Water  in  usual  state. 

purely  molecular  or  internal  nature,  and  the  metal  terminations  of  the  bat- 
tery merely  serve  the  purpose  of  completing  the  connection  between  the 
latter  and  the  liquid  to  be  decomposed.  The  figures  125  and  126  are  intended 
to  assist  the  imagination  of  the  reader,  who  must  at  the  same  time  avoid  re- 
garding them  in  any  other  light  than  that  of  a  somewhat  figurative  mode  of 
representing  the  curious  phenomena  described.  The  circles  are  intended  to 
indicate  the  elements,  and  are  distinguished  by  their  respective  symbols. 


© 


Fig.  126. 


©, 


© 


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Water  undergoing  electrolysis. 

A  distinction  is  to  be  carefully  drawn  between  true  and  regular  electro- 
lysis, and  what  is  called  secondary  decomposition,  brought  about  by  the 
reaction  of  the  bodies  so  eliminated  upon  the  surrounding  fluid,  or  upon  the 
substance  of  the  electrodes ;  hence  the  advantage  of  platinum  for  the  latter 
purpose  when  electrolytic  actions  are  to  be  studied  in  their  greatest  sim- 
plicity, that  metal  being  scarcely  attacked  by  any  ordinary  agents.  When, 
for  example,  a  solution  of  nitrate  or  acetate  of  lead  is  decomposed  by  the 
current  between  platinum  plates,  metallic  lead  is  deposited  at  the  negative 
side,  and  a  brown  powder,  binoxide  of  lead,  at  the  positive :  the  latter  sub- 
stance is  the  result  of  a  secondary  action ;  it  proceeds,  in  fact,  from  the 
nascent  oxygen  at  the  moment  of  its  liberation  reacting  upon  the  protoxide 
of  lead  present  in  the  salt,  and  converting  it  into  binoxide,  which  is  insoluble 
in  the  dilute  acid.  There  is  every  reason  to  believe  that  when  sulphurio 
and  nitric  acids  seem  to  be  decomposed  by  the  current,  the  effect  is  really 
due  to  the  water  they  contain  becoming  decomposed,  and  reacting  by  its 
hydrogen  upon  the  acid ;  for  these  bodies  do  not  belong  to  the  class  of  elec- 
trolytes, as  already  specified,  and  would  probably  refuse  to  conduct  could 
they  be  examined  in  an  anhydrous  condition. 

If  a  number  of  different  electrolytes,  such  as  acidulated  water,  siJphate 
of  copper,  iodide  of  potassium,  fused  chloride  of  lead,  &c.,  be  arranged  in  ft 


19) 


ELECTRO-CHEMICAL    DECOMPOSITION; 


Fig.  127. 


series,  And  the  same  current  be  made  to  traverse  the  whole,  all  will  suffer 
decomposition  at  the  same  time,  but  by  no  means  to  the  same  amount.  If 
arrangements  be  made  by  -which  the  quantities  of  the  eliminated  elements 
can  be  accurately  ascertained,  it  will  be  found,  when  the  decomposition  has 
proceeded  to  some  extent,  that  these  latter  will  have  been  disengaged  exactly 
in  the  ratio  of  the  chemical  equivalents.  The  same  current  which  decomposes 
9  parts  of  water  will  separate  into  their  elements  166  parts  of  iodide  of  po- 
tassium, 139-2  parts  of  chloride  of  lead,  &c.  Hence  the  very  important 
conclusion :  The  action  of  the  current  is  perfectly  definite  in  its  nature,  pro- 
ducing a  fixed  and  constant  amount  of  decomposition,  expressed  in  each 
electrolyte  by  the  value  of  its  chemical  equivalent. 

From  a  very  extended  series  of  experiments,  based  on  this  and  other  me- 
thods of  research,  Mr.  Faraday  was  enabled  to  draw  the  general  inference  that 
eflfects  of  chemical  decomposition  were  always  proportionate  to  the  quantity 
of  circulating  electricity,  and  might  be  taken  as  an  accurate  and  trustworthy 
measure  of  the  latter.  Guided  by  this  highly 
important  principle,  he  constructed  his  voltame- 
ter, an  instrument  which  has  rendered  the  great- 
est service  to  electrical  science.  This  is  merely 
an  arrangement  by  which  a  little  acidulated 
water  is  decomposed  by  the  current,  the  gas 
evolved  being  collected  and  measured.  By  plac- 
ing such  an  instrument  in  any  part  of  the  circuit, 
the  quantity  of  electric  force  necessary  to  pro- 
duce any  given  effect  can  be  at  once  estimated ; 
or,  on  the  other  hand,  any  required  amount  of 
the  latter  can  be,  as  it  were,  measured  out  and 
adjusted  to  the  object  in  view.  The  voltameter 
has  received  many  different  forms ;  one  of  the 
most  extensively  useful  is  that  shown  in  fig.  127, 
in  which  the  platinum  plates  are  separated  by  a 
very  small  interval,  and  the  gas  is  collected  in  a  graduated  jar  standing  on 
the  shelf  of  the  pneumatic  trough,  the  tube  of  the  instrument,  which  is  filled 
to  the  neck  with  dilute  sulphuric  acid,  being  passed  beneath  the  jar. 

The  decompositions  of  the  voltaic  battery  can  be  effected  by  the  electricity 
of  the  common  machine,  by  that  developed  by  magnetic  action,  and  by  that 
of  animal  origin,  but  to  an  extent  incomparably  more  minute.  This  arises 
from  the  very  small  qua?itity  of  electricity  set  in  motion  by  the  machine, 
although  its  tension,  that  is,  power  of  overcoming  obstacles,  and  passing 
through  imperfect  conductors,  is  exceedingly  great.  A  pair  of  small  wires 
of  zinc  and  platinum,  dipping  into  a  single  drop  of  dilute  acid,  develope  far 
more  electricity,  to  judge  from  the  chemical  effects  of  such  an  arrangement, 
than  very  many  turns  of  a  large  plate  electrical  machine  in  high  action 
Nevertheless,  polar  or  electrolytic  decomposition  can  be  distinctly  and  satis- 
factorily effected  by  the  latter,  although  on  a  minute  scale. 

With  a  knowledge  of  the  principles  laid  down,  the  study  of  the  voltaic 
battery  may  be  resumed  and  completed.  In  the  first  place,  two  very  different 
views  have  been  held  concerning  the  source  of  the  electrical  disturbance  in 
that  apparatus.  Volta  himself  ascribed  it  to  mere  contact  of  dissimilar 
metals ;  to  what  was  denominated  an  electro-motive  force,  called  into  being 
by  such  contact ;  the  liquid  merely  serving  the  purpose  of  a  conductor  be- 
tween one  pair  of  metals  and  that  succeeding.  Proof  was  supposed  to  be 
given  of  the  fundamental  position  by  an  experiment  in  which  discs  of  zino 
and  copper  attached  to  insulating  handles,  after  being  brought  into  close 
contact,  were  found,  by  the  aid  of  a  very  delicate  gold-leaf  electroscope,  to 
be  in  opposite  electrical  states.    It  appears,  however,  that  the  more  carefully 


CHEMISTEY    OF    THE    VOLTAIC    PILE.  191 

this  experiment  is  made,  the  smaller  is  the  eflFect  observed ;  and  hence  it  is 
judged  highly  probable  that  the  whole  may  be  due  to  accidental  causes, 
against  which  it  is  almost  impossible  to  guard. 

On  the  other  hand,  the  observation  was  soon  made  that  the  power  of  the 
battery  always  bore  some  kind  of  proportion  to  the  chemical  action  upon  the 
zinc ;  that,  for  instance,  when  pure  water  was  used  the  effect  was  extremely 
feeble ;  with  a  solution  of  salt,  it  became  much  greater ;  and,  lastly,  with 
dilute  acid,  greatest  of  all ;  so  that  some  relation  evidently  existed  between 
the  chemical  effect  upon  the  metal,  and  the  evolution  of  electrical  force. 

The  experiments  of  Mr.  Faraday  and  Professor  Daniell  have  given  very 
great  support  to  the  chemical  theory,  by  showing  that  contact  of  dissimilar 
metals  is  not  necessary  in  order  to  call  into  being  powerful  electrical  currents, 
and  that  the  development  of  electrical  force  is  not  only  in 
some  way  connected  with  the  chemical  action  of  the  liquid  of  Fig.  128. 

the  battery,  but  that  it  is  always  in  direct  proportion  to  the 
latter.  One  very  beautiful  experiment,  in  which  decompo- 
sition of  iodide  of  potassium  by  real  electrolysis  is  performed 
by  a  current  generated  without  any  contact  of  dissimilar 
metals,  can  be  thus  made: — A  plate  of  zinc  (fig.  128)  is 
bent  at  a  right  angle,  and  cleaned  by  rubbing  with  sand- 
paper. A  plate  of  platinum  has  a  wire,  of  the  same  metal 
attached  to  it  by  careful  rivetting,  and  the  latter  bent  into 
an  arch.  A  piece  of  folded  filter-paper  is  wetted  with  a  so- 
lution of  iodide  of  potassium,  and  placed  upon  the  zinc ;  the 
platinum  plate  is  arranged  opposite  to  the  latter,  with  the 
end  of  its  wire  resting  upon  the  paper,  and  then  the  pair 
plunged  into  a  glass  of  dilute  sulphui'ic  acid,  mixed  with  a 
few  drops  of  nitric.  A  brown  spot  of  iodine  becomes  in  a  moment  evident 
beneath  the  extremity  of  the  platinum  wire ;  that  is,  at  the  positive  side  of 
the  arrangement. 

A  strong  argument  in  favour  of  the  chemical  view  is  founded  on  the  easily- 
proved  fact,  that  the  direction  of  the  current  is  determined  by  the  kind  of 
action  upon  the  metals,  the  one  least  attacked  being  always  positive.  Let 
two  polished  plates,  the  one  iron  and  the  other  copper,  be  connected  by  wires 
with  a  galvanometer,  and  then  immersed  in  a  solution  of  an  alkaline  sul- 
phide. The  needle  in  a  moment  indicates  a  powerful  current,  passing  from 
the  copper,  through  the  liquid,  to  the  iron,  and  back  again  through  the  wire. 
Let  the  plates  be  now  removed,  cleaned,  and  plunged  into  dilute  acid ;  the 
needle  is  again  driven  round,  but  in  the  opposite  direction,  the  current  now 
passing  from  the  iron,  through  the  liquid,  to  the  copper.  In  .the  first  instance 
the  copper  is  acted  upon,  and  not  the  iron ;  in  the  second,  these  conditions 
are  reversed,  and  with  them  the  direction  of  the  current. 

The  metals  employed  in  the  practical  construction  of  «oltaic  batteries  are 
zinc  for  the  active  metal,  and  copper,  silver,  or,  still  better,  platinum  for  the 
inactive  one  ;  the  greater  the  difference  of  oxidability,  the  better  the  arrange- 
ment. The  liquid  is  either  dilute  sulphuric  acid,  sometimes  mixed  with  a 
little  nitric,  or  occasionally,  where  very  slow  and  long-continued  action  is 
wanted,  salt  and  water.  To  obtain  the  maximum  effect  of  the  apparatus 
with  the  least  expenditure  of  zinc,  that  metal  must  be  employed  in  a  pure 
state,  or  its  surface  must  be  covered  by  or  amalgamated  with  mercury,  which 
in  its  electrical  relations  closely  resembles  the  pure  metal.  The  zinc  is  easily 
brought  into  this  condition  by  wetting  it  with  dilute  sulphuric  acid,  and  then 
rubbing  a  little  mercury  over  it  by  means  of  a  piece  of  rag  tied  to  a  stick 

The  principle  of  the  compound  battery  is,  perhaps,  best  seen  in  the  crown 
of  cups ;  by  each  alternation  of  zinc,  fluid,  and  copper,  the  current  is  urged 
forwai'ds  with  increased  energy,  its  intensity  is  augmented,  but  the  actuai 


192  ELECTRO-CHEMICAL    DECOMPOSITION; 

amount  of  electrical  force  thrown  into  the  current  form  is  not  increased. 
The  quantity,  estimated  by  its  decomposing  power,  is,  in  fact,  determined 
•hy  that  of  the  smallest  and  least  active  pair  of  plates,  the  quantity  of  elec- 
tricity in  every  part  or  section  of  the  circuit  being  exactly  equal.  Hence 
large  and  small  plates,  batteries  strongly  and  weakly  charged,  can  never  be 
connected  without  great  loss  of  power. 

When  a  battery,  either  simple  or  compound,  constructed  with  pure  or  with 
amalgamated  zinc,  is  charged  with  dilute  sulphuric  acid,  a  number  of  highly 
interesting  phenomena  may  be  observed.  While  the  circuit  remains  broken 
the  zinc  is  perfectly  inactive,  no  water  is  decomposed,  no  hydrogen  liberated  ; 
but  the  moment  the  connection  is  completed,  torrents  of  hydrogen  arise, 
not  from  the  zinc,  but  from  the  copper  or  platinum  surfaces  alone,  while  the 
zinc  undergoes  tranquil  and  imperceptible  oxidation  and  solution.  Thus, 
exactly  the  same  effects  are  seen  to  occur  in  every  active  cell  of  a  closed 
circuit,  which  are  witnessed  in  a  portion  of  water  undergoing  electrolysis ; 
the  oxygen  appears  at  the  positive  side,  with  respefct  to  the  current,  and  the 
hydrogen  at  the  negative ;  but  with  this  difference,  that  the  oxygen,  instead 
of  being  set  free,  combines  with  the  zinc.  It  is,  in  fact,  a  real  case  of  elec- 
trolysis, and  electrolytes  alone  are  available  as  exciting  liquids. 

Common  zinc  is  very  readily  attacked  and  dissolved  by  dilute  sulphuric 
acid ;  and  this  is  usually  supposed  .to  arise  from  the  formation  of  a  multitude 
of  little  voltaic  circles,  by  the  aid  of  particles  of  foreign  metals  or  plumbago, 
partially  embedded  in  the  zinc.  This  gives  rise  in  the  battery  to  what  is 
called  local  action,  by  which  in  the  common  forms  of  apparatus  three-fourths 
or  more  of  the  metal  are  often  consumed,  vrithout  contributing  in  the  least 
to  the  general  effect,  but,  on  the  contrary,  injuring  the  latter  to  some  extent. 
This  evil  is  got  rid  of  by  amalgamating  the  surface. 

From  experiments  very  carefully  made  with  a  "dissected"  battery  of 
peculiar  construction,  in  which  local  action  was  completely  avoided,  it  has 
been  distinctly  proved  that  the  quantity  of  electricity  set  in  motion  by  the 
battery  varies  exactly  with  the  zinc  dissolved.  Coupling  this  fact  with  that 
of  the  definite  action  of  the  current,  it  will  be  seen,  that  when  a  perfect 
battery  of  this  kind  is  employed  to  decompose  water,  in  order  to  evolve  1 
grain  of  hydrogen  from  the  latter,  33  grains  of  zinc  must  be  oxidized  and  its 
equivalent  quantity  of  hydrogen  disengaged  in  each  active  cell  of  the  battery. 
That  is  to  say,  that  the  electrical  force  generated  by  the  oxidation  of  an 
equivalent  of  zinc  in  the  battery,  is  capable  of  effecting  the  decomposition 
of  an  equivalent  of  water,  or  any  other  electrolyte  out  of  it. 

This  is  an  exceedingly  important  discovery ;  it  serves  to  show  in  the  most 
striking  manner,  the  intimate  nature  of  the  connection  between  chemical  and 
electrical  forces,  and  their  remarkable  quantitative  or  equivalent  relations. 
It  almost  seems,  to  use  an  expression  of  Mr.  Faraday,  as  if  a  transfer  of 
chemical  force  took  place  through  the  substance  of  solid  metallic  conductors  ; 
that  chemical  actions,  called  into  play  in  one  portion  of  the  circuit,  could  be 
made  at  pleasure  to  exhibit  their  effects  without  loss  or  diminution  in  any 
other.  There  is  an  hypothesis,  not  of  recent  date,  long  countenanced  and 
supported  by  the  illustrious  Berzelius,  which  refers  all  chemical  phenomena 
to  electrical  forces ;  which  supposes  that  bodies  combine  because  they  are  in 
opposite  electrical  states ;  even  the  heat  and  light  accompanying  chemical 
union  may  be,  to  a  certain  extent,  accounted  for  in  this  manner.  In  short, 
we  are  in  such  a  position,  that  either  may  be  assumed  as  cause  or  effect ;  it 
may  be  that  electricity  is  merely  a  form  or  modification  of  ordinary  chemical 
afiinity ;  or,  on  the  other  hand,  that  all  chemical  action  is  a  manifestation 
of  electrical  force. 

One  of  the  most  useful  forms  of  the  common  voltaic  battery  is  that  con- 
U'ived  by  Dr.  Wollaston  (fig.  129).    The  copper  is  made  completely  to  encircle 


OHEMISTEY    OF    THE    VOLTAIC    PILE.  193 

Fig.  129. 


ihe  zinc  jlatc,  except  at  the  edges,  the  two  metals  being  kept  apart  by  pieces 
of  cork  or  wood.  Each  zinc  is  soldered  to  the  preceding  copper,  and  the 
■whole  sciewed  to  a  bar  of  dry  mahogany,  so  that  the  plates  can  be  lifted 
into  or  out  of  the  acid,  which  is  contained  in  an  earthenware  trough,  divided 
into  separate  cells.  The  liquid  consists  of  a  mixture  of  100  parts  water,  2J- 
parts  oil  of  vitriol,  and  2  parts  commercial  nitric  acid,  all  by  measure.  A 
number  of  such  batteries  are  easily  connected  together  by  straps  of  sheet 
copper,  and  admit  of  being  put  into  action  with  great  ease. 

The  great  objection  to  this  and  to  all  the  older  forms  of  the  voltaic  battery 
is,  that  the  power  rapidly  decreases,  so  that  after  a  short  time  scarcely  the 
tenth  part  of  the  original  action  remains.  This  loss  of  power  depends  partly 
on  the  gradual  change  of  the  sulphuric  acid  into  sulphate  of  zinc,  but  still 
more  on  the  coating  of  hydrogen,  and  at  a  later  stage,  on  the  precipitation 
of  metallic  zinc  on  the  copper  plates.  It  is  self-evident 
that  if  the  copper  plate  in  the  fluid  became  covered  Kg.  130. 

with  zinc,  it  would  electrically,  act  like  a  zinc  plate. 
This  is  precisely  the  action  of  the  hydrogen,  whereby 
a  decrease  of  electrical  power  is  produced.  This  effect, 
produced  by  the  substances  separated  from  the  liquid, 
is  commonly  called  polarization. 

An  instrument  of  immense  value  for  the  purposes  of 
electro-chemical  research,  in  which  it  is  desired  to 
maintain  powerful  and  equable  currents  for  many  suc- 
cessive hours,  has  been  contrived  by  Professor  Daniell 
(fig.  130).  Each  cell  of  this  "  constant"  battery  con- 
sists of  a  copper  cylinder  3^  inches  in  diameter,  and 
of  a  height  varying  from  6  to  18  inches.  The  zinc  is 
employed  in  the  form  of  a  rod  f  of  an  inch  in  diameter, 
carefully  amalgamated,  and  suspended  in  the  centre  of 
the  cylinder.  A  second  cell  of  porous  earthenware  or 
animal  membrane  intervenes  between  the  zinc  and  the 
copper ;  this  is  filled  with  a  mixture  of  1  part  by  mea- 
sure of  oil  of  vitriol  and  8  of  water,  and  the  exterior 
space  with  the  same  liquid,  saturated  with  sulphate  of 
copper.  A  sort  of  little  colander  is  fitted  to  the  top  of 
the  cell,  in  which  crystals  of  the  sulphate  of  copper  are  placed,  so  that  tht 


r 


r 


194 


ELECTRO-CHEMICAL    DECOMPOSITION 


Fig.  131. 


strength  of  the  solution  may  remain  unimpaired.  When  a  communication  \^ 
made  by  a  wire  between  the  rod  and  the  cylinder,  a  powerful  current  is  pro- 
duced, the  power  of  which  may  be  increased  to  any  extent,  by  connecting  a 
sufficient  number  of  such  cells  into  a  series,  on  the  principle  of  the  crown 
of  cups,  the  copper  of  the  first  being  attached  to  the  zinc  of  the  second. 
Ten  such  alternations  constitute  a  very  powerful  apparatus,  which  has  the 
great  advantage  of  retaining  its  energy  undiminished  for  a  lengthened  period. 
For  the  copper  plates  become  covered  with  a  compact  precipitate  of  copper 
without  the  evolution  of  any  hydrogen,  so  long  as  the  solution  of  sulphate 
of  copper  remains  saturated.  By  this  most  excellent  arrangement  the  sur- 
faces of  the  copper  plates  retain  their  original  chemical  properties  unchanged. 
The  polarization  is  avoided,  and  the  chief  cause  of  the  gradual  loss  of  powei 
is  removed. 

Mr.  Grove,  on  precisely  the  same  principles,  succeeded  afterwards  in  form 
ing  a  zinc  and  platinum  battery,  the  action  of  which  is  con- 
stant. To  hinder  the  evolution  of  hydrogen  on  the  plati- 
num plates  he  employed  the  oxidizing  action  of  nitric  acid. 
One  of  the  cells  in  this  battery  is  represented  in  the 
margin^  in  section  (fig.  131).  The  zinc  plate  is  bent  round, 
so  as  to  present  a  double  surface,  and  well  amalgamated , 
within  it  stands  a  thin  flat  cell  of  porous  earthenware,  filled 
with  strong  nitric  acid,  and  the  whole  is  immersed  in  a 
mixture  of  1  part  by  measure  of  oil  of  vitriol  and  6  of 
water,  contained  either  in  one  of  the  cells  of  Wollaston's 
trough,  or  in  a  separate  cell  of  glazed  porcelain,  made  for 
the  purpose.  The  apparatus  is  completed  by  a  plate  of 
platinum  foil  which  dips  into  the  nitric  acid,  and  forms  the 
positive  side  of  the  arrangement.  With  ten  such  pairs, 
experiments  of  decomposition,  ignition  of  wires,  the  light 
between  charcoal  points,  &c.,  can  be  exhibited  with  great 
brilliancy,  while  the  battery  itself  is  very  compact  and 
j>ortable,  and,  to  a  great  extent,  constant  in  its  action.  The  zinc,  as  in  the 
case  of  Professor  Daniell's  battery,  is  only  consumed  while  the  current 
passes,  so  that  the  apparatus  may  be  arranged  an  hour  or  two  before  it  is 
required  for  use,  which  is  often  a  matter  of  great  convenience.  The  nitrio 
acid  suppresses  the  whole  of  the  hydrogen,  becoming  thereby  slowly  deoxi- 
dized and  converted  into  nitrous  acid,  which  at  first  remains  dissolved,  but 
after  some  time  begins  to  be  disengaged  from  the  porous  cells  in  dense  red 
fames ;  this  constitutes  the  only  serious  drawback  to  this  excellent  instru- 
ment. 

Professor  Bunsen  has  modified  the  Grove  battery  by  substituting  for  the 
platinum,  dense  charcoal  or  coke,  which  is  an  excellent  conductor  of  elec- 
tricity. By  this  alteration,  at  a  very  small  expense,  a  battery  may  be  made 
as  powerful  and  useful  as  that  of  Grove.  On  account  of  its  cheapness,  an^ 
one  may  put  together  one  hundred  or  more  of  Bunsen's  cells ;  by  which  the 
most  magnificent  phenomena  of  heat  and  light  may  be  obtained. 

Mr.  Smee  has  contrived  an  ingenious  battery,  in  which  silver  covered  with 
thin  coating  of  finely-divided  metallic  platinum  is  employed  in  association 
with  amalgamated  zinc  and  dilute  sulphuric  acid.    The  rough  surface  appears 
to  permit  the  ready  disengagement  of  the  bubbles  of  hydrogen. 

Within  the  last  nine  or  ten  years,  several  very  beautiful  and  successful 
applications  of  voltaic  electricity  have  been  made,  which  may  be  slightlj* 
mentioned.  Mr.  Spencer  and  Professor  Jacobi  have  employed  it  in  copying, 
or  rather  in  multiplying,  engraved  plates  and  medals,  by  depositing  upon 
their  surfaces  a  thin  coating  of  metallic  copper,  which,  when  separated  from 
the  original,  exhibits,  in  reverse,  a  most  faithful  representation  of  the  latter. 


CHEMISTRY    OF    THE    VOLTAIC    PILE. 


195 


Fig.  132. 


By  using  this  in  its  turn  as  a  mould  or  matrix,  an  absolutely  perfect  fac- 
simile  of  the  plate  or  medal  is  tbtained.  In  the  former  case, 
the  impressions  taken  on  paper  are  quite  indistinguishable  from 
those  directly  derived  from  the  work  of  the  artist ;  and  as  there 
is  no  limit  to  the  number  of  electrotype  plates  which  can  be  thus 
produced,  engravings  of  the  most  beautiful  description  may  be 
multipliied  indefinitely.  The  copper  is  very  tough,  and  bears 
the  action  of  the  press  perfectly  well. 

The  apparatus  used  in  this  and  many  similar  processes  is 
of  the  simplest  possible  kind.  A  trough  or  cell  of  wood  (fig. 
132)  is  divided  by  a  porous  diaphragm,  made  of  a  very  thin 
piece  of  sycamore,  into  two  parts ;  dilute  sulphuric  acid  is  put 
on  one  side,  and  a  saturated  solution  of  sulphate  of  copper, 
sometimes  mixed  with  a  little  acid,  on  the  other.  A  plate  of 
zinc  is  soldered  to  a  wire  or  strap  of  copper,  the  other  end  of 
which  is  secured  by  similar  means  to  the  engraved  copper 
plate.  The  latter  is  then  immersed  in  the  solution  of  sulphate, 
and  the  zinc  in  the  acid.  To  prevent  deposition  of  copper  on  the  back  of 
the  copper  plate,  that  portion  is  covered  with  varnish.  For  medals  and 
small  works  a  porous  earthenware  cell,  placed  in  a  jelly -jar,  may  be  used. 

Other  metals  may  be  precipitated  in  the  same  manner,  in  a  smooth  and 
compact  form,  by  the  use  of  certain  precautions  which  have  been  gathered 
by  experience.  Electro-gilding  and  plating  are  now  carried  on  very  largely 
and  in  great  perfection  by  Messrs.  Elkington  and  others.  Even  non-conduct- 
ing bodies,  as  sealing-wax  and  plaster  of  Paris,  may  be  coated  with  metal ; 
it  is  only  necessary,  as  Mr.  Murray  has  shown,  to  rub  over  them  the  thin- 
nest possible  film  of  plumbago.  Seals  may  thus  be  copied  in  a  very  few 
hours  with  unerring  truth. 

M.  Becquerel,  several  years  ago,  published  an  exceedingly  interesting  ac- 
count of  certain  experiments,  in  which  crystallized  metals,  oxides,  and  other 
insoluble  substances  had  been  produced  by  the  slow  and  continuous  action 
of  feeble  electrical  currents,  kept  up  for  months,  or  even  years.  These  pro- 
ducts exactly  resembled  natural  minerals,  and,  indeed,  the  experiments 
threw  great  light  on  the  formation  of  the  latter  within  the  earth.' 

The  common  but  very  pleasing  experiment  of  the  lead  tree  is  greatly  de- 
pendent on  electro-chemical  action.  When  a  piece  of  zinc  is 
suspended  in  a  solution  of  acetate  of  lead,  the  first  efi^ect  is 
the  decomposition  of  a  portion  of  the  latter,  and  the  deposi- 
tion of  metallic  lead  upon  the  surface  of  the  zinc ;  it  is  simply 
a  displacement  of  a  metal  by  a  more  oxidable  one.  The 
change  does  not,  however,  stop  here ;  metallic  lead  is  still 
deposited  in  large  and  beautiful  plates  upon  that  first  thrown 
down,  until  the  solution  becomes  exhausted,  or  the  zinc  en- 
tirely disappears.  (Fig.  133.)  The  first  portions  of  lead  form 
with  the  zinc  a  voltaic  arrangement  of  sufficient  power  to  de- 
compose the  salt,  under  the  peculiar  circumstances  in  which 
the  latter  is  placed,  the  metal  is  precipitated  upon  the  nega- 
tive portion,  that  is,  the  lead,  while  the  oxygen  and  acid  are 
taken  up  by  the  zinc. 

Professor  Grove  has  contrived  a  battery,  in  which  an  elec- 
trical current,  of  sufficient  intensity  to  decompose  water,  is  produced  by  the 
reaction  of  oxygen  upon  hydrogen.     Each  element  of  this  interesting  appa- 
ratus consists  of  a  pair  of  glass  tubes  to  contain  the  gases,  dipping  into  a 
vessel  of  acidulated  water.      Both  tubes  contain  platinum  plates,  covered 


Fig.  133 


*  Traits  de  I'Electridtfi  et  du  Magn6tisme,  iii.  239. 


196         ELECTRO-CHEMICAL    DECOMPOSITION. 

with  a  rough  deposit  of  finely-divided  platinum,  and  furnished  with  conducting 
wires,  which  pass  through  the  tops  or  sides  of  the  tubes,  and  are  hermeti- 
cally sealed  into  the  latter.  When  the  tubes  are  charged  with  oxygen  on  the 
one  side  and  hydrogen  on  the  other,  and  the  wires  connected  with  a  galvano- 
scope,  the  needle  of  the  instrument  becomes  instantly  affected ;  and  when 
ten  or  more  are  combined  in  a  series,  the  oxygen-tube  of  the  one  with  the 
hydrogen- tube  of  the  next,  &o.,  while  the  terminal  wires  dip  into  acidulated 
water,  a  rapid  stream  of  minute  bubbles  from  either  wire  indicates  the  de- 
composition of  the  liquid ;  and  when  the  experiment  is  made  with  a  small 
voltameter,  it  is  found  that  the  oxygen  and  hydrogen  disengaged,  exactly 
equal  in  amount  the  quantities  absorbed  by  the  act  of  combination  in  <««ch 
tube  of  the  battery. 


CHEMISTRY     OF    THE    METALS.  197 


CHEMISTRY  OF  THE  METALS. 


Tj'w  >fiji&.l3  constitute  the  second  and  larger  group  of  elementary  bodies 
i  gveaf  fluniLer  of  these  are  of  very  rare  occurrence,  being  found  only  in  a 
ft  »;r  sca\  ce  mirerals ;  others  are  more  abundant,  and  some  few  almost  uni- 
versally diffused  throughout  the  whole  globe.  Some  of  these  bodies  are  of 
most  importance  when  in  the  metallic  state ;  others,  when  in  combination, 
chiefly  as  oxides,  the  metals  themselves  being  almost  unknown.  Many  are 
used  in  medicine  and  in  the  arts,  and  are  essentially  connected  with  the  pro- 
gi'ess  of  civilization. 

If  arsenic  and  tellurium  bo  included,  the  metals  amount  to  forty-nine  ia 
number. 

Physical  Properties.  —  One  of  the  most  remarkable  and  striking  characters 
possessed  by  the  metals  is  their  peculiar  lustre ;  this  is  so  characteristic,  that 
the  expression  metallic  lustre  has  passed  into  common  speech.  This  pro- 
perty is  no  doubt  connected  with  the  extraordinary  degree  of  opacity  which 
the  metals  present  in  every  instance.  The  thinnest  leaves  or  plates,  the  edges 
of  crystalline  laminse,  arrest  the  passage  of  light  in  the  most  complete  man- 
ner. An  exception  to  this  rule  is  usually  made  in  favour  of  gold-leaf,  which 
when  held  up  to  the  daylight  exhibits  a  greenish  colour,  as  if  it  were  really 
endued  with  a  certain  degree  of  translucency  ;  the  metallic  film  is,  however, 
always  so  imperfect,  that  it  becomes  difficult  to  say  whether  the  observed 
effect  may  not  be  in  some  measure  due  to  multitudes  of  little  holes,  many  of 
which  are  visible  to  the  naked  eye. 

In  point  of  colour,  the  metals  present  acertain  degree  of  uniformity;  with 
two  exceptions,  viz.  copper,  which  is  red,  and  gold,  which  is  yellow,  all  these 
bodies  are  included  between-  the  pure  white  of  silver,  and  the  bluish-grey 
tint  of  lead ;  bismuth,  it  is  true,  has  a  pinkish  colour,  but  it  is  very  feeble. 

The  differences  of  specific  gravity  are  very  wide,  passing  from  potassium 
and  sodium,  which  are  lighter  than  water,  to  platinum,  which  is  nearly 
twenty-one  times  heavier  than  an  equal  bulk  of  that  fluid. 

Table  of  the  Specific  Gravities  of  Metals  at  60°  (15o-5C).' 

Platinum  20-98 

Gold  19-26 

Tungsten 17-60 

Mercury 13-57 

Palladium 11-30  to  11-8 

Lead  11-35 

Silver 10-47 

Bismuth 9-82 

Uranium 1 900 

Copper .' 8-89 

Cadmium  8-60 

»Dr.  Turner's  Elements,  eighth  edition,  p. 345. 
17» 


198  CHEMISTRY    OP    THE    METALS. 

Cobalt 8-54 

Nickel 8-28 

Iron 3-79 

Molybdenum 7-40 

Tin 7-29 

Zinc 7-86  to  7-1 

Manganese 6-85 

Antimony 6-70 

Tellurium 611 

Arsenic 5-88 

Aluminium 2-60* 

Magnesium 1-70 

Sodium 0-972 

Potassium 0-865 

The  property  of  malleability,  or  power  of  extension  under  the  hammer 
or  between  the  rollers  of  the  flatting-mill,  is  enjoyed  by  certain  of  the 
metals  to  a  very  great  extent.  Gold-leaf  is  a  remarkable  example  of  the 
tenuity  to  which  a  malleable  metal  may  be  brought  by  suitable  means.  The 
gilding  on  silver  wire  used  in  the  manufacture  of  gold  lace  is  even  thinner, 
and  yet  presents  an  unbroken  surface.  Silver  may  be  beaten  out  very  thin  ; 
copper  also,  but  to  an  inferior  extent ;  tin  and  platinum  are  easily  rolled  out 
into  foil ;  iron,  palladium,  lead,  nickel,  cadmium,  the  metals  of  the  alkalis, 
and  mercury,  when  solidified,  are  also  malleable.  Zinc  may  be  placed  mid- 
way between  the  malleable  and  brittle  division ;  then  perhaps  bismuth,  and, 
lastly,  such  metals  as  antimony  and  arsenic,  which  are  altogether  destitute 
of  malleability. 

The  specific  gravity  of  malleable  metals  is  usually  very  sensibly  increased 
by  pressure  or  blows,  and  the  metals  themselves  rendered  much  harder,  with 
a  tendency  to  brittleness.  This  condition  is  destroyed  and  the  former  soft 
state  restored  by  the  operation  of  annealing,  which  consists  in  heating  the 
metal  to  redness  out  of  contact  with  air  (if  it  will  bear  that  temperature 
without  fusion)  and  cooling  it  quickly  or  slowly  according  to  the  circum- 
stances of  the  case.  After  this  operation  it  is  foimd  to  possess  its  original 
specific  gravity. 

Ductility  is  a  property  distinct  from  the  last,  inasmuch 
Fig.  134.  as  it  involves  the  principle  of  tenacity,  or  power  of  re- 

sisting tension.  The  art  of  wire-drawing  is  one  of  great 
/^\  r\  antiquity ;  it  consists  in  drawing  rods  of  metal  through  a 
•  *  '  •  ■  succession  of  trumpet-shaped  holes  in  a  steel  plate  (fig. 
134),  each  being  a  little  smaller  than  its  predecessor,  until 
the  requisite  degree  of  fineness  is  attained.  The  metal 
often  becomes  very  hard  and  rigid  in  this  process,  and  is 
then  liable  to  break ;  this  is  remedied  by  annealing.     The 

Wi      w         order  of  tenacity  among  the  metals  susceptible  of  being 
Vl/         easily  drawn  into  wire  is  the  following :  it  is  determined 
by  observing  the  weights  required  to  break  asunder  wires 
Irawn  through  tne  same  orifice  of  the  plate : 


Iron 

Gold 

Copper 

Zinc 

Platinum 

Tin 

Silver 

Lead 

Metals  differ  as  much  In  fusibility  as  in  density ;  the  following  table,  ex- 
»  WaWsr. 


CHEMISTRY     OP    THE     METALS. 


199 


Fusible  below 
a  red  heat 


tracted  from  the  late  Dr.  Turner's  excellent  work,  will  give  an  idea  of  their 
relations  to  heat.  The  melting-points  of  the  metals  which  only  fuse  at  a 
temperature  above  ignition,  and  that  of  zinc,  are  on  the  authority  of  Mr. 
Daniell,  having  been  observed  by  the  help  of  the  pyrometer  before  described ; 

Melting  points. 
F.  C. 

Mercury — 39°  — 39°-44 

Potassium 136  57-77 

Sodium  194  90 

Tin 442  227-77 

Cadmium (about)  442  277-77 

Bismuth 497  258-33 

Lead 612  322-77 

Tellurium — rather  less  fusible  than  lead 
Arsenic — unknown 

Zinc 773  411-66 

^Antimony— just  below  redness 

fSilver 1873     1022-77 

Copper  1996     1091-11 

Gold  ;. : 2016     1102-22 

Cast  iron 2786     1530 

Pure  iron ' 

Nickel 

Cobalt 

Manganese.... 
Palladium  .... 
Molybdenum . 

Tungsten ^     Imperfectly  melted  in  wind-fumace. 

Chromium... 


Infusible  below  < 
a  red  heat 


Fusible  only  in  an  excellent  wind- 
furnace. 


Titanium  . 
Cerium.... 
Osmium... 
Iridium  ... 
Rhodium  . 
Platinum . 
Tantalum 


Infusible  in  furnace ;  fusible  by  oxy- 
hydrogen  blowpipe. 


Some  metals  acquire  a  pasty  or  adhesive  state  before  becoming  fluid  ;  this 
is  the  case  with  iron  and  platinum,  and  also  with  the  metals  of  the  alkalis. 
It  is  this  peculiarity  which  confers  the  very  valuable  property  of  welding, 
by  which  pieces  of  iron  and  steel  are  united  without  solder,  and  the  finely- 
divided  metallic  sponge  of  platinum  converted  into  a  solid  and  compact  bar. 

Volatility  is  possessed  by  certain  members  of  this  class,  and  perhaps  by 
all,  could  temperatures  sufficiently  elevated  be  obtained.  Mercury  boils  and 
distils  below  a  red  heat;  potassium,  sodium,  zinc,  and  cadmium,  rise  in 
vapour  when  heated  to  a  bright  redness ;  arsenic  and  tellurium  are  volatile. 

CHEMICAL   EELATIONS    OF   THE   METALS  ;    CONSTITUTION    OF   SALTS. 

Metallic  combinations  are  of  two  kinds ;  namely,  those  formed  by  the 
union  of  metals  among  themselves,  which  are  called  alloys,  or  where  mer- 
cury is  concerned,  amalgams,  and  those  generated  by  combination  with  the 
non-metallic  elements,  as  oxides,  chlorides,  sulphides,  &c.  In  this  latter 
case  the  metallic  characters  are  very  frequently  lost.  The  alloys  themselves 
are  really  true  chemical  compounds,  and  not  mere  mixtures  of  the  consti- 


Oxygen. 

Symbols. 

Characters. 

leq.     . 
3  eq.     . 
2  eq.     . 

..     MnO     ... 
..     MdoO.  ... 
..     MnOa   ... 

Strongly  basic. 
Feebly  basic. 
Neutral. 

3  eq.     . 
7eq.     ., 

Strongly  acid. 

200  CHEMISTRY    OP     THE     METALS. 

tuent  metals ;  their  properties  often  differ  completely  from  those  of  the 
latter. 

The  oxides  of  the  metals  may  be  divided,  as  already  pointed  out,  into 
three  classes ;  namely,  those  which  possess  basic  characters  more  or  less 
marked,  those  which  refuse  to  combine  with  either  acids  or  alkalis,  and  those 
which  have  distinct  acid  properties.  The  strong  bases  are  all  protoxides ; 
they  contain  single  equivalents  of  metal  and  oxygen ;  the  weaker  bases  are 
usually  sesquioxides,  containing  metal  and  oxygen  in  the  proportion  of  two 
equivalents  of  the  former  to  three  of  the  latter ;  the  peroxides  or  neutral 
compounds  are  still  richer  in  oxygen,  and,  lastly,  the  metallic  acids  contain 
the  maximum  proportion  of  that  element. 

The  gradual  change  of  properties  by  increasing  proportions  of  oxygen  is 
well  illustrated  by  the  case  of  manganese. 

Metal. 

Protoxide 1  eq. 

Sesquioxide 2  eq. 

Binoxide 1  eq. 

Manganic  acid 1  eq. 

Permanganic  acid 2  eq. 

The  oxides  of  iron  and  chromium  present  similar,  but  less  numerous  gra- 
dations. 

When  a  powerful  oxygen-acid  and  a  powerful  metallic  base  are  united  in 
such  proportions  that  they  exactly  destroy  each  other's  properties,  the  re- 
sulting salt  is  said  to  be  neutral ;  it  is  incapable  of  affecting  vegetable 
colours.  Now,  in  all  these  well-characterized  neutral  salts,  a  constant  and 
very  remarkable  relation  is  observed  to  exist  between  the  quantity  of  oxygen 
in  the  base,  and  the  quantity  of  acid  in  the  salt.  This  relation  is  expressed 
in  the  following  manner :  —  To  form  a  neuti'al  combination,  as  many  equiva- 
lents of  acid  must  be  present  in  the  salt  as  there  are  of  oxygen  in  the  base 
itself.  In  fact,  this  has  become  the  very  definition  of  neutrality,  as  the 
action  on  vegetable  colours  is  sometimes  an  unsafe  guide. 

It  is  easy  to  see  the  application  of  this  law.  When  a  base  is  a  protoxide, 
a  single  equivalent  of  acid  suffices  to  neutralize  it ;  when  a  sesquioxide,  not 
less  than  three  are  required.  Hence,  if  by  any  chance,  the  base  of  a  salt 
should  pass  by  oxidation  from  the  one  state  to  the  other,  the  acid  will  be  in- 
sufficient in  quantity  by  one-half  to  form  a  neutral  combination.  Sulphate 
of  the  protoxide  of  iron  offers  an  example ;  when  a  solution  of  this  substance 
is  exposed  to  the  air,  it  absorbs  oxygen,  and  a  yellow  insoluble  sub-salt,  or 
b-isic-salt,  is  produced,  which  contains  an  excess  of  base.  Four  equivalents 
of  the  green  compound  absorb  from  the  air  two  equivalents  of  oxygen,  and 
give  rise  to  one  equivalent  of  neutral  and  one  equivalent  of  basic  sulphate 
of  the  sesquioxide,  as  indicated  by  the  diagonal  zigzag  line  of  division. 

1  eq.  iron  -j-  1  eq.  oxygen 1  eq.  sulphuric  acid. 

1  eq.  iron  -|-  1  eq.  oxygen 1  eq.  sulphuric  acid. 

i    ~\-  1  eq.  oxygen  from  air 

1  eq.  iron  -|-  1  eg.  oxygen 1 1  eq.  sulphuric  acid. 

1  eq,  iron  -\-  1  eq.  oxygen 1  eq.  sulphuric  acid. 

-|-  1  eq.  oxygen  from  air. 

Such  sub-salts  or  basic  salts  are  very  frequently  insoiuble. 

The  combinations  of  chlorine,  iodine,  bromine,  and  fluorine  with  the  uietals 
possess  in  a  very  high  degree  the  saline  character.  If,  however,  the  definition 
formerly  given  of  a  salt  be  rigidly  adhered  to,  these  bodies  must  be  excluded 
from  the  class,  and  with  them  the  very  substance  from  which  the  name  is 


CHEMISTRY    OF    THE    METALS.  £01 

derived,  that  is,  common  salt,  which  is  a  chloride  of  sodium  To  obviate 
this  anomaly,  it  has  been  found  necessary  to  create  two  classes  of  salts ;  in 
the  first  division  will  stand  those  constituted  after  the  type  of  common  salt, 
which  contain  a  metal  and  a  salt-radical,  as  chlorine,  io^e,  &c. ;  and  in  the 
second,  those  which,  like  sulphate  of  soda  and  nitrate  of  potassa,  are  gene- 
rally supposed  to  be  combinations  of  an  acid  with  an  oxide.  The  names 
haloid '^  salts,  and  ozy gen-acid,  or  ozy-salts,  are  given  to  these  two  kinds. 

When  a  haloid  salt  is  dissolved  in  water,  it  might  be  regarded  as  a  combi- 
nation of  a  metallic  oxide  with  a  hydrogen-acid,  the  water  being  supposed 
to  undergo  decomposition,  its  hydrogen  being  transferred  to  the  salt-radical, 
and  its  oxygen  to  the  metal.  This  view  is  unsupported  by  evidence  of  any 
value :  it  is  much  more  probable,  indeed,  that  no  truly  saline  compounds  of 
hydrogen-acids  exist,  at  any  rate  in  inorganic  chemistry.  When  a  solution 
of  any  hydrogen-acid  is  poured  upon  a  metallic  oxide,  we  may  rather  suppose 
that  both  are  decomposed,  water  and  a  haloid  salt  of  the  metal  being  pro- 
duced.    Take  hydrochloric  acid  and  potassa  by  way  of  example. 

Hydrochloric   f  Chlorine  — — -^^  Chloride  of  potassium. 

acid \  Hydrogen -^,^ 

Potassa lo™"^__:r-^„. 

I  Oxygen ^=s>^^yater. 

On  evaporating  the  solution,  the  chloride  of  potassium  crystallizes  out. 

When  hydrochloric  acid  and  ammoniacal  gases  are  mixed,  they  combine 
with  some  energy  and  form  a  white  solid  salt,  sal-ammoniac.  Now  this  sub- 
stance bears  such  a  strong  resemblance  in  many  important  particulars  to 
chloride  of  potassium  and  common  salt,  that  the  ascription  to  it  of  a  similar 
constitution  is  well  warranted. 

If  chloride  of  potassium,  therefore,  contain  chlorine  and  metal,  sal-ammo- 
niac may  also  contain  chlorine  in  combination  with  a  substance  having  the 
chemical  relations  of  a  metal,  formed  by  the  addition  of  the  hydrogen  of  the 
acid  to  the  elements  of  the  ammonia. 

Hydrochloric  f  1  eq.  Chlorine Chlorine  ...  ^ 

acid (1  eq.  Hydrogen  '"         gal- 

Ammonia  ...  /  ?  ^^-  S.y.'^'^^^''^^^^^::::^^  1  ammoniac. 

\  1  eq.  Nitrogen ^^^^^^^^  Ammonium  J 

The  term  ammonium  is  given  to  this  hypothetical  body,  NH^ ;  it  is  sup- 
posed to  exist  in  all  the  ammoniacal  salts.  Thus  we  have  chloride  of 
ammonium,  sulphate  of  the  oxide  of  ammonium,  &c.  This  view  is  very 
strongly  supported  by  the  peculiarities  of  the  salts  themselves,  and  by  the 
existence  of  a  series  of  substances  intimately  related  to  these  salts  in  organic 
chemistry,  as  will  hereafter  be  seen. 

Many  of  the  sulphides  also  possess  the  saline  character  and  are  soluble  in 
water,  as  those  of  potassium  and  sodium.  Sometimes  a  pair  of  sulphides 
will  unite  in  definite  proportions,  and  form  a  crystallizable  compound.  Such 
bodies  bear  a  very  close  resemblance  to  oxygen-acid  salts ;  they  usually 
contain  a  protosulphide  of  an  alkaline  metal,  and  a  higher  sulphide  of  a  non- 
metallic  substance  or  of  a  metal  which  has  little  tendency  to  form  a  basic 
oxide,  the  two  sulphides  having  exactly  the  same  relation  to  each  other  as 
the  oxide  and  acid  of  an  ordinary  salt.  Hence  the  expressions  sulphur-salt, 
sulphur-add,  and  sulphur-base,  which  Berzelius  applies  to  such  compounds ; 
they  contain  sulphur  in  the  place  of  oxygen.  Thus,  bisulphide  of  carbon  is 
a  sulphur-acid ;  it  forms  a  crj^tallizable  compound  with  protosulphide  of 
potassium,  which  is  a  sulphur-base.  Were  oxygen  substituted  for  the  sulphur 
in  this  product,  we  should  have  carbonate  of  potassa. 

*  £A(,  sea-salt,  and  Hhoi,  form. 


2vy2  CHEMISTRY    OP    THE    METALS. 

KS + CSj  sulphur-salt.  "'•'■' 

KO-f-COj  oxygen-salt. 

These  remarkable  compounds  are  very  numerous  and  interesting ;  they 
have  been  studied  by  Berzelius  with  great  care. 

Salts  often  combine  together,  and  form  -what  are  called  double  salts,  in 
which  the  same  acid  is  in  combination  with  two  different  bases.  When  sul- 
phate of  copper  and  sulphate  of  potassa,  or  chloride  of  zinc  and  sal-ammoniac, 
are  mixed  in  the  ratio  of  the  equivalents,  dissolved  in  water,  and  the  solution 
made  to  crystallize,  double  salts  are  obtained.  These  latter  are  often  more 
beautiful,  and  crystallize  better  than  their  constituent  salts. 

Many  of  the  compounds  called  super,  or  acid  salts,  such  as  bisulphate  of 
potassa,  which  have  a  sour  taste  and  acid  reaction  to  test-paper,  ought 
strictly  to  be  considered  in  the  light  of  double  salts,  in  which  one  of  the 
bases  is  water.  Strange  as  it  may  at  first  sight  appear,  water  possesses 
considerable  basic  powers,  although  it  is  unable  to  mask  acid  reaction  on 
vegetable  colours ;  hydrogen,  in  fact,  very  much  resembles  a  metal  in  its 
chemical  relations.  Bisulphate  of  potassa  will,  therefore,  be  a  double  sul- 
phate of  potassa  and  water,  while  oil  of  vitriol  must  be  assimilated  to  neutral 
Bulphate  of  potassa. 

KO+SO,  and  HO-f  SO,. 

Water  is  a  weak  base ;  it  is  for  the  most  part  easily  displaced  by  a  metallic 
oxide ;  yet  cases  occur  now  and  then  in  which  the  reverse  happens,  and 
water  is  seen  to  decompose  a  salt,  in  virtue  of  its  basic  power. 

There  are  few  acid  salts  which  contain  no  water ;  as  the  bichromate  of 
potassa,  and  a  new  anhydrous  sulphate  of  potassa  discovered  by  M.  Jaque- 
lain.»  It  will  be  necessary,  of  course,  to  adopt  some  other  view  in  these 
cases.  The  simplest  will  be  to  consider  them  as  really  containing  two  equi- 
valents of  acid  to  one  of  base. 

By  water  of  crystallization  is  meant  water  in  a  somewhat  loose  state  of  com- 
bination with  a  salt,  or  other  compound  body,  from  which  it  can  be  disen- 
gaged by  the  mere  application  of  heat,  or  by  exposure  to  a  dry  atmosphere. 
Salts  which  contain  water  of  crystallization  have  their  crystalline  form  greatly 
influenced  by  the  proportion  of  the  latter.  Green  sulphate  of  iron  crystal- 
lizes in  two  diflFerent  forms,  and  with  two  different  proportions  of  water, 
according  to  the  temperature  at  which  the  salt  separates  from  the  solution. 

Many  salts  containing  water  effloresce  in  a  dry  atmosphere,  crumbling  to 
powder,  and  losing  part  or  the  whole  of  their  water  of  crystallization ;  while 
in  a  moist  atmosphere  they  may  be  preserved  unchanged.  The  opposite 
effect  to  this,  or  deliquescence,  results  from  a  strong  attraction  of  the  salt  for 
water,  in  virtue  of  which  it  absorbs  the  latter  from  the  air,  often  to  the 
extent  of  liquefaction. 

Crystallization;  Crystalline  Forms. — Almost  every  substance,  simple  and 
compound,  capable  of  existence  in  the  solid  state,  assumes,  under  fav(?urable 
circumstances,  a  distinct  geometrical  form  or  figure,  usually  bounded  by 
plane  surfaces,  and  having  angles  of  fixed  and  constant  value.  The  faculty 
of  crystallization  seems  to  be  denied  only  to  a  few  bodies,  chiefly  highly 
complex  organic  principles,  which  stand,  as  it  were,  upon  the  very  edge  of 
organization,  and  which,  when  in  a  solid  state,  are  frequently  characterized 
by  a  kind  of  beady  or  globular  appearance,  well  known  to  microscopical 
observers. 

The  most  beautiful  examples  of  crystallization  are  to  be  found  among 
natural  minerals,  the  result  of  exceedingly  slow  changes  constantly  occurring 
within  the  earth ;  it  is  invariably  found  that  artificial  crystals  of  salts,  and 

»  Ann.  Chim.  et  Phys.  Ixx.  311. 


CHEMISTRY    OP    THE    METALS. 


203 


other  soluble   substances,  "w^liich  have  been   slowly  and  quietly  deposited, 
always  surpass  in  size  and  regularity  those  of  more  rapid  formation. 

Solution  in  water  or  some  other  liquid  is  one  very  frequent  method  of 
effecting  crystallization.  If  the  substance  be  more  soluble  at  a  high  than  at 
a  lower  temperature,  then  a  hot  and  saturated  solution  by  slow  cooling  will 
generally  be  found  to  furnish  crystals ;  this  is  a  very  common  case  with  salts 
and  various  organic  principles.  If  it  be  equally  soluble,  or  nearly  so,  at  all 
temperatures,  then  slow  spontaneous  evaporation  in  the  air,  or  over  a  sur- 
face of  oil  of  vitriol,  often  proves  very  effective. 

Fusion  and  slow  cooling  may  be  employed  in  many  cases ;  that  of  sulphur 
s  a  good  example ;  the  metals  usually  afford  traces  of  crystalline  figure 
when  thus  treated,  which  sometimes  become  very  beautif\il  and  distinct,  as 
with  bismuth.  A  third  condition  under  which  crystals  very  often  form  is  in 
passing  from  a  gaseous  to  a  solid  state,  of  which  iodine  affords  a  good  in- 
stance. When  by  any  of  these  means  time  is  allowed  for  the  symmetrical 
arrangement  of  the  particles  of  matter  at  the  moment  of  solidification, 
crystals  are  produced. 

That  crystals  owe  their  figure  to  a  certain  regularity  of  internal  structure, 
is  shown  both  by  their  mode  of  formation  and  also  by  the  peculiarities  at- 
tending their  fracture.  A  crystal  placed  in  a  slowly-evaporating  saturated 
solution  of  the  same  substance  grows  or  increases  by  a  continued  deposition 
of  fresh  matter  upon  its  sides  in  such  a  manner  that  the  angles  formed  by 
the  meeting  of  the  latter  remain  unaltered. 

The  tendency  of  most  crystals  to  split  in  particular  directions,  called  by 
mineralogists  cleavage,  is  a  certain  indication  of  regular  structure,  while  the 
curious  optical  properties  of  many  among  them,  and  their  remarkable  mode 
of  expansion  by  heat,  point  to  the  same  conclusion. 

It  may  be  laid  down  as  a  general  rule  that  every  substance  has  its  own 
crystalline  form,  by  which  it  may  very  frequently  be  recognized  at  once ; 
not  that  each  substance  has  a  different  figure,  although  very  great  diversity 
in  this  respect  is  to  be  found.  Some  forms  are  much  more  common  than 
others,  as  the  cube  and  six-sided  prism,  which  are  very  frequently  assumed 
by  a  number  of  bodies,  not  in  any  way  related. 

The  same  substance  may  have,  under  different  sets  of  circumstances,  as 
high  and  low  temperatures,  two  different  crystalline  forms,  in  which  case  it 
is  said  to  be  dimorphous.  Sulphur  and  carbon  furnish,  as  already  noticed, 
examples  of  this  curious  fact ;  another  case  is  presented  by  carbonate  of 
lime  in  the  two  modifications  of  calcareous  spar  and  arragonite,  both  chemi- 
cally the  same,  but  physically  different.  A  fourth  example  might  be  given 
in  the  iodide  of  mercury,  which  also  has  two  distinct  forms,  and  even  two 
distinct  colours,  offering  as  great  a  contrast  as  those  of  diamond  and  plum- 
bago. 

Fig.  135. 


204 


CHEMISTRY    OP    THE    METALS. 


The  angles  of  crystals  are  measured  by  means  of  instruments  called  goni- 
ometers, of  which  tiiere  are  two  kinds  in  use,  namely,  the  old  or  common 
goniometer,  and  the  reflective  goniometer  of  Dr.  Wollaston. 

The  common  goniometer  consists  of  a  pair  of  steel  blades  moving  with 
friction  upon  a  centre,  as  shown  in  the  cut  (fig.  135).  The  edges  a  a  are 
carefully  adjusted  to  the  faces  of  the  crystal,  whose  inclination  to  each  other 
it  is  required  to  ascertain,  and  then  the  instrument  being  applied  to  the  di- 
vided semicircle,  the  contained  angle  is  at  once  read  off.  An  approximative 
measurement,  within  one  or  two  degrees,  can  be  easily  obtained  by  this  in- 
strument, provided  the  planes  of  the  crystal  be  tolerably  perfect,  and  large 
enough  for  the  purpose.  Some  practice  is  of  course  required  before  even 
this  amount  of  accuracy  can  be  attained. 

The  reflective  goniometer  is  a  very  superior  instrument,  its  indications  be- 
ing correct  within  a  fraction  of  a  degree ;  it  is  applicable  also  to  the  mea- 
Burement  of  the  angles  of  crystals  of  very  small  size,  the  only  condition 
required  being  that  their  planes  be  smooth  and  brilliant.  The  subjoined 
sketch  (fig.  136)  will  convey  an  idea  of  its  nature  and  mode  of  use. 

Pig.  136. 


a  is  a  divided  circle  or  disc  of  brass,  the  axis  of  which  passes  stiffly  and 
without  shake  through  the  support  h.  This  axis  is  itself  pierced  to  admit 
the  passage  of  a  round  rod  or  wire,  terminated  by  the  milled-edged  head  c, 
and  destined  to  carry  the  crystal  to  be  measured  by  means  of  the  jointed 
arm  d.  A  vernier,  e,  immovably  fixed  to  the  upright  support,  serves  to  mea- 
sure with  great  accuracy  the  angular  motion  of  the  divided  circle.  The 
crystal  at  /  can  thus  be  turned  round,  or  adjusted  in  any  desired  position, 
without  the  necessity  of  moving  the  disc. 

The  principle  upon  which  the  measurement  of  the  angle  rests  is  ver> 
simple.  If  the  two  adjacent  planes  of  a  crystal  be  successively  brought  into 
the  same  position,  the  angle  through  which  the  crystal  will  have  moved  will 
be  the  supplement  to  that  contained  between  the  two  planes.  This  will  be  easily 
intelligible  by  reference  to  fig.  137,  in  which  a  crystal  having  the  form  of  a 
triangular  prism'  is  shown  in  the  two  positions,  the  angle  to  be  measured 
being  that  indicated  by  the  letters  e  df. 

The  lines  ac,  he,  are  perpendicular  to  the  respective  faces  of  the  crystal, 


•  The  triangular  prism  has  been  chosen  for  the  sake  of  Eimplicity;  but  a  moment's  con- 
sideration will  show  that  the  rule  applies  equally  well  to  any  oUier  figure. 


CHEMISTRY    OT     THE    METALS. 


205 


Fig.  137. 


consequently  the  internal  angles  dgc,  dhc,  are  right  angles.  Now,  since 
the  sum  of  the  internal  angles  of  a  four-sided  rectilineal  figure,  as  dgck, 
equal  four  right  angles,  or  360°,  the  angle  ffdh  (or  e  df)  must  of  necessity 
be  the  supplement  to  the  angle  g  ch,  or  that  through  which  the  crystal 
moves.  All  that  is  required  to  be  done,  therefore,  is  to  measure  the  latter 
angle  with  accuracy,  and  subtract  its  value  from  180° ;  and  this  the  gonio- 
meter effects. 

One  method  of  using  the  instrument  is  the  following : — The  goniometer  is 
placed  at  a  convenient  height  upon  a  steady  table  in  front  of  a  well-illumi- 
nated window.  Horizontally  across  the  latter,  at  the  height  of  eight  or  nine 
feet  from  the  ground,  is  stretched  a  narrow  black  ribbon,  while  a  second 
similar  ribbon,  adjusted  parallel  to  the  first,  is  fixed  beneath  the  window,  a 
foot  or  eighteen  inches  above  the  floor.  The  object  is  to  obtain  too  easily- 
visible  black  lines,  perfectly  parallel.  The  crystal  to  be  examined  is  attached 
to  the  arm  of  the  goniometer  at  /  by  a  little  wax,  and  adjusted  in  such  a 
manner  that  the  edge  joining  the  two  planes  whose  inclination  is  to  be  mea- 
sured shall  nearly  coincide  with,  or  be  parallel  to,  the  axis  of  the  instru- 
ment. This  being  done,  the  adjustment  is  completed  in  the  following  manner: 
— The  divided  circle  is  turned  until  the  zero  of  the  vernier  comes  to  180°  ; 
the  crystal  is  then  moved  round  by  means  of  the  inner  axis  c  (fig.  136)  until 
the  eye  placed  near  it  perceives  the  image  of  the  upper  black  line  reflected 
from  the  surface  of  one  of  the  planes  in  question.  Following  this  image, 
the  crystal  is  still  cautiously  turned  until  the  upper  black  line  seen  by  re- 
flection approaches  and  overlaps  the  lower  black  line  seen  directly  by  another 
portion  of  the  pupil.  It  is  obvious,  that  if  the  plane  of  the  crystal  be  quite 
parallel  to  the  axis  of  the  instrument  (the  latter  being  horizontal),  the  two 
lines  will  coincide  completely.  If,  however,  this  should  not  be  the  case,  the 
crystal  must  be  moved  upon  the  wax  until  the  two  lines  fall  in  one  when  su- 
perposed. The  second  face  of  the  crystal  must  then  be  adjusted  in  the  same 
manner,  care  being  taken  not  to  derange  the  position  of  the  first.  When  by 
repeated  observation  it  is  found  that  both  have  been  correctly  placed,  so  as 
to  bring  the  edge  into  the  required  condition  of  parallelism  with  the  axis  of 
motion,  the  measurement  of  the  angle  may  be  made. 

For  this  purpose  the  crystal  is  moved  as  before  by  the  inner  axis  until  the 
image  of  the  upper  line,  reflected  from  the  first  face  of  the  crystal,  covers 
the  lower  line  seen  directly.  The  great  circle,  carrying  the  whole  with  it, 
is  then  cautiously  turned  until  the  same  coincidence  of  the  upper  with  the 
lower  line  is  seen  by  means  of  the  second  face  of  the  crystal;  that  is,  the 
^  second  face  is  brought  into  exactly  the  same  position  as  that  previously 
occupied  by  the  first.  Nothing  then  remains  but  to  read  off  by  the  vernier 
the  angle  through  which  the  circle  has  been  moved  in  this  operation.  The 
division  upon  the  circle  itself  is  very  often  made  backwards,  so  that  the 
18 


206 


CHEMISTRY    OF    THE    METALfl. 


angle  of  motion  is  not  obtained,  but  its  supplement,  or  the  angle  of  thfe 
crystal  required. 

It  may  be  necessary  to  remark,  that,  although  the  principle  of  the  opera- 
tion described  is  in  the  highest  degree  simple,  its  successful  practice  requires 
considerable  skill  and  experience. 

If  a  crystal  of  tolerably  simple  form  be  attentively  considered,  it  will  be- 
come evident  that  certain  directions  can  be  pointed  out  in  which  straight 
lines  may  be  imagined  to  be  drawn,  passing  through  the  central  point  of  the 
'rystal  from  side  to  side,  from  end  to  end,  or  from  one  angle  to  that  opposed 
o  it,  &c.,  about  which  lines  the  particles  of  matter  composing  the  crystal 
may  be  conceived  to  be  symmetrically  built  up.  Such  lines  or  axes  are  not 
always  purely  imaginary,  however,  as  may  be  inferred  from  the  remarkable 
optical  properties  of  many  crystals ;  upon  their  number,  relative  lengths, 
position,  and  inclination  to  each  other,  depends  the  outward  figure  of  the 
crystal  itself. 

All  crystalline  forms  may  upon  this  plan  be  arranged  in  six  classes  or 
tystems  ;  these  are  as  follows :  — 

1.  The  regular  system. — The  crystals  of  this  division  have  three  equal  axes, 
all  placed  at  right  angles  to  each  other.  The  most  important  forms  are  the 
cube  (1),  the  regular  octahedron  (2),  and  the  rhombic  dodecahedron  (3). 

The  letters  a — a  show  the  terminations  of  the  three  axes,  placed  as  stated. 


Very  many  substances,  both  simple  and  compound,  assume  these  forms,  as 
most  of  the  metals,  carbon  in  the  state  of  diamond,  common  salt,  iodide  of 
potassium,  the  alums,  fluor-spar,  bisulphide  of  iron,  garnet,  spinelle,  &c. 

2.  The  square  prismatic  system.  —  Three  axes  are  here  also  observed,  at 
right-angles  to  each  other.  Of  these,  however,  two  only  are  of  equal  length, 
the  third  being  usually  longer  or  shorter.  The  most  important  forms  are : 
a  right  square  prism,  in  which  the  latter  axes  terminate  in  the  central  point 

Fig.  139. 


-4 y 

''"tt'  / 

a— a.  Principal,  or  vertical  axis. 
b — 6.  Secondary,  or  lateral  axis. 


CHEMISTRY    OF    THE    METALS. 


207 


of  each  side  (1) ;  a  second  right  square  prism,  in  which  the  axes  terminate  in 
the  edges  (2) ;  a  corresponding  pair  of  rir/ht  square-based  octahedra  (3  and  4). 

Examples  of  these  forms  are  to  be  found  in  zircon,  native  binoxide  of  tin, 
apophyllite,  yellow  ferrocyanide  of  potassium,  &c. 

3.  The  right  prismatic  system.  —  This  is  characterized  by  three  axes  of  un- 
equal lengths,  placed  at  right-angles  to  each  other,  as  in  the  right  rectangular 
prism  (1),  the  right  rhombic  prism  (2),  the  right  rectangular-based  octahedron^ 
(3),  and  the  right  rhombic-based  octahedron  (4). 

Fig.  140. 


a — a.  Principal  axis. 

h — b,  c — c.  Secondary  axes. 

The  system  is  exemplified  in  sulphur  crystalliied  at  a  low  temperature, 
arsenical  iron  pyrites,  nitrate  and  sulphate  of  potassa,  sulphate  of  baryta,  &c. 

4.  The  oblique  prismatic  system. — Crystals  belonging  to  this  group  have  also 
three  axes  which  may  be  all  unequal,  two  of  these  (the  secondary)  are  placed 
at  right  angles,  the  third  being  so  inclined  as  to  be  oblique  to  one  and  per- 
pendicular to  the  other.     To  this  system  may  be  referred  the  four  following 

Fig.  141. 


a — a.  Principal  axis. 

6 — 6,  c  c.  Secondary  axes. 

forms: — The  oblique  rectangular  prism  (1),  the  oblique  rhombic  prism  (2),  the 
oblique  rectangular-based  octahedron  (3),  the  oblique  rhombic-based  octahe- 
dron (4). 

Such  forms  are  taken  by  sulphur  crystallized  by  fusion  and  cooling,  real- 
gar, sulphate,  carbonate  and  phosphate  of  soda,  borax,  green  vitriol,  and 
many  other  salts. 

5.  The  doubly-oblique  prismatic  system. — The  crystalline  forms  comprehended 
in  this  division  are,  from  their  great  apparent  in'egularity,  exceedingly  dif- 
ficult to  studv  and  understand.     In  them  are  traced  three  axes,  which  may 


208 


CHEMISTRY     OP     THE    METALS, 


be  all  unequal  in  length,  and  are  all  oblique  to  each  other,  as  in  the  two 
doubly -oblique  prisms  (1  and  2),  and  in  the  corresponding  doubly-oblique  octa- 
hedrons (3  and  4). 

Fig.  142. 


a — a.  Principal  axis,  as  before. 
6 — &,  c — c.  Secondary  axes. 

Sulphate  of  copper,  nitrate  of  bismuth,  and  quadroxalate  of  potassa,  afford 
illustrations  of  these  forms. 

6.  The  rhombohedral  system. — This  is  very  important  and  extensive :  it  is 
characterized  by  the  presence  o^  four  axes,  three  of  which  are  equal,  in  the 
same  plane,  and  inclined  to  each  other  at  angles  of  60°,  while  the  fourth  or 

Fig.  143. 


a — a.  Principal  axis, 
6 — 6.  Secondary  axes. 

principal  axis  is  perpendicular  to  all.  The  regular  six-sided  prism  (1),  thb 
quartz-dodecahedron  (2),  the  rhombohedron  (3),  and  a  second  dodecahedron, 
whose  faces  are  scalene  triangles  (4),  belong  to  the  system  in  question. 

Examples  are  readily  found ;  as  in  ice,  calcareous  spar,  nitrate  of  soda, 
beryl,  quartz  or  rock  crystal,  and  the  semi-metals,  arsenic,  antimony,  and 
tellurium. 

If  a  crystal  increase  in  magnitude  by  equal  additions  on  every  part,  it  is 
quite  clear  that  its  figure  must  remain  unaltered ;  but,  if  from  some  cause 
this  increase  should  be  partial,  the  newly-deposited  matter  being  distributed 
unequally,  but  still  in  obedience  to  certain  definite  laws,  then  alterations  of 
form  are  produced,  giving  rise  to  figures  which  have  a  direct  geometrical 
connection  with  that  from  which  they  are  derived.  If,  for  example,  in  the 
cube,  a  regular  omission  of  successive  rows  of  particles  of  matter  in  a  cer- 
tain order  be  made  at  each  solid  angle,  while  the  crystal  continues  to  increase 
elsewhere,  the  result  will  be  the  production  of  small  triangular  planes, 


CHEiMISTRY    OF    THE    METALS. 


209 


■which,  as  the  process  advances,  gradually  usurp  the  whoTe  of  the  surface  of 
the  crystal,  and  convert  the  cube  into  an  octahedron.  The  new  planes  are 
called  secondary,  and  their  production  is  said  to  take  place  by  regular  decre- 
ments upon  the  solid  angles.  The  same  thing  may  happen  on  the  edges  of 
the  cube ;  a  new  figure,  the  rhombic  dodecahedron,  is  then  generated.  Fig. 
144.  The  modifications  which  can  thus  be  produced  of  the  original  or 
primary  figure  (all  of  which  are  subject  to  exact  geometrical  laws)  are  very 
numerous.  Several  distinct  modifications  may  be  present  at  the  same  time, 
and  thus  render  the  form  exceedingly  complex. 

Fig.  144. 


Passage  of  cube  to  octahedron. 

It  is  important  to  observe,  that  in  all  these  deviations  from  what  may  be 
regarded  as  the  primary  or  fundamental  figure  of  the  crystal,  the  modifying 
planes  are  in  fact  the  planes  of  figures  belonging  to  the  same  natural  group  or 
crystallographical  system  as  the  primary  form,  and  having  their  axes  coincident 
with  those  of  the  latter.  The  crystals  of  each  system  are  thus  subject  to  a 
peculiar  and  distinct  set  of  modifications,  the  observation  of  which  very 
frequently  constitutes  an  excellent  guide  to  the  discovery  of  the  primary 
form  itself. 

Crystals  often  cleave  parallel  to  all  the  planes  of  the  primary  figure,  as  in 
calcareous  spar,  which  offers  a  good  illustration  of  this  perfect  cleavage. 
Sometimes  one  or  two  of  these  planes  have  a  kind  of  preference  over  the 
rest  in  this  respect,  the  crystal  splitting  readily  in  these  directions  only. 

A  very  curious  modification  of  the  figure  sometimes  occurs  by  the  exces- 
sive growth  of  each  alternate  plane  of  the  crystal ;  the  rest  become  at  length 
obliterated,  and  the  crystal  assumes  the  character  called  hemihedral  or  half- 
sided.  This  is  well  seen  in  the  production  of  the  tetraliedron  from  the  regular 
octahedron  (fig.  145),  and  of  the  rhombohedric  form  by  a  similar  change 
from  the  quartz-dodecahedron  already  figured. 

Fig.  145. 


Passage  of  octahedron  to  tetrahedron. 

Relations  of  form  and  constitution  ;  Isomorphism.  —  Certain  substances  to 
which  a  similar  chemical  constitution  is  ascribed,  possess  the  remarkable 
property  of  exactly  replacing  each  other  in  crystallized  compounds  without 
alteration  of  the  characteristic  geometrical  figure.  Such  bodies  are  said  to 
be  isomorphous.^ 


18 


From  7(705,  equal,  and  u6p(}>Tt,  shape  or  form. 


210  CHEMISTRY    OP    THE    METALS. 

For  example,  magnesia,  oxide  of  zinc,  oxide  of  copper,  protoxide  of  iron, 
and  oxide  of  nickel,  are  allied  by  isomorphic  relations  of  the  most  intimate 
nature.  The  salts  formed  by  these  substances  with  the  same  acid  and 
similar  proportions  of  water  of  crystallization,  are  identical  in  their  form, 
and,  when  of  the  same  colour,  cannot  be  distinguished  by  the  eye  ;  the  sul- 
phates of  magnesia  and  zinc  may  be  thus  confounded.  The  sulphates,  too, 
all  combine  with  sulphate  of  potassa  and  sulphate  of  ammonia,  giving  rise 
to  double  salts,  whose  figure  is  the  same,  but  quite  different  from  that  of  the 
simple  sulphates.  Indeed,  this  connection  between  identity  of  form  and 
parallelism  of  constitution  runs  through  all  their  combinations. 

In  the  same  manner,  alumina  and  sesquioxide  of  iron  replace  each  other 
continually  without  change  of  crystalline  figure  ;  the  same  remark  may  be 
made  of  potassa,  soda,  and  ammonia,  with  an  equivalent  of  water,  or  oxide 
of  ammonium,  these  bodies  being  strictly  isomorphous.  The  alumina  in 
in  common  alum  may  be  replaced  by  sesquioxide  of  iron ;  the  potassa  by 
ammonia,  or  by  soda,  and  still  the  figure  of  the  crystal  remains  unchanged. 
These  replacements  may  be  partial  only ;  we  may  have  an  alum  containing 
both  potassa  and  ammonia,  or  alumina  and  sesquioxide  of  chromium.  By 
artificial  management,  namely,  by  transferring  the  crystal  successively  to 
different  solutions,  we  may  have  these  isomorphous  and  mutually  replacing 
compounds  distributed  in  different  layers  upon  the  same  crystal. 

For  these  reasons,  mixtures  of  isomorphous  salts  can  never  be  separated 
by  crystallization,  unless  their  difference  of  solubility  is  very  great.  A 
mixed  solution  of  sulphate  of  protoxide  of  iron  and  sulphate  of  copper,  iso- 
morphous salts,  yields  on  evaporation  crystals  containing  both  iron  and 
copper.  But  if  before  evaporation  the  protoxide  of  iron  be  converted  into 
sesquioxide  by  chlorine  or  other  means,  then  the  crystals  obtained  are  free 
from  iron,  except  that  of  the  mother-liquor  which  wets  them.  The  salt  of 
sesquioxide  of  iron  is  no  longer  isomorphous  with  the  copper  salt,  and  easily 
separates  from  the  latter. 

When  compounds  are  thus  found  to  correspond,  it  is  inferred  that  the  ele- 
ments composing  them  are  also  isomorphous.  Thus,  the  metals  magnesium, 
zinc,  iron,  and  copper  are  presumed  to  be  isomorphous ;  arsenic  and  phos- 
phorus should  present  the  same  crystalline  form,  because  arsenic  and  phos- 
phoric acids  give  rise  to  combinations  which  agree  most  completely  in  figure 
and  constitution.  The  chlorides,  iodides,  bromides,  and  fluorides,  agree, 
whenever  they  can  be  observed,  in  the  most  perfect  manner ;  hence  the  ele- 
ments themselves  are  believed  to  be  also  isomorphous.  Unfortunately,  for 
obvious  reasons,  it  is  very  difficult  to  observe  the  crystalline  figure  of  most 
of  the  elementary  bodies,  and  this  difficulty  is  increased  by  the  frequent  di- 
morphism they  exhibit. 

Absolute  identity  of  value  in  the  angles  of  crystals  is  not  always  exhibited 
by  isomorphous  substances.  In  other  words,  small  variations  often  occur 
in  the  magnitude  of  the  angles  of  crystals  of  compounds  which  in  all  other 
respects  show  the  closest  isomorphic  relations.  This  should  occasion  no 
surprise,  as  there  are  reasons  why  such  variations  may  be  expected,  the 
chief  perhaps  being  the  unequal  effects  of  expansion  by  heat,  by  which  the 
angles  of  the  same  crystals  are  changed  by  alteration  of  temperature.  A 
good  example  is  found  in  the  case  of  the  carbonates  of  lime,  magnesia,  man- 
ganese, iron,  and  zinc,  which  are  found  native  crystallized  in  the  form  of 
obtuse  rhombohedra  (fig.  143,  3)  not  distinguishable  from  each  other  by  the 
eye,  or  even  by  the  common  goniometer,  but  showing  small  differences  when 
examined  by  the  more  accurate  instrument  of  Dr.  Wollaston,  These  com- 
pounds are  isomorphous,  and  the  measurements  of  the  obtuse  angles  of  theii 
rhombohedra  as  follows : — 


CHEMISTRY     OF     THE    METALS. 


211 


Carbonate  of  lime 105°    5-' 

"  magnesia 107°  25'' 

"  protox.  manganese 107°  20^ 

"  "       iron 107° 

"  zinc 107°  40^ 

Anomalies  in  the  composition  of  various  earthy  minerals  which  formerly 
threw  much  obscurity  upon  their  chemical  nature,  have  been  in  great  mea- 
sure explained  by  these  discoveries. 

Specimens  of  the  same  mineral  from  different  localities  were  found  to 
afford  very  discordant  results  on  analysis.  But  the  proof  once  given  of  the 
extent  to  which  substitution  of  isomorphous  bodies  may  go  without  destruc- 
tion of  what  may  be  called  the  primitive  type  of  the  compound,  these  diffi- 
culties vanish. 

Another  benefit  conferred  on  science  by  the  discoveries  in  question,  is 
that  of  furnishing  a  really  philosophical  method  of  classifying  elementary 
and  compound  substances,  so  as  to  exhibit  their  natural  relationships;  it 
would  be  perhaps  more  proper  to  say  that  such  will  be  the  case  when  the 
isomorphic  relations  of  all  the  elementary  bodies  become  known, — at  present 
only  a  certain  number  have  been  traced. 

Decision  of  a  doubtful  point  concerning  the  constitution  of  a  compound 
may  now  and  then  be  very  satisfactorily  made  by  a  reference  to  this  same 
law  of  isomorphism.  Thus,  alumina,  the  only  known  oxide  of  aluminium, 
is  judged  to  be  a  sesquioxide  of  the  metal  from  its  relation  to  sesquioxide 
of  iron,  which  is  certainly  so ;  the  black  oxide  of  copper  is  inferred  to  be 
really  the  protoxide,  although  it  contains  twice  as  much  oxygen  as  the  red 
oxide,  because  it  is  isomorphous  with  magnesia  and  zinc,  both  undoubted 
protoxides. 

The  subjoined  table  will  serve  to  convey  some  idea  of  the  most  important 
families  of  isomorphous  elements ;  it  is  taken  from  Professor  Graham's  sys- 
tematic work,'  to  which  the  pupil  is  referred  for  fuller  details  on  this  inte 
resting  subject. 

liomoTjphous  Groups. 

(1.)  (3.)                               (7.) 

Sulphur  Barium  Sodium 

Selenium  Strontium  Silver 

Tellurium.  Lead.  Gold 

(2.)  (4.)  Potassium 

Magnesium  Tin  Ammonium. 

Calcium  Titanium.                        (8.) 

Manganese  (5.)  Chlorine 

Iron  Platinum  Iodine 

Cobalt  Iridium  Bromine 

Nickel  Osmium.  Fluorine 

Zinc  (6.)  Cyanogen. 

Cadmium  Tungsten                            (9.) 

Copper  Molybdenum  Phosphorus 

Chromium  Tantalum.  Arsenic 

Aluminium  Antimony 

Beryllium  BismuthI 
Vanadium 
Zirconium. 

There  is  a  law  concerning  the  formation  of  double  salts  which  may  now 
be  mentioned ;  the  two  bases  are  never  taken  from  the  same  isomorphous 

'  Second  edition,  p.  149. 


212  CHEMISTRY    OP    THE     METALS. 

family.  Sulphate  of  copper  or  of  zinc  may  unite  in  this  manner  with  sulphate 
of  soda  or  potassa,  but  not  with  sulphate  of  iron  or  cobalt ;  chloride  of  mag- 
nesium may  combine  with  chloride  of  ammonium,  but  not  with  chloride  of 
zinc  or  nickel,  &c.  It  will  be  seen  hereafter  that  this  is  a  matter  of  some 
importance  in  the  theory  of  the  organic  acids. 

Polybasic  Acids.  —  There  is  a  particular  class  of  acids  in  which  a  departure 
occurs  from  the  law  of  neutrality  formerly  described ;  these  are  acids  re- 
quiring two  or  more  equivalents  of  a  base  for  neutralization.  The  phosphoric 
and  arsenic  acids  present  the  best  examples  yet  known  in  mineral  chemistry, 
but  in  the  organic  department  of  the  science  cases  very  frequently  occur. 

Phosphoric  acid  is  capable  of  existing  in  three  different  states  or  modifica- 
tions, forming  three  separate  classes  of  salts  which  differ  completely  in  pro- 
perties and  constitution.  They  are  distinguished  by  the  names  trihasic, 
bibasic,  and  monobasic  acids,  according  to  the  number  of  equivalents  of  base 
required  to  form  neutral  salts. 

Tribasic  or  Comvion  Phosphoric  Acid,  — When  commercial  phosphate  of  soda 
is  dissolved  in  water  and  the  solution  mixed  with  acetate  of  lead,  an  abundant 
white  precipitate  of  phosphate  of  lead  falls,  which  may  be  collected  on  a 
filter,  and  well  washed.  While  still  moist,  this  compound  is  suspended  in 
distilled  water,  and  an  excess  of  sulphuretted  hydrogen  gas  passed  into  it. 
The  protoxide  of  lead  is  converted  into  sulphide,  which  subsides  as  a  black 
insoluble  precipitate,  while  phosphoric  acid  remains  in  solution,  and  is  easily 
deprived  of  the  residual  sulphuretted  hydrogen  by  a  gentle  heat. 

The  soda-salt  employed  in  this  experiment  contains  the  tribasic  modifica- 
tion of  phosphoric  acid ;  of  the  three  equivalents  of  base,  two  consist  of  soda 
and  one  of  water  ;  when  mixed  with  solution  of  lead,  a  tribasic  phosphate  of 
the  oxide  of  that  metal  falls,  which  when  decomposed  by  sulphuretted  hydro- 
gen, yields  sulphide  of  lead  and  a  hydrate  of  the  acid  containing  three 
equivalents  of  water  in  intimate  combination. 

f  2  eq.  soda — y  2  eq.  acetate  of  soda. 

Phosphate       J  1   »  water y  y^  "    ^y Crated  acetic  acid. 

of  soda  1  1    ,,  phos-l 

[  phoric  acid  / 

Q  ^^   ..««*„*«  r  2  eq.  acetic  acid' 
3  eq.  acetate  1  ^   ^  ^^^^..^  ^^^^. 

""^  ^^^^       1 3  ',;  oxide  of  lead ^^  ^  e^-  tribasic  phosphate 

^  of  lead. 

{3  eq.  lead  . 7  3  eq.  sulphide  of  lead. 
3   „    oxygen 
1    „  phos- 
phoric acid 
3   eq.    sulphuretted    f  3  eq.  sulphur' 

hydrogen  t  3  ,,    hydrogen ^^  1  eq.  tribasic  hydrate  of 

phosphoric  acid. 

The  solution  of  tribasic  hydrate  may  be  concentrated  by  evaporation  in 
vacuo  over  sulphuric  acid  until  it  crystallizes  in  thin  deliquescent  plates. 
The  same  compound  in  beautiful  crystals,  resembling  those  of  sugar-candy, 
has  been  accidentally  formed.'  It  undergoes  no  change  by  boiling  with 
water,  but  when  heated  alone  to  400°  (204°-4C)  loses  some  of  its  combined 
water,  and  becomes  converted  into  a  mixture  of  the  bibasic  and  monobasic 
hydrates.  At  a  red  heat  it  becomes  entirely  changed  to  monohydrate,  which, 
at  a  still  higher  temperature,  sublimes. 

Tribasic  phosphoric  acid  is  characterized  by  the  yellow  insoluble  salt  it 
forms  with  protoxide  of  silver. 

» Peligot,  Ano.  Cbim.  et  Pbys.  Ixxiii.  286. 


OHEMISTEY    OP    THB    METALS.  218 

Bibasi*  Phosphoric  Acid^  or  Pyrophosphoric  Acid.  —  When  common  phos- 
phate of  soda,  containing 

2NaO,  HO,  POg-f  24HO, 
is  gently  heated,  the  24  equivalents  of  water  of  crystallization  are  expelled, 
and  the  salt  becomes  anhydrous ;  but  if  the  heat  be  raised  to  a  higher  point, 
the  basic  water  is  also  driven  off,  and  the  acid  passes  into  the  second  or 
bibasic  modification.  If  the  altered  salt  be  now  dissolved  in  water,  this  new 
compound,  the  bibasic  phosphate  of  soda,  crystallizes  out.  When  mixed  with 
solution  of  acetate  of  lead,  bibasic  phosphate  of  lead  is  thrown  down,  which, 
decomposed  by  sulphuretted  hydrogen,  furnishes  a  solution  of  the  bibasio 
hydrate.  This  solution  may  be  preserved  without  change  at  common  tem- 
peratures, but  when  heated,  an  equivalent  of  water  is  taken  up,  and  tho 
substance  passes  back  again  into  the  tribasic  modification. 

Crystals  of  this  hydrate  have  also  been  observed  by  M.  P^ligot.  Their 
production  was  accidental.  The  bibasic  phosphates  soluble  in  water  give  a 
white  precipitate  with  solution  of  silver. 

Monobasic,  or  Metaphosphoric  Add.  —  When  common  tribasic  phosphate  of 
Boda  is  mixed  with  solution  of  tribasic  hydrate  of  phosphoric  acid,  and  ex- 
posed, after  proper  concentration,  to  a  low  temperature,  prismatic  crystals 
are  obtained,  which  consist  of  a  phosphate  of  soda  having  two  equivalents  of 
basic  water. 

NaO,  2H0,  PO5+2HO. 

When  this  salt  is  very  strongly  heated,  both  the  water  of  crystallization 
and  that  contained  in  the  base  are  expelled,  and  monobasic  phosphate  of 
soda  remains.  This  may  be  dissolved  in  cold  water,  precipitated  with  ace- 
tate of  lead,  and  the  lead-salt,  as  before,  decomposed  by  sulphuretted  hy- 
drogen. 

The  solution  of  the  monobasic  hydrate  is  decomposed  rapidly  by  heat, 
becoming  converted  into  tribasic  hydrate.  It  possesses  the  property  of  co- 
agulating albumen,  which  is  not  enjoyed  by  either  of  the  preceding  modifi- 
cations.    Monobasic  alkaline  phosphates  precipitate  nitrate  of  silver  white. 

The  glacial  phosphoric  acid  of  pharmacy  is,  when  pure,  hydrate  of  mono- 
basic phosphoric  acid :  it  contains  HO,  PO5. 

Anhydrous  phosphoric  acid,  prepared  by  burning  phosphorus  in  dry  air, 
when  thrown  into  water,  forms  a  variable  mixture  of  the  three  hydrates. 
When  heated,  a  solution  of  the  tribasic  hydrate  alone  remains.*  See  also 
phosphates  of  soda. 

Binary  Theory  of  Salts. — The  great  resemblance  in  properties  between  the 
two  classes  of  saline  compounds,  the  haloid  and  oxy-salts,  has  very  naturally 
led  to  the  supposition  that  both  might  possibly  be  alike  constituted,  and  that 
the  latter,  instead  of  being  considered  compounds  of  an  oxide  and  an  acid, 
might  with  greater  propriety  be  considered  to  contain  a  metal  in  union  with 
a  compovmd  salt-radical,  having  the  chemical  relations  of  chlorine  and 
iodine. 

On  this  supposition  sulphate  and  nitrate  of  potassa  will  be  constituted  in 
the  same  manner  as  chloride  of  potassium,  the  compound  radical  replacing 
the  simple  one. 

Old  view.  New  view. 

KO4-SO3  K-f-SO^ 

KO-f-NOg  K-fNOg 

*  The  three  modifications  of  phosphoric  acid  possess  properties  so  dissimilar  that  they  might 
really  be  considered  three  distinct,  although  intimately  related  bodies.  It  is  exceedingly 
remarkable,  that  when  their  salts  are  subjected  to  electro-chemical  decomposition,  the  acidi 
travel  unaltered,  a  tribasic  salt  giving  at  the  positive  electrode  a  solution  of  common  pho9. 
phoric  acid;  a  bibasic  salt,  one  of  pyrophosphoric  acid  ;  and  a  monobasic  salt,  one  of  met» 
phosphoric  acid  (Professor  Daniell  and  Dr.  Miller,  Phil.  Trans,  for  1844,  p.  1). 


214  CHEMISTRY    OP    THE    METALS. 

Hydrated  sulphnric  acid  will  be,  like  hydrochloric  acid,  a  hydride  of  a  salt- 
radical, 

H+SO4. 

When  the  latter  acts  upon  metallic  zinc,  the  hydrogen  is  simply  displaced, 
and  the  metal  substituted ;  no  decomposition  of  water  is  supposed  to  occur, 
and,  consequently,  the  difficulty  of  the  old  hypothesis  is  at  an  end.  When 
the  acid  is  poured  upon  a  metallic  oxide,  the  same  reaction  occurs  as  in  the 
case  of  hydrochloric  acid,,  water  and  a  haloid  salt  are  produced.  All  acids 
must  be,  in  fact,  hydrogen  acids,  and  all  salts  haloid  salts,  with  either  simple 
or  compound  radicals. 

This  simple  and  beautiful  theory  is  not  by  any  means  new ;  it  was  sug- 
gested by  Davy,  who  proposed  to  consider  hydrogen  as  the  acidifying  prin- 
ciple in  the  common  acids,  and  lately  revived  and  very  happily  illustrated  by 
Liebig.  It  is  supported  by  a  good  deal  of  evidence  derived  from  various 
sources,  and  has  received  great  help  from  a  series  of  exceedingly  interesting 
experiments  on  the  electrolysis  of  saline  solutions,  by  the  late  Professor 
Daniell.*  The  necessity  of  creating  a  great  number  of  non-insoluble  com- 
pounds is  often  urged  as  an  objection  to  the  new  view ;  but  the  same  objec- 
tion applies  to  the  old  mode  of  considering  the  subject.  Hyposulphurous 
acid  and  hyposulphuric  acid  are  unknown  in  their  free  states.  The  com- 
pounds SgOg  and  S2O4  are  as  hypothetical  as  the  substances  SjOg  and  SjOg. 
The  same  remark  applies  to  almost  every  one  of  the  organic  acids  ;  and,  what 
is  well  worthy  of  notice,  those  acids  which,  like  sulphuric,  phosphoric,  and 
carbonic  acids,  may  be  obtained  in  a  separate  state,  are  destitute  of  all  acid 
jproperties  so  long  as  the  anhydrous  condition  is  retained. 

Some  very  interesting  observations  have  been  published  lately  by  M.  Ger- 
hardt,»  which  are  likely  to  hasten  a  change  in  the  notation  of  acids  generally. 

It  has  been  pointed  out  that  sulphuric  and  nitric  acid,  which,  according 
to  the  theory  of  oxygen  acids,  are  considered  as  compounds  respectively  of 
teroxide  of  sulphur  and  pentoxide  of  nitrogen  with  water,  SOg,!!©,  and  NO5, 
HO,  may  be  considered  likewise  as  hydrogen  acids,  analogous  to  hydro- 
chloric and  hydrocyanic  acid. 

Hydrochloric  acid  HCl 

Hydrocyanic  acid  HCaN 

Sulphuric  acid  \  ttoq 

Hydrosulphanic  acid  j  * 

Nitric  acid  S    HNO«. 

Hydronitranic  acid..  / 

Among  the  many  facts  which  have  been  adduced  in  favour  of  the  theory 
of  oxygen  acids,  the  preparation  of  the  so-called  anhydrous  acids  SO,  and 
NOs  (see  pages  124  and  135)  has  always  been  considered  as  powerful  props. 
On  the  other  hand,  the  followers  of  the  theory  of  hydrogen  acids  have  inva- 
riably called  attention  to  the  scarcity  of  the  so-called  anhydrous  acids,  and 
especially  to  the  fact  that,  with  a  few  exceptions,  they  are  entirely  wanting 
in  Organic  Chemistry.  The  researches  of  ]M.  Gerhardt  just  referred  to, 
have  furnished  the  means  of  making  the  anhydrous  organic  acids ;  but  the 
circumstances  under  which  they  are  produced  exhibit  these  substances  in  a 
perfectly  new  light,  and  prove  that  they  stand  in  a  very  diflferent  relation  to 
the  hydrated  acids  from  what  is  generally  assumed. 

If  dry  benzoate  of  soda  be  heated  with  chloride  of  benzoyl  (see  page  399) 
to  a  temperature  of  266°  (130°C),  a  limpid  liquid  is  formed,  which  is  de- 

'  See  Danieirs  Introduction  to  Chemical  Philosophy,  2d  edition,  p.  533. 
•  Chem.  Soc.  Quar.  Jour.  v.  127. 


CHEMISTRY    OF    THE     METALS.  215 

composed  with  deposition  of  chloride  of  sodium  when  heated  a  few  degrees 
higher ;  there  is  formed,  at  the  same  time,  a  white  crystalline  product, 
which  has  exactly  the  composition  of  anhydrous  benzoic  acid,  for  it  contains 
CwHgOj  or  BzO,  if  we  represent  C14H5O3  by  Bz.  The  decomposition  which 
takes  place  is  represented  by  the  following  equation : — 
B20,NaO+BzCl=:NaCl+2BzO. 

The  new  substance  crystallizes  in  beautiful  oblique  prisms,  fusible  at  90°  -4 
(33°C),  and  volatile  without  decomposition.  It  is  insoluble  in  water,  but 
readily  dissolves  in  alcohol  and  ether ;  these  solutions  are  perfectly  neutral  to 
test-paper.  Cold  water  has  not  the  slightest  effect  upon  this  body ;  by  boil- 
ing water  it  is  gradually  converted  into  benzoic  acid.  This  change  immedi- 
ately occurs  with  boiling  solutions  of  the  alkalis.  Boiling  alcohol  converts 
it  into  benzoate  of  ethyl.  From  the  mode  of  formation,  it  is  evident  that 
the  substance  in  question  cannot  be  regarded  as  anhydrous  benzoic  acid,  al- 
though it  agrees  with  that  substance  in  composition.  It  is  obviously  a  sort 
of  a  salt,  benzoate  of  benzoyl,  or  benzoic  acid  in  which  one  equivalent  of  hy- 
drogen is  replaced  by  benzoyl. 

Benzoic  acid BzO,HO 

New  compound  BzO,BzO. 

If  an  additional  support  for  this  view  was  required,  it  would  be  found  in 
the  circumstance  that  chloride  of  benzoyl  acts  in  exactly  the  same  manner 
upon  cumate,  cinnamate,  and  salicylate  of  soda,  a  series  of  compounds  be- 
ing produced  which  are  perfectly  analogous  to  the  preceding  substance,  but 
contain  in  the  place  of  benzoyl  cuminyl,  CaoHi203=Cm ;  cinnamyl,  CigH^O'zss 
Ci;  or  salicyl,  CuS50i=:Sl. 

Benzoic  acid BzO,HO 

Benzoate  of  benzoyl  BzO,BzO 

Benzoate  of  cuminyl BzO,CmO 

Benzoate  of  cinnamyl  BzO,CiO 

Benzoate  of  salicyl BzO,S10. 

These  substances  are  for  the  most  part  fusible,  odourless  solids,  or  oils 
heavier  than  water.  With  the  alkalis  they  yield  a  mixture  of  the  acids  from 
which  they  have  been  produced.  Several  are  not  volatile  without  decompo- 
sition. 

A  perfectly  similar  series  of  substances  has  been  obtained  with  acetic  acid. 
The  acetic  chloride,  CIC4H3O2,  corresponding  to  chloride  of  benzoyl,  is  formed 
in  a  most  interesting  process,  namely,  by  the  action  of  pentachloride  of 
phosphorus  (see  page  168)  upon  acetate  of  soda,  when  chloride  of  sodium, 
oxichloride  of  phosphorus,  PCI3O3,  and  chloride  of  acetetyP  are  formed. 
NaO,C4H303+Pa5=NaCl-fPCl302-fC4H302Cl. 

The  action  of  chloride  of  acetttyl  upon  dry  acetate  of  soda  gives  rise  to 
the  formation  of  an  oily  liquid,  which  has  the  composition  of  anhydrous 
acetic  acid,  C^HgOg,  but  which  in  reality  is  acetate  of  acetetyl  =  C4H.,02, 
04H3O2,O.'     This  liquid  boils  at  278°-6  (137°C) ;  it  is  not  miscible  at  once 

*  Acetetyl  in  order  to  distinguish  it  from  acetyl,  C4HS. 

'  This  formula  requires  an  equivalent  of  oxygen  to  produce  two  equivalents  of  anhydrous 
acetic  acid. 

C4H903,C4H3O2O  +  O=2(C4H3O3,O). 

In  the  reaction  hetween  acetate  of  soda  and  chloride  of  acetyle,  an  equivalent  of  oxygen  from 
the  soda  converts  the  acetetyl  into  anhydrous  acetic  acid  with  the  formation  of  chloride  of 
sodium. 

NaO.C4H308 + G4H  j03Cl=2(C4H303) + NaCl. 
Acetetyle  here  spoken  of,  is  from  its  composition  acetous  or  aldehydic  add.  — R.  B. 


216  CHEMISTRY    OP    THE    METALS. 

with  cold  water,  but  only  after  continued  agitation.  Hot  water  dissolves  it 
at  once  with  formation  of  acetic  acid. 

The  application  to  inorganic  compounds  of  the  method,  by  means  of  which 
these  substances  are  produced,  promises  in  future  very  important  materials 
for  the  elaboration  of  several  of  the  most  interesting  questions  with  which 
chemists  are  engaged  at  the  present  moment. 

The  general  application  of  the  binary  theory  still  presents  a  few  difficul- 
ties. But  it  is  very  probable  that  the  progress  of  discovery  will  ultimately 
lead  to  its  universal  adoption,  which  would  greatly  simplify  many  parts  of 
the  science.  One  great  inconvenience  will  be  the  change  of  nomenclature 
mvoUed. 


CLASSIFICATION    OF   METALS. 
1. 

Metals  of  the  Alkalis. 
Potassium,  Lithium, 

Sodium,  Ammouiuni. » 

2. 
Metals  of  the  Alkaline  Earths. 
Barium,  Calcium, 

Strontium,  Magnesium. 

3. 
Metals  of  the  Earths  Proper. 
Aluminium,  Norium, 

Beryllium,  Thorium, 

Yttrium,  Cerium, 

Erbium,  Lantanum, 

Terbium,  Didymium. 

Zirconium, 

4. 
Ozidahle  Metals  proper ^  whose  Oxides  form  powerful  Bases. 
Manganese,  ■  Zinc, 

Iron,  Cadmium, 

Chromium,  Bismuth, 

Nickel,  Lead, 

Cobalt,  Uranium. 

Copper, 

5. 
Oxidable  Metals  Proper,  whose  Oxides  form  weak  Bases,  or  Adds. 


Vanadium, 

Titanium, 

Tungsten, 

Molybdenum, 

Tantalum, 

Tin, 
e               Antimony, 
Arsenic, 

Niobium, 

Tellurium, 

Pelopium, 

Osmium. 
6. 

are  reduced  by  Heat ;  Noble  Metals, 

Metals  Proper,  whose  Oxides 

Gold, 

Palladium, 

Mercury, 
Silver, 

Iridium, 
Ruthenium, 

Platinum, 

Rhodium. 

^  /his  hypothetical  substance  is  merely  placed  with  the  metals  for  the  sake  of  couvenlenoe, 
I  «flll  be  apparent  in  the  sequel. 


POTASSIUM.  217 


SECTION  I. 
METALS  OF  THE  ALKALIS. 


POTASSIUM. 

Potassium  was  discovered  by  Sir  H.  Davy  in  1807,  who  obtained  it  in 
very  small  quantity  by  exposing  a  piece  of  moistened  hydrate  of  potassa  to 
the  action  of  a  powerful  voltaic  battery,  the  alkali  being  placed  between  a 
pair  of  platinum  plates  put  into  connection  with  the  apparatus.  Processes 
have  since  been  devised  for  obtaining  this  curious  metal  in  almost  any 
quantity  that  can  be  desired. 

An  intimate  mixture  of  carbonate  of  potassa  and  charcoal  is  prepared  by 
calcining,  in  a  covered  iron  pot,  the  crude  tartar  of  commerce ;  when  cold, 
it  is  rubbed  to  powder,  mixed  with  one-tenth  part  of  charcoal  in  small  lumps, 
and  quickly  transferred  to  a  retort  of  stout  hammered  iron ;  the  latter  may 
be  one  of  the  iron  bottles  in  which  mercury  is  imported,  a  short  and  some- 
what wide  iron  tube  having  been  fitted  to  the  aperture.  The  retort  is  placed 
upon  its  side,  in  a  furnace  so  constructed  that  the  flame  of  a  very  strong 
fire,  fed  with  dry  wood,  may  vrrap  round  it,  and  maintain  every  part  at  an 
uniform  degree  of  heat,  approaching  to  whiteness.  A  copper  receiver, 
divided  in  the  centre  by  a  diaphragm,  is  connected  to  the  iron  pipe,  and  kept 
cool  by  the  application  of  ice,  while  the  receiver  itself  is  partly  filled  with 
naphtha  or  rock-oil,  in  which  the  potassium  is  to  be  preserved.  Arrange 
ments  being  thus  completed,  the  fire  is  gradually  raised  until  the  requisite 
temperature  is  reached,  when  decomposition  of  the  alkali  by  the  charcoal 
commences,  carbonic  oxide  gas  is  abundantly  disengaged,  and  potassium 
distils  over,  and  falls  in  large  melted  drops  into  the  liquid.  The  pieces  of 
charcoal  are  introduced  for  the  purpose  of  absorbing  the  melted  carbonate 
of  potassa,  and  preventing  its  separation  from  the  finely  divided  carbonaceous 
matter. 

If  the  potassium  be  wanted  absolutely  pure,  it  must  be  afterwards  re-dis- 
tilled in  an  iron  retort,  into  which  some  naphtha  has  been  put,  that  its 
vapour  may  expel  the  air,  and  prevent  the  oxidation  of  the  metal. 

Potassium  is  a  brilliant  white  metal,  with  a  high  degree  of  lustre ;  at  the 
common  temperature  of  the  air  it  is  soft,  and  may  be  easily  cut  with  a  knife, 
but  at  32°  (0°C)  it  is  brittle  and  crystalline.  It  meltfe  completely  at  136^' 
(57° -770),  and  distils  at  a  low  red  heat.  The  density  of  this  remarkable 
metal  is  only  0-865,  water  being  unity. 

Exposed  to  the  air,  potassium  oxidizes  instantly,  a  tarnish  covering  the 
surface  of  the  metal,  which  quickly  thickens  to  a  crust  of  caustic  potassa. 
Thrown  upon  water,  it  takes  fire  spontaneously,  and  burns  with  a  beautiful 
purple  flame,  yielding  an  alkaline  solution.  When  brought  into  contact  with 
a  little  water  in  ajar  standing  over  mercury,  the  liquid  is  decomposed  with 
great  energy,  and  hydrogen  liberated.  Potassium  is  always  preserved  under 
the  surface  of  naphtha. 

The  equivalent  of  potassium  (kalium)  is  39  j  and  its  symbol,  K 
19 


2ii 


POTASSIUM. 


There  are  two  compounds  of  this  metal  with  oxygen, — potassa  and  teroxide 
of  potassium. 

Potassa,  Potash,  or  Protoxide  of  Potassium,  KO,  is  produced  when 
potassium  is  heated  in  dry  air ;  the  metal  burns,  and  becomes  entirely  con- 
verted into  a  volatile,  fusible,  white  substance,  which  is  anhydrous  potassa. 
Moistened  with  water,  it  evolves  great  heat,  and  forms  the  hydrate. 

The  hydrate  of  potassa,  KO,  HO,  is  a  very  important  substance,  and  one 
of  great  practical  utility.  It  is  always  prepared  for  use  by  decomposing  the 
4;arbonate  by  hydrate  of  lime,  as  in  the  following  process,  which  is  very  con- 
venient:— 10  parts  of  carbonate  of  potassa  are  dissolved  in  100  parts  of 
water,  and  heated  to  ebullition  in  a  clean  untinned  iron,  or  still  better,  silver 
vessel ;  8  parts  of  good  quicklime  are  meanwhile  slaked  in  a  covered  basin, 
and  the  resulting  hydrate  of  lime  added,  little  by  little,  to  the  boiling  solu- 
tion of  carbonate,  with  frequent  stirring.  When  all  the  lime  has  been  in- 
troduced, the  mixture  is  suffered  to  boil  a  few  minutes,  and  then  removed 
from  the  fire,  and  covered  up.  In  the  course  of  a  very  short  time,  the  solu- 
tion will  have  become  quite  clear,  and  fit  for  decantation,  the  carljonate  of 
lime,  with  the  excess  of  hydrate,  settling  down  as  a  heavy,  sandy  precipi- 
tate.    The  solution  should  not  effervesce  with  acids. 

It  is  essential  in  this  process  that  the  solution  of  carbonate  of  potassa  be 
dilute,  otherwise  the  decomposition  becomes  imperfect ;  the  proportion  of 
lime  recommended  is  much  greater  than  that  required  by  theory,  but  it  is 
always  proper  to  have  an  excess. 

The  solution  of  hydrate,  or,  as  it  is  commonly  called,  caustic  potassa,  may 
be  concentrated  by  quick  evaporation  in  the  iron  or  silver  vessel  to  any 
desired  extent ;  when  heated  until  vapour  of  water  ceases  to  be  disengaged, 
and  then  suffered  to  cool,  it  furnishes  the  solid  hydrate,  containing  single 
equivalents  of  potassa  and  water. 

Pure  hydrate  of  potassa  is  a  white  solid  substance,  very  deliquescent  and 
soluble  in  water ;  alcohol  also  dissolves  it  freely,  which  is  the  case  with  com- 
paratively few  of  the  compounds  of  this  base ;  the  solid  hydrate  of  com- 
merce, which  is  very  impure,  may  thus  be  purified.  The  solution  of  this 
substance  possesses,  in  the  very  highest  degree,  the  properties  termed  alka- 
line ;  it  restores  the  blue  colour  to  litmus  which  has  been  reddened  by  an 
acid ;  neutralizes  completely  the  most  powerful  acids ;  has  a  naseous  and 
peculiar  taste,  and  dissolves  the  skin,  and  many  other  organic  matters,  when 
the  latter  are  subjected  to  its  action.  It  is  constantly  used  by  surgeons  as  a 
cautery,  being  moulded  into  little  sticks  for  that  purpose. 

Hj  irate  of  potassa,  both  in  the  solid  state  and  in  solution,  rapidly  absorbs 
carbonic  acid  from  the  air ;  hence  it  must  be  kept  in  closely  stopped  battles. 
When  imperfectly  prepared,  or  partially  altered  by  exposure,  it  efferreoces 
with  an  acid. 

The  water  in  this  compound  cannot  be  displaced  by  heat,  the  hydrate  vo- 
latilizing as  a  whole  at  a  very  high  temperature. 

The  following  table  of  the  densities  and  value  in  real  alkali  of  different 
"o'lutions  of  hydrate  of  potassa  is  given  on  the  authority  of  Dr.  Dalton. 


_       ,.  Percentage  of 

J^ensity.  real  alkali. 


1-68  51-2 

1-60  46-7 

162  42  9 

1-47  39-6 

1-44  36  8 

1-42  34-4 

1-39  32-4 

1-36  29-4 


1-33  26-3 

1-28  28-4 

1  23  19-5 

1-19  16-2 

115  130 

111  9-5 

106  4-7 


POTASSIUM.  219 

Teroxide  op  potassium,  KO3. — This  is  an  orange-yellow  fusible  substance, 
generated  when  potassium  is  burned  in  excess  of  dry  oxygen  gas,  and  also 
formed,  to  a  small  extent,  when  hydrate  of  potassa  is  long  exposed,  in  a 
melted  state,  to  the  air.  When  nitre  is  decomposed  by  a  strong  heat,  per- 
oxide of  potassium  is  also  produced.  It  is  decomposed  by  water  into  potassa, 
which  unites  with  the  latter,  and  into  oxygen  gas. 

Carbonate  of  potassa,  KO,  C02-f-2HO.  —  Salts  of  potassa  containing  a 
vegetable  acid  are  of  constant  occurrence  in  plants,  where  they  perform  im- 
portant, but  not  yet  perfectly  understood,  functions  in  the  economy  of  those 
beings.  The  potassa  is  derived  from  the  soil,  which,  when  capable  of  sup- 
porting vegetable  life,  always  contains  that  substance.  When  plants  are 
burned,  the  organic  acids  are  destroyed,  and  the  potassa  left  in  the  state  of 
carbonate. 

It  is  by  these  indirect  means  that  carbonate,  and,  in  fact,  nearly  all  the 
salts  of  potassa,  are  obtained ;  the  great  natural  depository  of  the  alkali  is 
the  felspar  of  granitic  and  other  unstratified  rocks,  where  it  is  combined 
with  silica,  and  in  an  insoluble  state.  Its  extraction  thence  is  attended  with 
too  many  difficulties  to  be  attempted  on  the  large  scale ;  but  when  these 
rocks  disintegrate  into  soils,  and  the  alkali  acquires  solubility,  it  is  gradually 
taken  up  by  plants,  and  accumulates  in  their  substance  in  a  condition  highly 
favourable  to  its  subsequent  applications. 

Potassa-salts  are  always  most  abundant  in  the  green  and  tender  parts  of 
plants,  as  may  be  expected,  since  from  these  evaporation  of  nearly  pure 
water  takes  place  to  a  large  extent ;  the  solid  timber  of  forest  trees  contains 
comparatively  little. 

In  preparing  the  salt  on  an  extensive  scale,  the  ashes  are  subjected  to  a 
process  called  lixiviation ;  they  are  put  into  a  large  cask  or  tun,  having  an 
aperture  near  the  bottom,  stopped  by  a  plug,  and  a  quantity  of  water  is 
added.  After  some  hours  the  liquid  is  drawn  off,  and  more  water  added, 
that  the  whole  of  the  soluble  matter  may  be  removed.  The  weakest  solutions 
are  poured  upon  fresh  quantities  of  ash,  in  place  of  water.  The  solutions 
are  then  evaporated  to  dryness,  and  the  residue  calcined,  to  remove  a  little 
brown  organic  matter ;  the  product  is  the  crude  potash  or  pearlash  of  com- 
merce, of  which  very  large  quantities  are  obtained  from  Russia  and  America. 

This  salt  is  very  impure ;  it  contains  silicate  and  sulphate  of  potassa, 
chloride  of  potassium,  &c. 

The  purified  carbonate  of  potassa  of  pharmacy  is  prepared  from  the  crude 
article,  by  adding  an  equal  weight  of  cold  water,  agitating,  and  filtering; 
most  of  the  foreign  salts  are,  from  their  inferior  degree  of  solubility,  left 
behind.  The  solution  is  then  boiled  down  to  a  very  small  bulk,  and  suffered 
to  cool,  when  the  carbonate  separates  in  small  crystals  containing  2  equiv. 
of  water,  which  are  drained  from  the  mother-liquor,  and  then  dried  in  a  stove. 

A  still  purer  salt  may  be  obtained  by  exposing  to  a  red-heat  purified 
cream  of  tartar  (acid  tartrate  of  potassa),  and  separating  the  carbonate  by 
solution  in  water  and  crystallization,  or  evaporation  to  dryness. 

Carbonate  of  potassa  is  extremely  deliquescent,  and  soluble  in  less  than 
its  own  weight  of  water;  the  solution  is  highly  alkaline  to  test-paper.  It  is 
insoluble  in  alcohol.  By  heat  the  water  of  crystallization  is  driven  off,  and 
by  a  temperature  of  full  ignition  the  salt  is  fused,  but  not  otherwise  changed 
This  substance  is  largely  used  in  the  arts,  and  is  a  compound  of  great  im- 
portance. 

Bicarbonate  of  potassa,  KO,  COj-fHO,  CO,.  —  When  a  stream  of  car- 
bonic acid  gas  is  passed  through  a  cold  solution  of  carbonate  of  potassa,  the 
gas  is  rapidly  absorbed,  and  a  white,  crystalline,  and  less  soluble  substance 
separated,  which  is  the  new  compound.  It  is  collected,  pressed,  le-dissolved 
in  warm  water,  and  the  solution  left  to  crystallize. 


220  POTASSIUM. 

Bicarbonate  of  potassa  is  much  le^s  soluble  than  simple  carbonate ;  it  re- 
quires for  that  purpose  4  parts  of  cold  water.  The  solution  is  nearly  neutral 
to  test-paper,  and  has  a  much  milder  taste  than  the  preceding  salt.  When 
boiled,  carbonic  acid  is  disengaged.  The  crystals,  which  are  large  and  beau- 
tiful, derive  their  form  from  a  right  rhombic  prism ;  they  are  decomposed 
by  heat,  water  and  carbonic  acid  being  extricated,  and  simple  carbonate  left 
behind. 

Nitrate  of  potassa  ;  nitre  ;  saltpetre,  KO,  NOg.  —  This  important 
compound  is  a  natural  product,  being  disengaged  by  a  kind  of  efflorescence 
from  the  surface  of  the  soil  in  certain  dry  and  hot  countries.  It  may  also  be 
produced  by  artificial  means,  namely,  by  the  oxidation  of  ammonia  in  pres- 
ence of  a  powerful  base. 

In  France,  large  quantities  of  artificial  nitre  are  prepared  by  mixing  animal 
refuse  of  all  kinds  with  o'  "♦  mortar  or  hydrate  of  lime  and  earth,  and  placing 
the  mixture  in  heaps,  pr/»*cted  from  the  rain  by  a  roof,  but  freely  exposed 
to  the  air.  From  time  to  time  the  heaps  are  watered  with  putrid  urine,  and 
the  mass  turned  over,  to  expose  fresh  surfaces  to  the  air.  When  much  salt 
has  been  formed,  the  mixture  is  lixiviated,  and  the  solution,  which  contains 
nitrate  of  lime,  mixed  with  carbonate  of  potassa ;  carbonate  of  lime  is  formed, 
and  the  nitric  acid  transferred  to  the  alkali.  The  filtered  solution  is  then 
made  to  crystallize,  and  the  crystals  purified  by  re-solution  and  crystalliza- 
tion several  times  repeated.  , 

All  the  niti'e  used  in  this  country  comes  from  the  East  Indies ;  it  is  dis- 
solved in  water,  a  little  carbonate  of  potassa  added  to  precipitate  lime,  and 
then  the  salt  purified  as  above. 

Nitrate  of  potassa  crystallizes  in  anhydrous  six-sided  prisms,  with  dihedral 
summits;  it  is  soluble  in  7  parts  of  water  at  60°  (15°-5C),  and  in  its  own 
weight  of  boiling  water.  Its  taste  is  saline  and  cooling,  and  it  is  without 
action  on  vegetable  colours.  At  a  temperature  below  redness  it  melts,  and 
by  a  strong  heat  is  completely  decomposed. 

When  thrown  on  the  surface  of  many  metals  in  a  state  of  fusion,  or  when 
mixed  with  combustible  matter  and  heated,  rapid  oxidation  ensues,  at  the 
expense  of  the  oxygen  of  the  nitric  acid.  Examples  of  such  mixtures  are 
found  in  common  gunpowder,  and  in  nearly  all  pyrotechnic  compositions, 
which  burn  in  this  manner  independently  of  the  oxygen  of  the  air,  and  even 
under  water.  Gunpowder  is  made  by  very  intimately  mixing  together  nitrate 
of  potassa,  charcoal,  and  sulphur,  in  proportions  which  approach  1  eq.  nitre, 
3  eq.  carbon,  and  1  eq.  sulphur. 

These  quantities  give,  reckoned  to  100  parts,  and  compared  with  the  pro- 
portions used  in  the  manufacture  of  the  English  government  powder,'  the 
following  results : — 

Theory.    Proportions  in  practioe. 

Nitrate  of  potassa 74-8  75 

Charcoal 13-3  15 

Sulphur  11-9  10 

100-  100 

The  nitre  is  rendered  very  pure  by  the  means  already  mentioned,  freed 
from  water  by  fusion,  and  ground  to  fine  powder :  the  sulphur  and  charcoal, 
the  latter  being  made  from  light  wood,  as  dogwood  or  elder,  are  also  finely 
groimd,  after  which  the  materials  are  weighed  out,  moistened  with  water, 
and  thoroughly  mixed,  by  grinding  under  an  edge-mill.  The  mass  is  then 
subjected  to  great  pressure,  and  the  mill-cake  thus  produced  broken  in  pieces, 

*  Dr.  M'CuUoeh,  Ency.  Brit. 


POTASSIUM.  221 

and  placed  in  sieves  made  of  perforated  vellum,  moved  by  macHiuery,  each 
containing,  in  addition,  a  round  piece  of  heavy  wood.  The  grains  of  powder 
broken  oflf  by  attrition  fall  through  the  holes  in  the  skin,  and  are  easily  sepa- 
rated from  the  dust  by  sifting.  The  powder  is,  lastly,  dried  by  exposure  to 
steam-heat,  and  sometimes  glazed  or  polished  by  agitation  in  a  kind  of  cask 
mounted  on  an  axis. 

When  gunpowder  is  fired,  the  oxygen  of  the  nitrate  of  potassa  is  trans 
ferred  to  the  carbon,  forming  carbonic  acid ;  the  sulphur  combines  with  the 
potassium,  and  the  nitrogen  is  set  free.     The  large  volume  of  gas  thus  pro- 
duced, and  still  farther  expanded  by  the  very  exalted  temperature,  suffi- 
ciently accounts  for  the  explosive  effects. 

Sulphate  of  potassa,  K0,S03. —  The  acid  residue  left  in  the  retort  when 
nitric  acid  is  prepared  is  dissolved  in  water,  and  neutralized  with  crude  car- 
bonate of  potassa.  The  solution  furnishes,  on  cooling,  hard  transparent 
crystals  of  the  neutral  sulphate,  which  may  be  re-dissolved  in  boiling  water, 
and  re-crystallized. 

Sulphate  of  potassa  is  soluble  in  about  10  parts  of  cold,  and  in  a  much 
smaller  quantity  of  boiling  water  ;  it  has  a  bitter  taste,  and  is  neutral  to 
test-paper.  The  crystals  much  resemble  those  of  quartz  in  figure  and  ap 
pearance ;  they  are  anhydrous,  and  decrepitate  when  suddenly  heated, 
which  is  often  the  case  with  salts  containing  no  water  of  crystallization. 
They  are  quite  insoluble  in  alcohol. 

BisuLPHATE  OF  POTASSA,  KO.SOg  -|-  H0,S03.  The  neutral  sulphate  iu 
powder  is  mixed  with  half  its  weight  of  oil  of  vitriol,  and  the  whole  evapo- 
rated quite  to  dryness  in  a  platinum  vessel,  placed  under  a  chimney ;  tlie 
fused  salt  is  dissolved  in  hot  water,  and  left  to  crystallize.  The  crystals 
have  the  figure  of  flattened  rhombic  prisms,  and  are  much  more  soluble  than 
the  neutral  salt,  requiring  only  twice  their  weight  of  water  at  G0°  (lo°-5C), 
and  less  than  half  that  quantity  at  212°  (100°C).  The  solution  has  a  sour 
taste  and  strong  acid  reaction. 

BisuLPHATE  OF  POTASSA,  ANHYDROUS,  KO,2S03. — Equal  weights  of  neutral 
sulphate  of  potassa  and  oil  of  vitriol  are  dissolved  in  a  small  quantity  of 
warm  distilled  water,  and  set  aside  to  cool.  The  anhydrous  sulphate  crys- 
tallizes out  in  long  delicate  needles,  which  if  left  several  days  in  the  mother- 
liquor  disappear,  and  give  place  to  crystals  of  the  ordinary  hydrated  bisul- 
phate  above  described.  This  salt  is  decomposed  by  a  large  quantity  of 
water.' 

Sesquisulphate  OF  POTASSA,  2(KO,S03)  -j-  H0,S03. — A  salt,  crytallizing 
in  fine  needles  resembling  those  of  asbestos,  and  having  the  composition 
stated,  was  obtained  by  Mr.  Phillips  from  the  nitric  acid  residue.  M.  Jacque- 
lain  was  unsuccessful  in  his  attempts  to  reproduce  this  compound. 

Chlorate  of  potassa,  KOjClOg. — The  theory  of  the  production  of  chloric 
acid,  by  the  action  of  chlorine  gas  on  a  solution  of  caustic  potassa,  has  been 
already  described  (p.  145). 

Chlorine  gas  is  conducted  by  a  wide  tube  into  a  strong  and  warm  solution 
of  carbonate  of  potassa,  until  absorption  of  the  gas  ceases.  The  liquid  is, 
if  necessary,  evaporated,  and  then  allowed  to  cool,  in  order  that  the  slightly 
soluble  chlorate  may  crystallize  out.  The  mother-liquid  affords  a  second 
crop  of  crystals,  but  they  are  much  more  contaminated  by  chloride  of  potas- 
Bium,     It  may  be  purified  by  one  or  two  re-crystallizations. 

Chlorate  of  potassa  is  soluble  in  about  20  parts  of  cold,  and  2  of  boiling 
water ;  the  crystals  are  anhydrous,  flat,  and  tabular ;  in  taste  it  somewhai 
resembles  nitre.  Heated,  it  disengages  oxygen  gas  from  both  acid  and  base, 
and  leaves  chloride  of  potassium.     By  arresting  the  decomposition  when  the 

*  Jacquelain,  Ann.  China,  et  Phys.  vol.  vii.  p.  31^ 
19*  ^  ^ 


222  POTASSIUM. 

evolution  of  gas  begins,  and  re-dissolving  the  salt,  perchlorate  of  potassa 
and  chloride  of  potassium  may  be  obtained. 

This  salt  deflagrates  violently  with  combustible  matter,  explosion  often 
occurring  by  friction  or  blows.  When  about  one  grain  weight  of  chlorate 
and  an  equal  quantity  of  sulphur  are  rubbed  in  a  mortar,  the  mixture  ex- 
plodes with  a  loud  report ;  hence  it  cannot  be  used  in  the  preparation  of  gun- 
powder instead  of  nitrate  of  potassa.  Chlorate  of  potassa  is  now  a  large 
article  of  commerce,  being  employed,  together  with  phosphorus,  in  making 
instantaneous  light  matches. 

Peechlorate  of  potassa,  KO.CIO,.  —  This  has  been  already  noticed 
under  the  head  of  perchloric  acid.  It  is  best  prepared  by  projecting 
powdered  chlorate  of  potassa  into  warm  nitric  acid,  when  the  chloric  acid  is 
resolved  into  perchloric  acid,  chlorine,  and  oxygen  gases.  The  salt  is 
separated  by  crystallization  from  the  nitrate.  Perchlorate  of  potassa  is  a 
very  feebly  soluble  salt ;  it  requires  55  parts  of  cold  water,  but  is  more  freely 
taken  up  at  a  boiling  heat.  The  crystals  are  small,  and  have  the  figure  of 
an  octahedron,  with  square  base.  It  is  decomposed  by  heat,  in  the  same 
manner  as  chlorate  of  potassa. 

Sulphides  of  potassium.  —  There  are  not  less  than  five  or  six  distinct 
compounds  of  potassium  and  sulphur,  of  which,  however,  only  three  are  of 
sufficient  importance  to  be  noticed  here ;  these  are  the  compounds,  contain- 
ing KS,  KS3,  and  KSg. 

Simple  ov  proiosulphide  of  potassium,  is  formed  by  directly  combining  the 
metal  with  sulphur,  or  by  reducing  sulphate  of  potassa  at  a  red-heat  by  hy- 
drogen or  charcoal  powder.  Another  method  is  to  take  a  strong  solution  of 
hydrate  of  potassa,  and  after  dividing  it  into  two  equal  portions,  saturate 
the  one  with  sulphuretted  hydrogen  gas,  and  then  add  the  remainder.  The 
whole  is  then  evaporated  to  dryness  in  a  retort,  and  the  residue  fused. 

The  protosulphide  is  a  crystalline  cinnabar-red  mass,  very  soluble  in  water. 
The  solution  has  an  exceedingly  ofi'ensive  and  caustic  taste,  and  is  decom- 
posed by  acids,  even  carbonic  acid,  with  evolution  of  sulphuretted  hydrogen, 
and  formation  of  a  salt  of  the  acid  used.  This  compound  is  a  strong  sulphur- 
base,  and  unites  with  the  sulphides  of  hydrogen,  carbon,  arsenic,  &c.,  forming 
crystallizable  saline  compounds.  One  of  these,  KS-j-HS,  is  produced  when 
hydrate  of  potassa  is  saturated  with  sulphuretted  hydrogen,  as  before  men- 
tioned. 

The  higher  sulphides  are  obtained  by  fusing  the  protosulphide  with  dif- 
ferent proportions  of  sulphur.  They  are  soluble  in  water,  and  decomposed 
by  acids,  in  the  same  manner  as  the  foregoing  compound,  with  this  addition, 
that  the  excess  of  sulphur  is  precipitated  as  a  fine  white  powder. 

Hepar  sulphuris  is  a  name  given  to  a  brownish  substance,  sometimes  used 
in  medicine,  made  by  fusing  together  different  proportions  of  carbonate  of 
potassa  and  sulphur.  It  is  a  variable  mixture  of  the  two  higher  sulphides 
with  hyposulphite  and  sulphate  of  potassa. 

When  equal  parts  of  sulphur  and  dry  carbonate  of  potassa  are  melted  to- 
gether at  a  temperature  not  exceeding  482°  (250°C.),  the  decomposition  of 
the  salt  is  quite  complete,  and  all  the  carbonic  acid  is  expelled.  The  fused 
mass  dissolves  in  water,  with  the  exception  of  a  little  mechanically-mixed 
sulphur,  with  dark  brown  colour,  and  the  solution  is  found  to  contain  nothing 
besides  pentasulphide  of  potassium  and  hyposulphite  of  potassa. 

{2  eq.  potassium__ _^  2  eq.  of  pentasulphide  of  po- 
2  eq.  oxygen              ^^^'^^'^       sium. 
1  eq.  potassa ]^[^^]^><;;[^ 

12  eq.  sulphur  {1^  ^^;  ^IJIpJ^J"^!:^^^.  1  ,q.  hyposulphite  of  po- 

tassa. 


POTASSIUM.  223 

When  the  mixture  has  been  exposed  to  a  temperature  approaching  that 
of  ignition,  it  is  found  on  the  contrary  to  contain  sulphate  of  potassa,  arising 
from  the  decomposition  of  the  hyposulphite  which  then  occurs. 

4  eq  r  1  eq-  potassium 1  eq.  pentasulphide 

4eq.hyposul-    potassa     j    3  e?' tasTaV    ^-^"""^         of  potassium. 
phiteofpo-4,         ,       I  deq.potassa^    ^ 
tassa.  1  ^  ®^-  ^y-  f   ^  ®^'  sulphur- 

*^^^*  posulph.  \    3  eq.  sulphur, 

acid  (.  8  eq.  oxygen =^^^^  3   eq.   sulphate  of 

potassa. 

From  both  these  mixtures  the  pentasulphide  of  potassium  may  be  ex- 
tracted by  alcohol,  in  which  it  dissolves. 

When  tho-carbonate  ig  fused  with  half  its  weight  of  sulphur  only,  then  the 
tersulphide,^KS3,  is  produced  instead  of  that  above  indicated ;  3  eq.  of  po- 
tassa and  8  eq.  of  sulphur  containing  the  elements  of  2  eq.  sulphide  and  1 
eq.  hyposulphite. 

The  effects  described  happen  in  the  same  manner  when  hydrate  of  potassa 
is  substituted  for  the  carbonate  ;  and  also,  when  a  solution  of  the  hydrate  is 
boiled  with  sulphur,  a  mixture  of  sulphide  and  hyposulphite  always  results. 

Chloride  of  potassium,  KCl.  —  This  salt  is  obtained  in  large  quantity  in 
the  manufacture  of  chlorate  of  potassa ;  it  is  easily  purified  from  any  portions 
of  the  latter  by  exposure  to  a  dull  red-heat.  It  is  also  contained  in  kelp, 
and  is  separated  for  the  use  of  the  alum-maker. 

Chloride  of  potassium  closely  resembles  common  salt  in  appearance,  as- 
suming, like  that  substance,  the  cubic  form  of  crystallization.  The  crystals 
dissolve  in  three  parts  of  cold,  and  in  a  much  less  quantity  of  boiling  water; 
they  are  anhydrous,  have  a  simple  saline  taste,  with  slight  bitterness,  and 
fuse  when  exposed  to  a  red-heat.  Chloride  of  potassium  is  volatilized  by  a 
very  high  temperature.  ^ 

Iodide  of  potassium,  KI.  —  "Kere  are  two  different  methods  of  preparing 
this  important  medicinal  compound. 

(1.)  When  iodine  is  added  to  a  strong  solution  of  caustic  potassa  free  from 
carbonate,  it  is  dissolved  in  large  quantity,  forming  a  colourless  solution' 
containing  iodide  of  potassivim  and  iodate  of  potassa;  the  reaction  is  the 
same  as  in  the  analogous  case  with  chlorine.  When  the  solution  begins  to 
be  permanently  coloured  by  the  iodine,  it  is  evaporated  to  dryness,  and  cau- 
tiously heated  red-hot,  by  which  the  iodate  of  potassa  is  entirely  converted 
into  iodide  of  potassium.  The  mass  is  then  dissolved  in  water,  and  after  fil- 
tration, made  to  crystallize. 

(2.)  Iodine,  water,  and  iron-filings  or  scraps  of  zinc,  are  placed  in  a  warm 
situation  until  the  combination  is  complete,  and  the  solution  colourless.  The 
resulting  iodide  of  iron  or  zinc  is  then  filtered,  and  exactly  decomposed  with 
solution  of  pure  carbonate  of  potassa,  great  care  being  taken  to  avoid  excess 
of  the  latter.  Iodide  of  potassium  and  carbonate  of  protoxide  of  iron,  or 
zinc,  are  obtained ;  the  former  is  separated  by  filtration,  and  evaporated 
until  the  solution  is  sufficiently  concentrated  to  crystallize  on  cooling,  the 
washings  of  the  filter  being  added  to  avoid  loss. 

Iodide  of  iron /  1°^^^® ^^  ^^^^^^  °^  potassium. 

\  Iron — V. 

}                (■  Potassium  • 
Potassa  I  Oxygen  -~^__\^ 
Carbonic  acid "^  Carbonate  of  protoxide 

of  iron. 
The  second  method  is,  on  the  whole,  to  be  preferred. 


224  SODIUM. 

Iodide  of  potassium  crystallizes  in  cubes,  which  are  often,  from  some  un- 
explained cause,  milk-white  and  opaque ;  they  are  anhydrous,  and  fuse 
readily  when  heated.  The  ealt  is  very  soluble  in  water,  but  not  deliquescent, 
when  pure,  in  a  moderately  dry  atmosphere  ;  it  is  dissolved  by  alcohol. 

Solution  of  iodide  of  potassium,  like  those  of  all  the  soluble  iodides,  dis- 
Bolves  a  large  quantity  of  free  iodine,  forming  a  deep  brown  liquid,  not  de- 
composed by  water. 

Bromide  of  potassium,  KBr. — This  compound  may  be  obtained  by  pro- 
cesses exactly  similar  to  those  just  described,  substituting  bromine  for  the 
iodine.  It  is  a  colourless  and  very  soluble  salt,  quite  indistinguishable  in 
appearance  and  geujral  characters  from  the  iodide. 


The  salts  of  potassa  are  colourless,  when  not  associated  with  a  coloured 
metallic  oxide  or  acid.  They  are  all  more  or  less  soluble  in  waiter,  and  may 
be  distinguished  by  the  following  characters : — 

(1.)  Solution  of  tartaric  acid  added  to  a  moderately  strong  solution  of  a 
potassa-salt,  gives,  after  some  time,  a  white,  crystalline  precipitate  of  cream 
of  tartar ;  the  effect  is  greatly  promoted  by  strong  agitation. 

(2.)  Solution  of  bichloride  of  platinum,  with  a  little  hydrochloric  acid,  if 
necessary,  gives,  under  similar  circumstances,  a  crystalline  yellow  precipi- 
tate, which  is  a  double  salt  of  bichloride  of  platinum  and  chloride  of  potas- 
sium. Both  this  compound  and  cream  of  tartar  are,  however,  soluble  in 
about  60  parts  of  cold  water.  An  addition  of  alcohol  increases  the  delicacy 
of  both  tests. 

(3.)  Perchloric  acid,  and  hydrofluosilicic  acid,  give  rise  to  slightly-soluble 
white  precipitates  when  added  to  a  potassa-salt. 

(4.)  Salts  of  potassa  usually  colour  the  outer  blowpipe  flame  purple  or 
violet ;  this  reaction  is  clearly  perceptible  only  when  the  potassa-salts  are 
pure. 

SODIUM^ 

This  metal  was  obtained  by  Davy  very  shortly  after  the  discovery  of  po- 
tassium, and  by  similar  means.  It  may  be  prepared  in  large  quantity  by 
decomposing  carbonate  of  soda  by  charcoal  at  a  high  temperature. 

Six  parts  of  anhydrous  carbonate  of  soda  are  dissolved  in  a  little  hot 
water,  and  mixed  with  two  parts  of  finely-powdered  charcoal  and  one  part 
of  charcoal  in  lumps.  The  whole  is  then  evaporated  to  dryness,  transferred 
to  the  iron  retort  before  described,  and  heated  in  the  same  manner  to  white- 
ness. A  receiver  containing  rock-oil  is  adapted  to  the  tube,  and  the  whole 
operation  carried  on  in  the  same  way  as  when  potassium  is  made.  The  pro- 
cess, when  well  conducted,  is  easier  and  more  certain  than  that  of  making 
potassium. 

Sodium  is  a  silver-white  metal,  greatly  resembling  potassium  in  every  re- 
spect; it  is  soft  at  common  temperatures,  melts  at  194°  (90°C),  and  oxidizes 
very  rapidly  in  the  air.  Its  specific  gravity  is  0-972.  Placed  upon  the  sur- 
face of  cold  water,  sodium  decomposes  that  liquid  with  great  violence,  but 
seldom  takes  fire  unless  the  motions  of  the  fragment  be  restrained,  and  its 
rapid  cooling  diminished,  by  adding  gum  or  starch  to  the  water.  With  hot 
water  it  takes  fire  at  once,  burning  with  a  bright  yellow  flame,  and  giving 
rise  to  a  solution  of  soda. 

The  equivalent  of  sodium  is  23,  and  its  symbol  (Natrium)  Na. 

There  are  two  well-defined  compounds  of  sodium  and  oxygen ;  the  pro- 
toxide, anhydrous  soda,  NaO,  and  the  binoxide,  NaOg,  or  perhaps,  teroxide 
NaOg ;  they  are  formed  by  burning  sodium  in  air  or  oxygen  gas,  and  resem- 
ble in  every  respect  the  corresponding  compounds  of  potassium. 

Hydrate  of  soda,  NaO,  HO. — This  substance  is  prepared  in  practice  by 


SODIUM. 


225 


decomposing  a  somewhat  dilute  solution  of  carbonate  of  soda  by  hydrate  of 
lime ;  the  description  of  the  process  employed  in  the  case  of  hydrate  of  po- 
tassa,  and  the  precautions  necessary,  apply  word  for  word  to  that  of  soda. 

The  splid  hydrate  is  a  white,  fusible  substance,  very  similar  in  properties 
to  hydrate  of  potassa.  It  is  deliquescent,  but  dries  up  again  after  a  time  in 
consequence  of  the  absorption  of  carbonic  acid.  The  solution  is  highly  al- 
kaline, and  a  powerful  solvent  for  animal  matter;  it  is  used  in  large  quan- 
tity for  making  soap. 

The  strength  of  a  solution  of  caustic  soda  may  be  roughly  determined 
from  a  knowledge  of  its  density,  by  the  aid  of  the  following  table  drawn  up 
by  Dr.  Dalton. 


TABLE    OP   DENSITY. 


Density. 

2-00 
1-85 
1-72 
1-63 
1-55 
1-50 
1-47 
1-44 


Percentage  of 
real  soda. 


77-8 

1-40 

63-6 

1-36 

53-8 

1-32 

46-6 

1-29 

41-2 

1-23 

36-8 

M8 

34-0 

1-12 

31-0 

106 

Density. 


Percentage  of 
real  s<xla. 


29-0 
260 
23-0 
190 
16-0 
130 
9-0 
4-7 


Carbonate  of  soda,  NaOjCOj-f  lOHO. — Carbonate  of  soda  was  once  ex 
clusively  obtained  from  the  ashes  of  sea-weeds,  and  of  plants,  such  as  the 
Salsola  soda,  which  grew  by  the  sea-side,  or,  being  cultivated  in  suitable  lo- 
calities for  the  purpose,  were  afterwards  subjected  to  incineration.  The 
barilla,  yet  employed  to  a  small  extent  in  soap-making,  is  thus  produced  in 
several  places  on  the  coast  of  Spain,  as  Alicant,  Carthagena,  &c.  That 
made  in  Brittany  is  called  varec. 

Carbonate  of  soda  is  now  manufactured  on  a  stupendous  scale  from  com- 
mon salt,  or  rather  from  sulphate  of  soda,  by  a  process  of  which  the  follow- 
ing is  an  outline : — 

A  charge  of  6001b.  of  common  salt  Vis  placed  upon  the  hearth  of  a  well- 
heated  reverberatory  furnace,  and  an  equal  weight  of  sulphuric  acid  of  sp. 
gr.  1-6  poured  upon  it  through  an  opening  in  the  roof,  and  thoroughly  min- 
gled with  the  salt ;  hydrochloric  acid  gas  is  disengaged,  which  is  either 
allowed  to  escape  by  the  chimney,  or  condensed  by  suitable  apparatus,  and 
the  salt  is  converted  into  sulphate  of  soda.  This  part  of  the  process  takes 
for  completion  about  four  hours,  and  requires  much  care  and  skill. 

The  sulphate  is  next  reduced  to  powder,  and  mixed  with  an  equal  weight 
of  chalk  or  limestone,  and  half  as  much  small  coal,  both  ground  or  crushed. 
The  mixture  is  thrown  into  a  reverberatory  furnace,  and  heated  to  fusion, 
with  constant  stirring ;  2  cwt.  is  about  the  quantity  operated  on  at  once. 
When  the  decomposition  is  judged  complete,  the  melted  matter  is  raked  from 
the  surface  into  an  iron  trough,  where  it  is  allowed  to  cool.  When  cold,  it 
is  broken  up  into  little  pieces,  and  lixiviated  with  cold  or  tepid  water.  The 
solution  is  evaporated  to  dryness,  and  the  salt  calcined  with  a  little  saw-dust 
in  a  suitable  furnace.  The  product  is  the  soda-ash,  or  British  alkali  of  com- 
merce, which,  when  of  good  quality,  contains  from  48  to  52  per  cent,  of 
pure  soda,  partly  in  the  state  of  carbonate,  and  partly  as  hydrate,  the  re 
mainder  being  chiefly  sulphate  of  soda  and  common  salt,  with  occasional 
traces  of  sulphite  or  hyposulphite,  and  also  cyanide  of  sodium.    By  dissolving 


*  Qraham,  Elements,  p. 


226  SODIUM. 

soda-ash  in  hot  water,  filtering  the  solution,  and  then  allowing  it  to  cool 
slowly,  the  carbonate  is  deposited  in  large  transparent  crystals. 

The  reaction  which  takes  place  in  the  calcination  of  the  sulphate  with 
chalk  and  coal-dust  seems  to  consist,  first,  in  the  conversion  of  the  sulphate 
of  soda  into  sulphide  of  sodium  by  the  aid  of  the  combustible  matter,  and, 
secondly,  in  the  double  interchange  of  elements  between  that  substance  and 
the  carbonate  of  lime. 


Sulphur Sulphide  of  calcium. 


Sulphide  of  sodium  {IXm 


f  T  *       /  CJalcium 
Carbonate  of  lime   -]     ^°^®  \  Oxygen 

(  Carbonic  acid --^=^w   Carbonate  of  soda. 

The  sulphide  of  calcium  combines  with  another  proportion  of  lime  to  form 
a  peculiar  compound,  which  is  insoluble  in  cold  or  slightly  warm  water. 

Other  processes  have  been  proposed,  and  even  carried  into  execution,  but 
the  above,  which  was  originally  proposed  by  M.  Leblanc,  is  found  most  ad- 
vantageous. 

The  ordinary  crystals  of  carbonate  of  soda  contain  ten  equivalents  of  water, 
but  by  particular  management  the  same  salt  may  be  had  with  fifteen,  nine, 
seven,  equivalents,  or  sometimes  with  only  one.  The  common  form  of  the 
crystal  is  derived  from  an  oblique  rhombic  prism ;  they  eflBoresce  in  dry  air, 
and  crumble  to  a  white  powder.  Heated,  they  fuse  in  their  water  of  crys- 
tallization ;  when  the  latter  has  been  expelled,  and  the  dry  salt  exposed  to 
a  full  red-heat,  it  melts  without  undergoing  change.  The  common  crystals 
dissolve  in  two  parts  of  cold,  and  in  less  than  their  own  weight  of  boiling 
water ;  the  solution  has  a  strong,  disagreeable,  alkaline  taste,  and  a  power- 
ful alkaline  reaction. 

Bicarbonate  of  soda,  NaO,C02 -}-  H0,C02.  —  This  salt  is  prepared  by 
passing  carbonic  acid  gas  into  a  cold  solution  of  the  neutral  carbonate,  or 
by  placing  the  crystals  in  an  atmosphere  of  the  gas,  which  is  rapidly  ab- 
sorbed, while  the  crystals  lose  the  greater  part  of  their  water,  and  pass  into 
the  new  compound. 

Bicarbonate  of  soda,  prepared  by  either  process,  is  a  crystalline  white 
powder,  which  cannot  he  re-dissolved  in  warm  water  without  partial  decom- 
position. It  requires  10  parts  of  water  at  60°  (15°-5C)  for  solution;  the 
liquid  is  feebly  alkaline  to  test-paper,  and  has  a  much  milder  taste  than  that 
of  the  simple  carbonate.  It  does  not  precipitate  a  solution  of  magnesia. 
By  exposure  to  heat,  the  salt  is  converted  into  neutral  carbonate. 

A  sesquicarbonate  of  soda  containing  2Na0,3C0j-j-4H0  has  been  described 
by  Mr,  Phillips ;  like  the  sesquicarbonate  of  potassa,  it  is  formed  at  plea- 
sure only  with  difficulty.  This  salt  occurs  native  on  the  banks  of  the  soda- 
lakes  of  Sokena  in  Africa,  whence  it  is  e?:ported  under  the  name  of  irona. 

Alkalimetry;  Analysis  of  Hydrates  and  Carbonates  of  the  Alkalis.  —  The 
general  principle  of  these  operations  consists  in  ascertaining  the  quantity 
of  real  alkali  in  a  given  weight  of  the  substance  examined,  by  finding  how 
much  of  the  latter  is  required  to  neutralize  a  known  quantity  of  an  acid,  as 
sulphuric  acia. 

The  first  step  is  the  preparation  of  a  stock  of  dilute  sulphuric  acid  of 
determinate  strength  ;  containing,  for  example,  100  grains  of  real  acid  in 
every  1,000  grain-measures  of  liquid  : '  a  large  quantity,  as  a  gallon  or  more, 

'  The  capacity  of  1,000  grains  of  distilled  water  at  60°  (15°5C).  The  p;rain-measure  of  water 
IB  often  found  a  very  convenient  and  useful  unit  of  volume  in  chemical  researches.  Vessels 
graduated  on  this  plan  bear  simple  comparison  with  the  imperial  gallon  and  pint,  and  fre- 
quently also  enable  tlie  operator  to  measure  out  a  liquid  of  known  density  instead  of  weigh- 
ing it. 


SODIUM.  227 

may  be  prepared  at  once  by  the  following  means.  The  oil  of  vitriol  is  first 
examined;  if  it  be  good  and  of  the  sp.  gr.  1-85  or  near  it,  the  process  is  ex- 
tremely simple ;  every  49  grains  of  the  liquid  acid  contains  40  grains  of 
absolute  acid ;  the  quantity  of  the  latter  required  in  the  gallon,  or  70,00fl 
grain-measures  of  dilute  acid,  will  be  of  course  7,000  grains.  This  is  eqtii 
valent  to  8.571  grains  of  the  oil  of  vitriol,  for 

Real  acid.        Oil  of  vitriol. 
40        :         49         =         7000        :         8575 

All  that  is  required  to  be  done,  therefore,  is  to  weigh  out  8,575  grains  of 
oil  of  vitriol,  and  dilute  it  with  so  much  water,  that  the  mixture,  when  cold, 
shall  measure  exactly  one  gallon. 

It  very  often  happens,  however,  that  the  oil  of  vitriol  to  be  used  is  not  so 
strong  as  that  above  mentioned ;  in  which  case  it  is  necessary  to  discover  ita 
real  strength,  as  estimated  from  its  saturating  power.  Pure  anhydrous  car- 
bonate of  soda  is  prepared  by  heating  to  dull  redness,  without  fusion,  the 
bicarbonate;  of  this  salt  53  grains,  or  1  eq.,  correspond  to  31  grains  of  soda, 
and  neutralize  40  grains  of  real  sulphuric  acid. 

A  convenient  quantity  is  carefully  weighed  out,  and  added,  little  by  little, 
to  a  known  weight,  say  100  grains,  of  the  oil  of  vitriol  to  be  tried,  diluted 
with  four  or  five  times  its  weight  of  water,  until  the  liquid,  after  warming, 
becomes  quite  neutral  to  test-paper.  By  weighing  again  the  residue  of  the 
carbonate,  it  is  at  once  known  how  much  of  the  latter  has  been  employed  ; 
the  amount  of  real  acid  in  the  hundi-ed  parts  of  the  oil  of  vitriol  is  then 
easily  calculated.  Thus,  suppose  the  quantity  of  carbonate  of  soda  used  to 
be  105  grains ;  then, 

Carb.  soda.  Sulph.  acid. 

63  :  40  =  105  :  79-24; 

79-24  grains  of  real  acid  are  consequently  contained  in  100  grains     Fig-  ^^^ 


of  oil  of  vitriol ;  consequently, 


-^^ 


9-24  :  100  =  7000  :  8833-82 


the  weight  in  grains  of  the  oil  of  vitriol  required  to  make  one 
gallon  of  the  dilute  acid. 

The  "  alkalimeter"  is  next  to  be  constructed.  This  is  merely  a 
1000-grain  measure,  made  of  a  piece  of  even,  cylindrical  glass  tube, 
about  15  inches  long  and  0-6  inch  internal  diameter,  closed  at  one 
extremity,  and  moulded  into  a  spout  or  lip  at  the  other.  Fig.  146. 
A  strip  of  ^aper  is  pasted  on  the  tube  and  sufi"ered  to  dry,  after 
which  the  instrument  is  graduated  by  counterpoising  it  in  a  nearly 
upright  position  in  the  pan  of  a  balance  of  moderate  delicacy,  and 
weighing  into  it,  in  succession,  100,  200,  300,  &c.,  grains  of  dis- 
tilled water  at  60°  (15° -50),  until  the  whole  quantity,  amounting 
to  1,000  grains,  has  been  introduced,  the  level  of  the  water  in  the 
tube  being,  after  each  addition,  carefully  marked  with  a  pen  upon 
the  strip  of  paper,  while  the  tube  is  held  quite  upright,  and  the 
mark  made  between  the  top  and  the  bottom  of  the  curve  formed  by 
the  surface  of  the  water.  The  smaller  divisions  of  the  scale,  of  10 
grains  each,  may  then  be  made  by  dividing  by  compasses  each  of 
the  spaces  into  ten  equal  parts.  When  the  graduation  is  complete, 
and  the  operator  is  satisfied  with  its  accuracy,  the  marks  may  be 
transferred  to  the  tube  itself  by  a  sharp  file,  and  the  paper  removed 
by  a  little  warm  water.  The  numbers  are  scratched  on  the  glass  with  the 
hard  end  of  the  same  file,  or  with  a  diamond.    When  this  alkalimeter  is  used 


2if  8  SODIUM. 

with  the  dilute  acid  described,  every  division  of  the  glass  will  correspond  to 
one  grain  of  real  sulphuric  acid. 

Let  it  be  required,  by  way  of  example,  to  test  the  commercial  value  of 
soda-ash,  or  to  examine  it  for  scientific  purposes :  50  grains  of  the  sample 
are  weighed  out,  dissolved  in  a  little  warm  water,  and,  if  necessary,  the 
solution  filtered ;  the  alkalimeter  is  then  filled  to  the  top  of  the  scale  with 
the  test-acid,  and  the  latter  poured  from  it  into  the  alkaline  solution,  which 
is  tried  from  time  to  time  with  red  litmus-paper.  The  addition  of  acid  must 
of  course  be  made  very  cautiously  as  neutralization  advances.  When  the 
solution,  after  being  heated  a  few  minutes,  no  longer  affects  either  blue  or 
red  test-paper,  the  measure  of  liquid  employed  is  read  off,  and  the  quantity 
of  soda  present  in  the  state  of  carbonate  or  hydrate  in  the  50  grains  of  salt 
found  by  the  rule  of  proportion.  Suppose  33  measures,  consequently  33 
grains  of  acid,  have  been  taken ;  then 
Sulph.  acid.  Soda. 

40         :         31         ==         33         :         25-57; 

the  sample  contains,  therefore,  51-2  per  cent,  of  available  alkali. 

It  will  be  easily  seen  that  the  principle  orthe  process  described  admits  of 
very  wide  application,  and  that,  by  the  aid  of  the  alkalimeter  and  carefully 
prepared  test-acid,  the  hydrates  and  carbonates  of  potassa,  soda,  and  am- 
monia, both  in  the  solid  state  and  in  solution,  can  be  examined  with  great 
ease  aud  accuracy.  The  quantity  of  real  alkali  in  a  solution  of  caustic  am- 
monia may  thus  be  determined,  the  equivalent  of  that  substance,  and  the 
amount  of  acid  required  to  neutralize  a  known  weight,  being  inserted  as  the 
second  and  third  terms  in  the  above  rule-of-three  statement.  The  same  acid 
answers  for  all. 

It  is  often  desirable,  in  the  analysis  of  carbonates,  to  determine  directly 
the  proportion  of  carbonic  acid ;  the  following  methods  leave  nothing  to  be 
desired  in  point  of  precision  :  — 

A  small  light  glass  flask  (fig.  147)  of  three   or  four 
Fig.  147.  ounces  capacity,  with  lipped  edge,  is  chosen,  and  a  cork 

fitted  to  it.  A  piece  of  tube  about  three  inches  long  is 
drawn  out  at  one  extremity,  and  fitted  by  means  of  a 
small  cork  and  a  bit  of  bent  tube,  to  the  cork  of  the 
flask.  This  tube  is  filled  with  fragments  of  chloride  of 
calcium,  prevented  from  escaping  by  a  little  cotton  at 
either  end ;  the  joints  are  secured  by  sealing-wax.  A 
short  tube,  closed  at  one  extremity,  and  small  enough  to 
go  into  the  flask,  is  also  provided,  and  the  apparatus  is 
complete.  Fifty  grains  of  the  carbonate  to  jg^  examined 
are  carefully  weighed  out  and  introduced  into  the  flask, 
together  with  a  little  water,  the  small  tube  is  then  filled  with  oil  of  vitriol, 
and  placed  in  the  flask  in  a  nearly  upright  position,  and  leaning  against  its 
side  in  such  a  manner  that  the  acid  does  not  escape.  The  cork  and  chloride 
of  calcium  tube  are  then  adjusted,  and  the  whole  apparatus  accurately 
counterpoised  on  the  balance.  This  done,  the  flask  is  slightly  inclined,  so 
that  the  oil  of  vitriol  may  slowly  mix  with  the  other  substances  and 
decompose  the  carbonate,  the  gas  from  which  escapes  in  a  dry  state  from 
the  extremity  of  the  tube.  When  the  action  has  entirely  ceased  the  liquid 
is  heated  until  it  boils,  and  the  steam  begins  to  condense  in  the  drying- tube ; 
it  is  then  left  to  cool,  and  weighed,  when  the  loss  indicates  the  quantity  of 
carbonic  acid.  The  acid  must  be  in  excess  after  the  experiment.  When 
carbonate  of  lime  is  thus  analyzed,  strong  hydrochloric  acid  must  be  substi- 
tuted for  the  oil  of  vitriol. 
Instead  of  the  above  apparatus,  a  neat  arrangement  may  be  used  which 


SODIUM 


229 


Fig.  148. 


■was  first  suggested  by  Will  and  Fresenius.  It  consists  of  two  snaall  glass 
flasks,  A  and  B,  fig.  148,  the  latter  being  somewhat  smaller  than  the  former. 
Both  the  flasks  are  provided  with  a  doubly  perforated  cork.  A  tube,  open  at 
both  ends,  but  closed  at  the  upper  extremity  by  means  of  a  small  quantity  of 
wax,  passes  through  the  cork  of  A,  to  the  very 
bottom  of  the  flask,  whilst  a  second  tube  reach- 
ing to  the  bottom  of  B,  establishes  a  communi- 
cation between  the  two  flasks.  The  cork  of  B 
is  provided,  moreover,  with  a  short  tube,  d.  In 
order  to  analyse  a  carbonate,  a  suitable  quan- 
tity (fifty  grains)  is  put  into  A,  together  with 
some  water.  B  is  half  filled  with  concentrated 
sulphuric  acid,  the  apparatus  tightly  fitted  and 
weighed.  A  small  quantity  of  air  is  now 
sucked  out  of  flask  B  by  means  of  the  tube  d, 
whereby  the  air  in  A  is  likewise  rarified.  Im- 
mediately a  portion  of  sulphuric  acid  ascends 
in  the  tube  c,  and  flows  over  into  flask  A, 
causing  a  disengagement  of  carbonic  acid, 
which  escapes  at  d,  after  having  been  perfectly 
dried  by  passing  through  the  bottle  B.     This 

operation  is  repeated  until  the  whole  of  the  carbonate  is  decomposed,  and 
the  process  terminated  by  opening  the  wax  stopper  and  drawing  a  quantity 
of  air  thi'ough  the  apparatus.  The  apparatus  is  now  re-weighed.  The  dif- 
ference of  the  two  weighings  expresses  the  quantity  of  carbonic  acid  in  the 
compound  analysed.' 

Sulphate  of^oda,  Glauber's  salts,  NaO,  SO3  -|-10HO.  —  This  is  a  by- 
product in  several  chemical  operations ;  it  may  of  course  be  prepar<id 
directly,  if  wanted  pure,  by  adding  dilute  sulphuric  acid  to  saturation  to  a 
solution  of  carbonate  of  soda.  It  crystallizes  in  a  figure  derived  from  au 
oblique  rhombic  prism ;  the  crystals  contain  10  eq.  of  water,  are  efflores- 
cent, and  undergo  watery  fusion  when  heated,  like  those  of  the  carbonate , 
they  are  soluble  in  twice  their  weight  of  cold  water,  and  rapidly  increase  in 
solubility  as  the  temperature  of  the  liquid  rises  to  91° -5  (33°C),  when  a 
maximum  is  reached,  100  parts  of  water  dissolving  322  parts  of  the  salt. 
Heated  beyond  this  point,  the  solubility  diminishes,  and  a  portion  of  sul- 
phate is  deposited.  A  warm  saturated  solution,  evaporated  at  a  high  tempe- 
rature, deposits  opaque  prismatic  crystals,  which  are  anhydrous.  This  salt 
has  a  slightly  bitter  taste,  and  is  purgative.  Mineral  springs  sometimes  con- 
tain it,  as  at  Cheltenham. 

BisuLPHATE  OF  SODA,  NaO,S03  -}-  H0,S03  -f-  3H0. — This  is  prepared  by 
adding  to  10  parts  of  anhydrous  neutral  sulphate,  7  of  oil  of  viMol,  evapo- 
rating the  whole  to  dryness,  and  gently  igniting.  The  bisulphate  is  very 
soluble  in  water,  and  has  an  acid  reaction.  It  is  not  deliquescent.  When 
very  strongly  heated,  the  fused  salt  gives  up  anhydrous  sulphuric  acid,  and 
becomes  simple  sulphate ;  a  change  which  necessarily  supposes  the  previous 
formation  of  a  true  anhydrous  bisulphate,  NaO,2S03. 

Hyposulphite  of  soda,  NaO,  S2OJ.  —  There  are  several  modes  of  procu^ 
ring  this  salt,  which  is  now  used  in  considerable  quantity  for  photographic 
purposes.  One  of  the  best  is  to  form  neutral  sulphite  of  soda,  by  passing  a 
stream  of  well  washed  sulphurous  acid  gas  into  a  strong  solution  of  carbo- 
nate of  soda,  and  then  to  digest  the  solution  with  sulphur  at  a  gentle  heat 
during  several  days.  By  careful  evaporation  at  a  modern  temperature,  the 
salt  is  obtained  in  large  and  regular  crystals,  which  are  very  soluble  in  water. 

'  A  convenient  modification  of  this  has  been  made  by  Dr.  Wetherill,    (Joum.  Frank.  Inst); 
and  another  by  Schaflncr.    (Chem.  Gazette,  Jan.  15, 1853.— R.  B.) 
20 


230  SODIUM. 

Nitrate  of  soda  ;  cubic  nitre,  NaO,  NO5. — Nitrate  of  soda  occurs  native, 
and  in  enormous  quantity,  at  Atacania,  in  Peru,  -where  it  forms  a  regular 
bed,  of  great  extent,  covered  with  clay  and  alluvial  matter.  The  pure  salt 
commonly  crystallizes  in  rhombohedrons,  resembling  those  of  calcareous 
spar,  but  is  probably  dimorphous.  It  is  deliquescent,  and  very  soluble  in 
water.  Nitrate  of  soda  is  employed  for  making  nitric  acid,  but  cannot  be 
used  for  gunpowder,  as  the  mixture  burns  too  slowly,  and  becomes  damp  in 
the  air.  It  has  been  lately  used  with  some  success  in  agriculture  as  a  su- 
perficial manure  or  top-dressing. 

Phosphates  of  soda;  common  tribasic  phosphate,  2NaO,  HO,  P05-f-24 
HO. — This  beautiful  salt  is  prepared  by  precipitating  the  acid  phosphate  of 
lime  obtained  by  decomposing  bone-earth  by  sulphuric  acid,  with  a  slight 
excess  of  carbonate  of  soda.  It  crystallizes  in  oblique  rhombic  prisms, 
which  are  efflorescent.  The  crystals  dissolve  in  4  parts  of  cold  water,  and 
tindergo  the  aqueous  fusion  when  heated.  The  salt  is  bitter  and  purgative  ; 
its  solution  is  alkaline  to  test-paper.  Crystals  containing  14  equivalents  of 
water,  and  having  a  form  different  from  that  above  mentioned,  have  been 
obtained. 

A  second  tribasic  phosphate,  sometimes  called  subphosphate,  8NaO, 
P05-}-24HO,  is  obtained  by  adding  a  solution  of  caustic  soda  to  the  prece- 
ding salt.  The  crystals  are  slender  six-sided  prisms,  soluble  in  5  parts  of 
cold  water.  It  is  decomposed  by  acids,  even  carbonic,  but  suffers  no  change 
by  heat,  except  the  loss  of  its  water  of  crystallization.  Its  solution  is  strongly 
alkaline.  A  third  tribasic  phosphate,  often  called  superphosphate  or  biphos- 
phate,  NaO,2HO,P05-f-2HO,  may  be  obtained  by  adding  phosphoric  acid  to 
the  ordinary  phosphate,  until  it  ceases  to  precipitate  chloride  of  barium,  and 
exposing  the  concentrated  solution  to  cold.  The  crystals  a»e  prismatic,  very 
soluble,  and  have  an  acid  reaction.  When  strongly  heated,  the  salt  becomes 
changed  into  monobasic  phosphate  of  soda. 

Tribasic  phosphate  of  soda,  ammonia,  and  water ;  microcosmic  salt,  NaO, 
NH^OjHOjPOg-j-SriO.  —  Six  parts  of  common  phosphate  of  soda  are  heated 
with  2  of  water  until  the  whole  is  liquefied,  when  1  part  of  powdered  sal- 
ammoniac  is  added ;  common  salt  separates,  and  may  be  removed  by  a  filter, 
and  from  the  solution,  duly  concentrated,  the  new  salt  is  deposited  in  pris- 
matic crystals,  which  may  be  purified  by  one  or  two  re-crystallizations. 
Microcosmic  salt  is  very  soluble.  When  gently  heated,  it  parts  with  the  8 
eq.  of  water  crystallization,  and,  at  a  higher  temperature,  the  water  acting 
as  base  is  expelled,  together  with  the  ammonia,  and  a  very  fusible  compound, 
metaphosphate  of  soda,  remains,  which  is  valuable  as  a  flux  in  blowpipe  ex- 
periments.    This  salt  is  said  to  occur  in  the  urine. 

BiBASic  phosphate  of  soda;  pyrophosphate  of  soda,  2  NaO.POj-j-lOHO. 
—  Prepared  by  strongly  heating  common  phosphate  of  soda,  dissolving  the 
residue  in  water,  and  re-crystallizing.  The  crystals  are  very  brilliant,  per- 
manent in  the  air,  and  less  soluble  than  the  original  phosphate ;  their  solution 
is  alkaline.  A  bibasic  phosphate,  containing  an  equivalent  of  basic  water, 
has  been  obtained  ;  it  does  not,  however,  crystallize. 

Monobasic  phosphate  of  soda;  metaphosphate  of  soda,  NaO,POg. — 
Obtained  by  heating  either  the  acid  tribasic  phosphate,  or  microcosmic  salt. 
It  is  a  transparent  glassy  substance,  fusible  at  a  dull  red-heat,  deliquescent, 
and  very  soluble  in  water.  It  refuses  to  crystallize,  but  dries  up  into  a 
gum-like  mass. 

If  this  glassy  phosphate  be  cooled  very  slowly  a  beautifully  crystalline 
mass  IS  obtained.  It  may  be  separated  by  means  of  boiling  water  from  the 
vitreous  metaphosphate  which  will  not  crystallize.  Another  metaphosphate 
has  been  obtained  by  adding  sulphate  of  soda  to  an  excess  of  phosphoric  acid, 
evaporating  and   heating  to  upwards  of  600°  (315°'5C).      Possibly  these 


SODIUM.  231 

several  metamosphates  may  be  represented  by  the  formulae  NaOjPOj ; 
2NaO,2P05;  SNaCSPOg. 

The  tribasic  phosphates  give  a  bright  yellow  precipitate  with  solution  of 
nitrate  of  silver ;  the  bibasic  and  monobasic  phosphates  afford  white  precipi- 
tates with  the  same  substance.  The  salts  of  the  two  latter  classes,  fused 
with  excess  of  carbonate  of  soda,  yield  the  tribasic  modification  of  the  acid. 

Phosphates  intermediate  between  the  monobasic  and  bibasic  phosphates  of  soda, 
3NaO,2P05,  and  6NaO,r)P05.  —  The  first  is  produced  by  fusing  100  parts  of 
anhydrous  pyrophosphate  of  soda,  and  76-87  parts  of  metaphosphate  of  soda. 
The  white  crystalline  mass  is  reduced  to  powder,  and  quickly  exhausted  with 
water.  The  solution,  on  exposure  to  the  atmosphere,  yields  small  plates  which 
are  very  soluble  in  water. 

The  second  is  produced  by  fusing  100  parts  of  pyrophosphate  of  soda,  and 
307-5  of  metaphosphate;  it  crystallizes  with  more  difficulty  than  the  prece- 
ding compound. 

MM.  Fleitmann  and  Henneberg,  the  discoverers  of  these  new  phosphates, 
represent  the  different  phosphates  thus :  — 

Common  phosphate 6NaO,2P05 

Pyrophosphate 6NaO,3P06 

New  phosphates  teNaO.SPO* 

Metaphosphate  6NaO,6P05 

In  each  of  which  six  equivalents  of  the  base  are  combined  with  a  different 
polymeric  acid. 

BiBOBATE  OF  SODA;  BOHAX,  NaO,2BO34-10HO. — This  compound  occurs 
in  the  waters  of  Qertain  lakes  in  Thibet  and  Persia  ;  it  is  imported  in  a  crude 
state  from  the  East  Indies  under  the  name  of  tincal.  When  purified,  it  con- 
stitutes the  borax  of  commerce.  Much  borax  is  now,  however,  manufactured 
from  the  native  boracic  acid  of  Tuscany.  Borax  crystallizes  in  six-sided 
prisms,  which  effloresce  in  dry  air,  and  require  20  parts  of  cold,  and  6  of 
boiling  water  for  solution.  Exposed  to  heat,  the  10  eq.  of  water  of  crystal- 
lization are  expelled,  and  at  a  higher  temperature  the  salt  fuses,  and  assumes 
a  glassy  appearance  on  cooling ;  in  this  state  it  is  much  used  for  blowpipe 
experiments,  the  metallic  oxides  dissolving  in  it  to  transparent  beads,  many 
of  which  are  distingiiished  by  characteristic  colours.  By  particular  manage- 
ment, crystals  of  borax  can  be  obtained  with  5  eq.  of  water ;  they  are  very 
hard,  and  permanent  in  the  air.  Although  by  constitution  an  acid  salt, 
borax  has  an  alkaline  reaction  to  test-paper.  It  is  used  in  the  arts  for  sol- 
dering metals,  its  action  consisting  in  rendering  the  surfaces  to  be  joinea 
metallic,  by  dissolving  the  oxides,  and  sometimes  enters  into  the  composition 
of  the  glaze  with  which  stoneware  is  covered. 

Neutral  borate  of  soda  may  be  formed  by  fusing  together  borax  and  car- 
bonate of  soda  in  equivalent  proportions,  and  then  dissolving  the  mass  in 
water.     The  crystals  are  large,  and  contain  NaO,B03-}-8HO. 

Sulphide  of  sodium,  NaS.  —  Prepared  in  the  same  manner  as  the  proto- 
salphide  of  potassium ;  it  separates  from  a  concentrated  solution  in  octahe- 
dral crystals,  which  are  rapidly  decomposed  by  contact  of  air  into  a  mixture 
of  hydrate  and  hyposulphite  of  soda.  It  forms  double  sulphur-salts  with 
sulphuretted  hydrogen,  bisulphide  of  carbon,  and  other  sulphur-acids. 

Sulphide  of  sodium  is  supposed  to  enter  into  the  composition  of  the  beau- 
tiful pigment  ultramarine,  prepared  from  the  laj>is  lazuli,  and  which  is  now 
>mitated  by  artificial  means.* 

Chloride  op  sodium  ;  commox  salt,  NaCl.  —  This  very  important  sub- 

•  See  Pharmaceutical  Journal,  ii.  53. 


232  AMMONIUM. 

stance  is  found  in  many  parts  of  the  world  in  solid  beds  or  ii'regular  strata 
of  immense  thickness,  as  in  Clieshire,  for  example,  in  Spain,  Galicia,  and 
many  other  localities.  An  inexhaustible  supply  exists  also  in  the  waters  of 
the  ocean,  and  large  quantities  are  annually  obtained  from  saline  springs. 

The  rock-salt  is  almost  always  too  impure  for  use ;  if  no  natural  brine- 
spring  exist,  an  artificial  one  is  formed  by  sinking  a  shaft  into  the  rock-salt, 
and,  if  necessary,  introducing  water.  This,  when  saturated,  is  pumped  up, 
and  evaporated  more  or  less  rapidly  in  large  iron  pans.  As  the  salt  sepa- 
rates, it  is  removed  from  the  bottom  of  the  vessels  by  means  of  a  scoop, 
pressed  while  still  moist  into  moulds,  and  then  transferred  to  the  drying- 
stove.  When  large  crystals  are  required,  as  for  the  coarse-grained  bay-salt 
used  in  curing  provisions,  the  evaporation  is  slowly  conducted.  Common 
salt  is  apt  to  be  contaminated  with  chloride  of  magnesium. 

When  pure,  this  substance  is  not  deliquescent  in  moderately  dry  air.  It 
crystallizes  in  anhydrous  cubes,  which  are  often  grouped  together  into  pyra- 
mids, or  steps.  It  requires  about  2J  parts  of  water  at  60°  (15°-5C)  for  solu- 
tion, and  its  solubility  is  not  sensibly  increased  by  heat ;  it  dissolves  to  some 
extent  in  spirits,  but  is  nearly  insoluble  in  absolute  alcohol.  Chloride  of 
sodium  fuses  at  a  red-heat,  and  is  volatile  at  a  still  higher  temperature.  The 
economical  uses  of  common  salt  are  well  known. 

The  iodide  and  bromide  of  sodium  much  resemble  the  corresponding  potas- 
sium-compounds :  they  crystallize  in  cubes  which  are  anhydrous,  and  are 
very  soluble  in  water. 


There  is  no  good  precipitant  for  soda,  all  the  salts  being  very  soluble  with 
the  exception  of  antimonate  of  soda,  the  use  of  which  is  attended  with  diifi- 
culties ;  its  presence  is  often  determined  by  purely  negative  evidence.  The 
yellow  colour  imparted  by  soda-salt  to  the  outer  flame  of  the  blowpipe,  and 
to  combustible  matter,  is  a  character  of  some  importance. 

AMMONIUM. 

In  connection  with  the  compounds  of  potassium  and  sodium,  those  formed 
by  ammonia  are  most  conveniently  studied.  Ammoniacal  salts  correspond 
in  every  respect  in  constitution  with  those  of  potassa  and  soda ;  in  all  cases 
the  substance  which  replaces  those  alkalis  is  hydrate  of  ammonia,  or,  as  it 
IS  now  almost  generally  considered,  the  oxide  of  a  hypothetical  substance 
called  ammonium,  capable  of  playing  the  part  of  a  metal,  and  ismorphous 
with  potassium  and  sodium.  All  attempts  to  isolate  this  substance  have 
failed,  apparently  from  its  tendency  to  separate  into  ammonia  and  hydrogen 
gas. 

When  a  globule  of  mercury  is  placed  on  a  piece  of  moistened  caustic  po- 
tassa, and  connected  with  the  negative  side  of  a  voltaic  battery  of  very 
moderate  power,  while  the  circuit  is  completed  through  the  platinum  plate 
upon  which  rests  the  alkali,  decomposition  of  the  latter  takes  place,  and  an*^ 
amalgam  of  potassium  is  rapidly  formed. 

If  this  experiment  be  now  repeated  with  a  piece  of  sal-ammoniac  instead 
of  hydrate  of  potassa,  a  soft  solid,  metalline  mass  is  also  produced,  which 
has  been  called  the  ammoniacal  amalgam,  and  considered  to  contain  ammo- 
nium in  combination  with  mercury.  A  still  simpler  method  of  preparing 
this  extraordinary  compound  is  the  following : — A  little  mercury  is  put  into 
a  test-tube  with  a  grain  or  two  of  potassium  or  sodium,  and  gentle  heat  ap- 
plied; combination  ensues,  attended  by  heat  and  light.  When  cold,  the 
fluid  amalgam  is  put  into  a  capsule,  and  covered  with  a  strong  solution  of 
sal-ammoniac.  The  production  of  ammoniacal  amalgam  instantly  com- 
mences, tlie  mercury  increases  prodigiously  in  vclume,  and  becomes  quite 


AMMONIUM.  233 

pasty.     The  increase  of  weight  is,  however,  quite  trifling ;  it  varies  from 

Left  to  itself,  the  amalgam  quickly  decomposes  into  fluid  mercury,  ammo- 
nia, and  hydrogen. 

It  is  difficult  to  ofter  any  opinion  concerning  the  real  nature  of  this  com- 
pound :  something  analogous  occurs  when  pure  silver  is  exposed  to  a  very 
high  temperature,  much  above  its  melting-point,  in  contact  with  air  or  oxy- 
gen gas ;  the  latter  is  absorbed  in  very  large  quantity,  amounting,  accord 
ing  to  the  observation  of  Gay-Lussac,  to  20  times  the  volume  of  the  silver, 
and  is  again  disengaged  on  lessening  the  heat.  The  metal  loses  none  of  its 
lustre,  and  is  not  sensibly  altered  in  other  respects. 

The  great  argument  in  favour  of  the  existence  of  ammonium  is  founded 
on  the  perfect  comparison  which  the  ammoniacal  salts  bear  with  those  of 
the  alkaline  metals. 

The  equivalent  of  ammonium  is  18 ;  its  symbol  is  NH^. 

Chloride  of  ammonium;  (Muriate  of  Ammonia;)  sal-ammoniac,  NH^Cl. 
— Sal-ammoniac  was  formerly  obtained  from  Egypt,  being  extracted  by  sub- 
limation from  the  soot  of  camels'  dung;  it  is  now  largely  manufactured  from 
the  ammoniacal  liquid  of  the  gas-works,  and  from  the  condensed  products 
of  the  distillation  of  bones,  and  other  animal  refuse,  in  the  preparation  of 
animal  charcoal. 

These  impure  and  highly  offensive  solutions  are  treated  with  slight  excess 
of  hydrochloric  acid,  by  which  the  alkali  is  neutralized,  and  the  carbonate 
and  sulphide  decomposed  with  evolution  of  carbonic  acid  and  sulphuretted 
hydrogen  gases.  The  liquid  is  evaporated  to  dryness,  and  the  salt  carefully 
heated,  to  expel  or  decompose  the  tarry  matter ;  it  is  then  purified  by  sub- 
limation in  large  iron  vessels  lined  with  clay,  surmounted  with  domes  of  lead. 

Sublimed  sal-ammoniac  has  a  fibrous  texture,  it  is  tough,  and  difficult  to 
powder. 

When  crystallized  from  water  it  separates'under  favourable  circumstances, 
in  distinct  cubes  or  octahedrons ;  but  the  crystals  are  usually  small,  and  ag- 
gregated together  in  rays.  It  has  a  sharp  saline  taste,  and  is  soluble  in  2^ 
parts  of  cold,  in  a  much  smaller  quantity  of  hot  water.  By  heat,  it  is  sub- 
limed without  decomposition.  The  crystals  are  anhydrous.  Chloride  of 
ammonium  forms  double  salts  with  chloride  of  magnesium,  nickel,  cobalt, 
manganese,  zinc,  and  copper. 

Sulphate  of  oxide  op  ammonium  ;  sulphate  of  ammonia,  NH^O, 
SOg-j-HO.  —  Prepared  by  neutralizing  carbonate  of  ammonia  by  sulphuric 
acid,  or  on  a  large  scale,  by  adding  sulphuric  acid  in  excess  to  the  coal-gas 
liquor  just  mentioned,  and  purifying  the  product  by  suitable  means.  It  is 
soluble  in  2  parts  of  cold  water,  and  crystallizes  in  long,  flattened,  six-sided 
prisms,  which  lose  an  equivalent  of  water  when  heated.  It  is  entirely  de- 
composed, and  driven  off  by  ignition,  and,  even  to  a  certain  extent,  by  long 
boiling  with  water,  ammonia  being  expelled  and  the  liquid  rendered  acid. 

Carbonates  of  ammonia.  —  These  compounds  have  been  carefully  exam- 
ined by  Professor  Rose,  of  Berlin,'  and  appear  very  numerous.  The  neutral^ 
anhydrous  carbonate,  NHgjCOj,  is  prepared  by  the  direct  union  of  carbonic 
acid  with  ammoniacal  gas,  both  being  carefully  cooled.  The  gases  combine 
in  the  proportions  of  one  measure  of  the  first  to  two  of  the  second,  and  give 
rise  to  a  pungent,  and  very  volatile  compound,  which  condenses  in  white 
flocks.  It  is  very  soluble  in  water.  The  pungent,  transparent,  carbonate 
of  ammonia  of  pharmacy,  which  is  prepared  by  subliming  a  mixtiire  of  sal- 
ammoniac  and  chalk,  always  contains  less  base  than  that  required  to  form 
a  neutral  carbonate.     Its  composition  vaines  a  good  deal,  but  in  freshly  pre- 

*  Annalen  der  Pharmacie,  xxx.  45 
20* 


234  AMMONIUM. 

pared  specimens  approaches  that  of  a  sesquicarbonate  of  oxide  of  ammonium, 
2  NH^OjSCOj. — When  heated  in  a  retort,  the  neck  of  which  dips  into  mer- 
cury, it  is  decomposed,  with  disengagement  of  pure  carbonic  acid,  into 
neutral  hydrated  carbonate  of  ammonia,  and  several  other  compounds.  Ex- 
posed to  the  air  at  common  temperatures,  it  disengages  neutral  carbonate 
of  ammonia,  loses  its  pungency,  and  crumbles  down  to  a  soft,  white  powder, 
which  is  a  bicarbonate,  containing  NH40,C02+HO,C02.  This  is  a  permanent 
combination,  although  still  volatile.  When  a  strong  solution  of  the  commer- 
cial sesquicarbonate  is  made  with  tepid  water,  and  filtered,  warm,  into  a 
close  vessel,  large  and  regular  crystals  of  bicarbonate,  having  the  above  com- 
position, are  sometimes  deposited  after  a  few  days.  These  are  inodorous, 
quite  permanent  in  the  air,  and  resemble,  in  the  closest  manner,  crystals  of 
bicarbonate  of  potassa. 

Nitrate  of  oxide  of  Ammonium;  nitrate  of  ammonia,  NH40,N05. — 
Easily  prepared  by  adding  carbonate  of  ammonia  to  slightly  diluted  nitric 
acid  until  neutralization  has  been  reached.  By  slow  evaporation  at  a  mode- 
rate temperature  it  crystallizes  in  six-sided  prisms,  like  those  of  nitrate  of 
potassa ;  but,  as  usually  prepared  for  making  nitrous  oxide,  by  quick  boiling, 
until  a  portion  solidifies  completely  on  cooling,  it  forms  a  fibrous  and  indis- 
tinct crystalline  mass. 

Nitrate  of  ammonia  dissolves  in  2  parts  of  cold  water,  is  but  feebly  deli- 
quescent, and  deflagrates  like  nitre  on  contact  with  heated  combustible 
matter.     Its  decomposition  by  heat  has  been  already  explained.* 

Sulphides  of  Ammonium.  —  Several  of  these  compounds  exist,  and  may 
be  formed  by  distilling  with  sal-ammoniac  the  corresponding  sulphides  of 
potassium  or  sodium» 

The  double  sulphide  of  ammonium  and  hydrogen,  NH^S-f-HS,  commonly 
called  hydrosulphate  of  ammonia,  or,  more  correctly,  hydrosulphate  of  sul- 
phide of  ammonium,  is  a  compound  of  great  practical  utility  ;  it  is  obtained 
by  saturating  a  solution  of  ammonia  with  well-washed  sulphuretted  hydrogen 
gas,  until  no  more  of  the  latter  is  absorbed.  The  solution  is  nearly  colourless 
at  first,  but  becomes  yellow  after  a  time,  without,  however,  sufiTering  material 
injury,  unless  it  has  been  exposed  to  the  air.  It  gives  precipitates  with  most 
metallic  solutions,  which  are  very  often  characteristic,  and  is  of  great  service 
in  analytical  chemistry.'' 


When  dry  ammoniacal  gas  is  brought  in  contact  with  anhydrous  sulphuric 
acid,  a  white  crystalline  compound  is  produced,  which  is  soluble  in  water. 
In  a  freshly  prepared  cold  solution  of  this  substance  neither  sulphuric  acid 
nor  ammonia  can  be  found  ;  but  after  standing  some  time,  and  especially  if 
heat  be  applied,  it  passes  into  ordinary  sulphate  of  ammonia. 

A  compound  of  dry  ammoniacal  gas  and  sulphurous  acid  also  exists  ;  it  is 
a  yellow  soluble  substance,  altogether  distinct  from  sulphite  of  ammonia. 

» Page  125. 

^Phosphates  of  Oxide  op  Ammonium;  Common  Tribasic  Phosphate,  2  NH40,H0,P05-f-H0. — 
This  salt  is  formed  by  precipitating  the  acid  phosphate  of  lime  with  an  excess  of  carbonate 
of  ammonia.  The  solution  is  allowed  to  evaporate  spontaneously  or  by  a  gentle  heat.  In 
the  latter  case  ammonia  is  lost  and  it  becomes  necessary  to  saturate  the  acid  set  free,  previous 
to  crystallization.  It  crystallizes  in  six-sided  tables  derived  from  obliqiie  quadrangular 
prisms.  Its  crystals  are  eflBlorescent,  soluble  in  alcohol,  and  soluble  in  four  times  its  weight 
of  cold  water.  Its  solution  has  an  alkaline,  slightly  saline  taate  and  alkaline  reaction.  By 
heat  ammonia  is  disengaged. 

The  acid  tribasic  phosphate,  NH40,2HO,P06+4HO,  is  formed  when  a  solution  of  the  common 
phosphate  is  boiled  as  long  as  ammonia  is  given  oflf.  It  crystallizes  in  four-sided  prisms.  Its 
crystals  aie  permanent,  soluble  in  5  parts  of  cold  water,  acid  in  taste  and  reaction. 

Another  tribasic  phosphate,  3NH40,P06  subphosphate  is  formed  by  adding  ammonia  to 
either  of  tne  abov9     It  falls  as  a  slightly  soluble  granular  precipitate.— R.  B. 


LITHIUM.  235 

Dry  carbonic  acid  and  ammonia  also  unite  to  form  a  volatile  white  powder, 
as  already  mentioned. 

When  certain  salts,  especially  chlorides  in  an  anhydrous  state,  are  exposed 
to  ammoniacal  gas,  the  latter  is  absorbed  with  great  energy,  and  the  combi- 
nations formed  are  not  always  easily  decomposed  by  heat.  The  chlorides  of 
copper  and  silver  absorb,  in  this  manner,  large  quantities  of  the  gas.  All 
these  compounds  must  be  carefully  distinguished  from  the  true  ammoniacal 
salts  containing  ammonium  or  its  oxide. 

There  is  supposed  to  be  yet  another  compound  of  hydrogen  and  nitrogen 
to  which  the  term  amidogen  has  been  given.  When  potassium  is  heated  in 
the  vapour  of  water,  this  substance  is  decomposed,  hydrogen  is  evolved,  and 
the  metal  converted  into  oxide.  When  the  same  experiment  is  made  with 
dry  ammoniacal  gas,  hydrogen  is  also  set  free,  and  an  olive-green  crystalline 
compound  produced,  supposed  to  contain  potassium  in  union  with  a  new  body, 
NHg,  having  an  equivalent  of  hydrogen  less  than  ammonia. 

When  ammonia  is  added  to  a  solution  of  corrosive  sublimate,  a  white  pre- 
cipitate is  obtained,  which  has  been  long  known  in  pharmacy.  Sir  R.  Kane 
infers,  from  his  experiments,  that  this  substance  should  be  looked  upon  as  a 
compound  of  chloride  of  mercury  with  amide  of  mercury.  The  latter  salt 
has  not  been  obtained  separately  ;  still  less  has  amidogen  itself  been  isolated. 

It  has  been  thought  that  ammonia  may  be  considered  an  amide  of  hydrogen, 
analogous  to  water  or  oxide  of  hydrogen,  capable  of  entering  into  combina- 
tion with  salts,  and  other  substances,  in  a  similar  manner,  yielding  unstable 
and  easily  decomposed  compounds,  which  offer  a  great  contrast  to  those  of 
the  energetic  quasi-nxQiiiX  ammonium ;  the  views  of  chemists  upon  this  sub- 
ject are,  however,  still  divided. 


The  ammoniacal  salts  are  easily  recognised ;  they  are  all  decomposed  or 
volatilized  by  a  high  temperature ;  and  when  heated  with  hydrate  of  lime, 
or  solution  of  alkaline  carbonate,  evolve  ammonia,  which  may  be  known  by 
its  odour  and  alkaline  reaction.  The  salts  are  all  more  or  less  soluble,  the 
acid  tartrate  of  ammonia  and  the  double  chloride  of  ammonium  and  platinum 
being  among  the  least  so ;  hence  the  salts  of  ammonia  cannot  be  distinguished 
from  those  of  potassa  by  the  tests  of  tartaric  acid  and  platinum-solution. 


A  connecting  link  between  this  class  of  metals  and  the  next  succeeding. 
Lithium  is  obtained  by  electrolyzing,  in  contact  with  mercury,  the  hydrate 
of  lithia,  and  then  decomposing  the  amalgam  by  distillation.  It  is  a  white 
metal  like  sodium,  and  very  oxidable.  The  equivalent  of  lithium  is  6-5,  and 
its  symbol  L. 

The  oxide,  lithia,  LO,  is  found  in  petalite,  spodumene,  lepidolite,  and  a 
few  other  minerals,  and  sometimes  occurs  in  minute  quantities  in  mineral 
springs.  From  petalite  it  may  be  obtained,  on  the  small  "scale,  by  the  fol- 
lowing process :  —  The  mineral  is  reduced  to  an  exceedingly  fine  powder, 
mixed  with  five  or  six  times  its  weight  of  pure  carbonate  of  lime,  and  the 
mixture  heated  to  whiteness,  in  a  platinum  crucible,  placed  within  a  well- 
covered  earthen  one,  for  twenty  minutes  or  half  an  hour.  The  shrunken 
coherent  mass  is  digested  in  dilute  hydrochloric  acid,  the  whole  evaporated 
to  dryness,  acidulated  water  added,  and  the  silica  separated  by  a  filter.  The 
solution  is  then  mixed  with  carbonate  of  ammonia  in  excess,  boiled  and 
filtered ;  the  clear  liquid  is  evaporated  to  dryness,  and  gently  heated  in  a 


236  LITHIUM. 

platinum  crucible,  to  expel  the  sal-ammoniac.  The  residue  is  then,  wetted 
"with  oil  of  vitriol,  gently  evaporated  once  more  to  dryness,  and  ignited ; 
pure  fused  sulphate  of  lithia  remains. 

This  process  will  serve  to  give  a  good  idea  of  the  general  nature  of  the 
operation  by  which  alkalis  are  extracted  in  mineral  analysis,  and  theii 
quantities  determined. 

The  hydrate  of  lithia  is  much  less  soluble  in  water  than  those  of  potassa 
and  soda ;  the  carbonate  and  phosphate  are  also  sparingly  soluble  salts. 
The  chloride  crystallizes  in  anhydrous  cubes  which  are  deliquescent.  Sul- 
phate of  lithia  is  a  very  beautiful  salt ;  it  crystallizes  in  lengthened  prisms 
containing  one  equivalent  of  water.  It  gives  no  double  salt  with  sulphate 
of  alumina. 

The  salts  of  lithia  colour  the  outer  flame  of  the  blowpipe  carmine-red. 


BARIUM.  237 


SECTION  II. 
METALS  OF  THE  ALKALINE  EARTHS. 


Barium  was  obtained  by  Sir  H.  Davy  by  means  similar  to  those  mentioned 
in  the  case  of  lithium ;  it  is  procured  more  advantageously,  by  strongly  heat- 
ing baryta  in  an  iron  tube,  through  which  the  vapour  of  potassium  is  con- 
veyed. The  reduced  barium  is  extracted  by  quicksilver,  and  the  amalgam 
distilled  in  a  small  green  glass  retort. 

Barium  is  a  white  metal,  having  the  colour  and  lustre  of  silver ;  it  is  mal- 
leable, melts  below  a  red  heat,  decomposes  water,  and  gradually  oxidizes  in 
the  air. 

The  equivalent  of  this  metal  has  been  fixed  at  68-5 ;  its  symbol  is  Ba. 

Pkotoxide  of  barium;  baryta,  BaO.  —  Baryta,'  or  barytes,  occurs  in 
nature  in  considerable  abundance  as  carbonate  and  sulphate,  forming  the 
veinstone  in  many  lead-mines ;  from  both  these  sources  it  may  be  extracted 
with  facility.  The  best  method  of  preparing  pure  baryta  is  to  decompose 
the  crystallized  nitrate  by  heat  in  a  capacious  crucible  of  porcelain  until  red 
vapours  are  no  longer  disengaged ;  the  nitric  acid  is  resolved  into  nitrous 
acid  and  oxygen,  and  the  baryta  remains  behind  in  the  form  of  a  greyish 
spongy  mass,  fusible  at  a  high  degree  of  heat.  When  moistened  with  water, 
it  combines  to  a  hydrate  with  great  elevation  of  temperature. 

The  hydrate  is  a  white,  soft  powder,  having  a  great  attraction  for  carbonic 
acid,  and  soluble  in  20  parts  of  cold  and  2  of  boiling  water ;  a  hot  saturated 
solution  deposits  crystals  on  cooling,  which  contain  BaO,  H0-|-9H0.  Solu- 
tion of  hydrate  of  baryta  is  a  valuable  re-agent;  it  is  highly  alkaline  to 
test-paper,  and  instantly  rendered  turbid  by  the  smallest  trace  of  carbonio 
acid. 

BiNOXiDE  OF  BARIUM,  BaOg-  —  This  may  be  formed,  as  already  mentioned, 
by  exposing  baryta,  heated  to  full  redness  in  a  porcelain  tube,  to  a  current 
of  pure  oxygen  gas.  The  binoxide  is  grey,  and  forms  a  white  hydrate  with 
water,  which  is  not  decomposed  by  that  liquid  in  the  cold,  but  dissolves  in 
small  quantity.  The  binoxide  may  also  be  made  by  heating  pure  baryta  to 
redness  in  a  platinum  crucible,  and  then  gradually  adding  an  equal  weight 
of  chlorate  of  potassa;  binoxide  of  barium  and  chloride  of  potassium  are 
produced.  The  latter  may  be  extracted  by  cold  water,  and  the  binoxide 
left  in  the  state  of  hydrate.  It  is  interesting  chiefly  in  its  relation  to  bin- 
oxide of  hydrogen.  When  dissolved  in  dilute  acid,  it  is  decomposed  by 
bichromate  of  potassa,  oxide  of  silver,  chloride  of  silver,  sulphate  and  car 
bonate  of  silver. 

Chloride  of  barium,  BaCl+2H0.  —  This  valuable  salt  is  prepared  by 
dissolving  the  native  carbonate  in  hydrochloric  acid,  filtering  the  solution, 

»  From  /3ap«5j,  heavy,  in  allusiou  to  the  great  specific  gravity  of  the  native  carbonate  and 
•ulphale. 


238  BARIUM. 

and  evaporating  until  a  skin  begins  to  form  at  the  surface ;  the  solution  on 
cooling  deposits  crystals.  When  native  carbonate  cannot  be  procured,  the 
native  sulphate  may  be  employed  in  the  following  manner: — The  sulphate  is 
reduced  to  fine  powder,  and  intimately  mixed  with  one-third  of  its  weight 
of  powdered  coal ;  the  mixture  is  pressed  into  an  earthen  crucible  to  which 
a  cover  is  fitted,  and  exposed  for  an  hour  or  more  to  a  high  red-heat,  by 
which  the  sulphate  is  converted  into  sulphide  at  the  expense  of  the  com- 
bustible matter  of  the  coal.  The  black  mass  obtained  is  powdered  and  boiled 
in  water,  by  which  the  sulphide  is  dissolved ;  the  solution  is  filtered  hot,  and 
mixed  with  a  slight  excess  of  hydrochloric  acid ;  chloride  of  barium  and  sul- 
phuretted hydrogen  are  produced ;  the  latter  escaping  with  effervescence. 
Lastly,  the  solution  is  filtered  to  separate  any  little  insoluble  matter,  and  eva- 
porated to  the  crystallizing  point. 

The  crystals  of  chloride  of  barium  are  flat,  four-sided  tables,  colourless 
and  transparent.  They  contain  2  equivalents  of  water,  easily  driven  off  by 
heat;  100  parts  of  water  dissolve  43-5  parts  at  00°  (15o-5C),  and  78  parts 
at  223"  (106°-5C),  which  is  the  boiling-point  of  the  saturated  solution. 

Nitrate  of  baryta,  BaO,  NOj. — The  nitrate  is  prepared  by  methods 
exactly  similar  to  the  above,  nitric  acid  being  substituted  for  the  hydro- 
chloric. It  crystallizes  in  transparent  colourless  octahedrons,  which  are 
anhydrous.  They  require  for  solution  8  parts  of  cold,  and  3  parts  of  boil- 
ing water.  This  salt  is  much  less  soluble  in  dilute  nitric  acid  than  in  pure 
water ;  errors  sometimes  arise  from  such  a  precipitate  of  crystalline  nitrate 
of  baryta  being  mistaken  for  sulphate.  It  disappears  on  heating,  or  by  large 
affusion  of  water. 

Sulphate  of  baryta;  heavy-spar;  BaOjSOg. — Found  native,  often  beau- 
tifully crystallized.  This  compound  is  always  produced  when  sulphuric  acid 
or  a  soluble  sulphate  is  mixed  with  a  solution  of  a  barytic  salt.  It  is  not 
sensibly  soluble  in  water  or  in  any  dilute  acid,  even  nitric ;  hot  oil  of  vitriol 
dissolves  a  little,  but  the  greater  part  separates  again  on  cooling.  Sulphate 
of  baryta  is  used  as  a  pigment,  but  often  for  the  purpose  of  adulterating 
white-lead  ;  the  native  salt  is  ground  to  fine  powder  and  washed  with  dilute 
sulphuric  acid,  by  which  its  colour  is  improved,  and  a  little  oxide  of  iron 
probably  dissolved  out.  The  specific  gravity  of  the  natural  sulphate  is  as 
high  as  4-4  to  4-8. 

Sulphide  of  barium,  BaS.  —  The  protosulphide  of  barium  is  obtained  in 
the  manner  already  described;  the  higher  sulphides  may  be  formed  by  boil- 
ing this  compound  with  sulphur.  Protosulphide  of  barium  crystallizes  in 
thin  and  nearly  colourless  plates  from  a  hot  solution,  which  contain  water, 
and  are  not  very  soluble ;  they  are  rapidly  altered  by  the  air.  A  strong 
solution  of  sulphide  may  be  employed  in  the  preparation  of  hydrate  of  baryta, 
by  boiling  it  with  small  successive  portions  of  black  oxide  of  copper,  until  a 
drop  of  the  liquid  ceases  to  precipitate  a  salt  of  the  lead  black ;  the  liquid 
being  filtered,  yields,  on  cooling,  crystals  of  hydrate.  In  this  reaction,  besides 
hydrate  of  baryta,  hyposulphite  of  that  base,  and  sulphide  of  copper  are 
produced ;  the  latter  is  insoluble,  and  is  removed  by  the  filter,  while  most 
of  the  hyposulphite  remains  in  the  mother-liquor. 

Carbonate  of  baryta,  BaO,  COj. — The  natural  carbonate  is  called  withe- 
rite;  the  artificial  is  formed  by  precipitating  the  chloride  or  nitrate  with  an 
alkaline  carbonate,  or  carbonate  of  ammonia.  It  is  a  heavy,  white  powder, 
very  sparingly  soluble  in  water,  and  chiefly  useful  in  the  preparation  of  the 
rarer  baryta-salts. 


Solutions  of  hydrate  and  nitrate  of  baryta  and  of  the  chloride  of  barium 
are  constantly  kept  in  the  laboratory  as  chemical  tests,  the  first  being  em- 


STRONTIUM.  239 

ployed  to  eflFect  the  separation  of  carbonic  acid  from  certain  gaseous  mix- 
tures, and  the  two  latter  to  precipitate  sulphuric  acid  from  solution. 

The  soluble  salts  of  baryta  are  poisonous,  which  is  not  the  case  with 
those  of  the  base  next  to  be  described. 

STRONTIUM. 

The  metal  strontium  may  be  obtained  from  its  oxide  by  means  similar  to 
those  described  in  the  case  of  barium ;  it  is  a  white  metal,  heavy,  oxidizable 
n  the  air,  and  capable  of  decomposing  water  at  common  temperatures. 

The  equivalent  of  strontium  is  43-8,  and  its  symbol  is  Sr. 

Protoxide  of  strontium  ;  strontia  ;  SrO. — This  compound  is  best  pre- 
pared by  decomposing  the  nitrate  by  the  aid  of  heat ;  it  resembles  in  almost 
every  particular  the  earth  baryta,  forming,  like  that  substance,  a  white  hy- 
drate, soluble  in  water.  A  hot  saturated  solution  deposits  crystals  on  cool- 
ing, which  contain  10  equivalents  of  water.  The  hydrate  has  a  great  at- 
traction for  carbonic  acid. 

BiNOxiDE  OF  STRONTIUM,  Sr02.  —  The  binoxide  is  prepared  in  the  same 
manner  as  binoxide  of  barium  ;  it  may  be  substituted  for  the  latter  in  mak- 
ing binoxide  of  hydrogen. 

The  native  carbonate  and  sulphate  of  strontia,  met  with  in  lead-mines  and 
other  localities,  serve  for  the  preparation  of  the  various  salts  by  means  ex- 
actly similar  to  those  already  described  in  the  case  of  baryta ;  they  have  a 
very  feeble  degree  of  solubility  in  water. 

Chloride  of  strontium,  SrCl.  —  The  chloride  crystallizes  in  colourless 
needles  or  prisms,  which  are  slightly  deliquescent;^and  soluble  in  2  parts  of 
cold  and  still  less  of  boiling  water ;  they  are  also  soluble  in  alcohol,  and  the 
solution,  when  kindled,  burns  with  a  crimson  flame.  The  crystals  contain  6 
equivalents  of  water,  which  they  lose  by  heat ;  at  a  higher  temperature  the 
chloride  fuses. 

Nitrate  of  strontia,  SrOjNOg. — This  salt  crystallizes  in  anhydrous  oc- 
tahedrons, which  require  for  solution  5  parts  of  cold,  and  about  half  their 
weight  of  boiling  water.  It  is  principally  of- value  to  the  pyrotechnist,  who 
employs  it  in  the  composition  of  the  well-known  "red-fire."* 


This  is  a  silver-white  and  extremely  oxidable  metal,  obtained  with  great 
difficulty  by  means  analogous  to  those  by  which  barium  and  strontium  are 
procured. 

The  equivalent  of  calcium  is  20 ;  its  symbol  is  Ca. 

Protoxide  of  calcium  ;  lime  ;  CaO.  —  This  extremely  important  com- 
pound may  be  obtained  in  a  state  of  considerable  purity  by  heating  to  full 
redness,  for  some  time,  fragments  of  the  black  bituminous  marble  of  I>erby- 
shire  or  Kilkenny.  If  required  absolutely  pure,  it  must  be  made  by  ignit- 
ing to  whiteness,  in  a  platinum  crucible,  an  artificial  carbonate  of  lime,  pro- 
cured by  precipitating  the  nitrate  by  carbonate  of  ammonia.  Lime  in  an 
impure  state  is  prepared  for  building  and  agricultural  purposes  by  calcining 


*  Rei>-Fire  :—  Grns. 

Dry  nitrate  of  strontia 800 

Sulphur 225 

Chlorate  of  potassa 200 

Lampblack 60 


Green-Pire: —  Qma. 

Dry  nitrate  of  baryta 45c 

Sulphur 150 

Chlorate  of  potassa 100 

Lampblack 2f 


The  strontia  or  baryta-salt,  the  sulphur,  and  the  lampblack,  must  be  finely  powdered  and 
intimately  mixed,  after  which  the  chlorate  of  potassa  should  be  added  in  rather  coarse  pow- 
der, and  mixed  without  much  rubbing  with  the  other  ingredients.  The  red-fire  compoeiUoit 
has  Veen  known  to  ignite  spontaneously. 


240  CALCIUM. 

in  a  kiln  of  suitable  construction,  the  ordinary  limestones  which  abonnd  in 
many  districts ;  a  red-heat,  continued  for  some  hours,  is  sufficient  to  disen- 
gage the  whole  of  the  carbonic  acid.  In  the  best  contrived  lime-kilns  the 
process  is  carried  on  continuously,  broken  limestone  and  fuel  being  con- 
stantly thrown  in  at  the  top,  and  the  burned  lime  raked  out  at  intervals  from 
beneath.  Sometimes,  when  the  limestones  contain  silica,  and  the  heat  has 
been  very  high,  the  lime  refuses  to  slake,  and  is  said  to  be  over-burned ;  in 
this  case  a  portion  of  silicate  has  been  formed. 

Pure  lime  is  white,  and  often  of  considerable  hardness ;  it  is  quite  infusi- 
ble, and  phosphoresces,  or  emits  a  pale  light  at  a  high  temperature.  When 
moistened  with  water,  it  slakes  with  great  violence,  evolving  heat,  and 
crumbling  to  a  soft,  white,  bulky  powder,  which  is  a  hydrate  containing  a 
single  equivalent  of  water ;  the  latter  can  be  again  expelled  by  a  red-heat. 
This  hydrate  is  soluble  in  water,  but  far  less  so  than  either  the  hydrate  of 
baryta  or  of  strontia,  and  what  is  very  remarkable,  the  colder  the  water,  the 
larger  the  quantity  of  the  compound  which  is  taken  up.  A  pint  of  water  at 
60°  (15°-5C)  dissolves  about  11  grains,  while  at  212°  (100°C)  only  7  grains 
are  retained  in  solution.  The  hydrate  has  been  obtained  in  thin  delicate 
crystals  by  slow  evaporation  under  the  air-pump.  Lime-water  is  always 
prepared  for  chemical  and  phai*maceutical  purposes  by  agitating  cold  water 
with  excess  of  hydrate  of  lime  in  a  closely-stopped  vessel,  and  then,  after 
subsidence,  pouring  off  the  clear  liquid,  and  adding  a  fresh  quantity  of 
water,  for  another  occasion ; — there  is  not  the  least  occasion  for  filtering  the 
solution.  Lime-water  has  a  strong  alkaline  reaction,  a  nauseous  taste,  and 
when  exposed  to  the  air  becomes  almost  instantly  covered  with  a  pellicle  of 
carbonate,  by  absorption  of  carbonic  acid  from  the  atmosphere.  It  is  used, 
like  baryta-water,  as  a  test  for  that  substance,  and  also  in  medicine.  Lime- 
water  prepared  from  some  varieties  of  limestone  may  contain  potassa. 

The  hardening  of  mortars  and  cements  is  in  a  great  measure  due  to  the 
gradual  absorption  of  carbonic  acid  ;  but  even  after  a  very  great  length  of 
time,  this  conversion  into  carbonate  is  not  complete.  Mortar  is  known, 
under  favourable  circumstances,  to  acquire  extreme  hardness  with  age. 
Lime-cements  which  resist  the  action  of  water,  contain  the  oxides  of  iron, 
silica,  and  alumina ;  they  require  to  be  carefully  prepared,  and  the  stone  not 
over-heated.  When  ground  to  powder  and  mixed  with  water,  solidification 
speedily  ensues,  from  causes  not  yet  thoroughly  understood,  and  the  cement, 
once  in  this  condition,  is  unaffected  by  wet.  Parker's  or  Roman  cement  is 
made  in  this  manner  from  the  nodular  masses  of  calcareo-argillaceous  iron- 
stone found  in  the  London  clay.  Lime  is  of  great  importance  in  agriculture ; 
it  is  found  more  or  less  in  every  fertile  soil,  and  is  often  very  advantageously 
added  by  the  cultivator.  The  decay  of  vegetable  fibre  in  the  soil  is  promoted, 
and  other  important  objects,  as  the  destruction  of  certain  hurtful  compounds 
of  iron  in  marsh  and  peat-land,  is  often  attained.  The  addition  of  lime  pro- 
bably serves  likewise  to  liberate  potassa  from  the  insoluble  silicate  of  that 
base  contained  in  the  soil. 

BiNoxiDE  OF  Calcium,  CaOj.  —  This  is  stated  to  resemble  binoxide  of 
barium,  and  to  be  obtainable  by  a  similar  process. 

Chloride  of  calcium,  CaCl.  —  Usually  prepared  by  dissolving  marble  in 
hydrochloric  acid  ;  also  a  by-product  in  several  chemical  manufactures.  The 
salt  separates  from  a  strong  solution  in  colourless,  prismatic,  and  exceed- 
ingly deliquescent  crystals,  which  contain  6  equivalents  of  water.  By  heat 
this  water  is  expelled,  and  by  a  temperature  of  strong  ignition  the  salt  is 
fused.  The  crystals  reduced  to  powder  are  employed  in  the  production  of 
artificial  cold  by  being  mixed  with  snow  or  powdered  ice  ;  and  the  chloride, 
strongly  dried  or  in  a  fused  condition,  is  of  great  practical  use  in  desiccating 
gases,  for  which  purpose  the  latter  are  slowly  transmitted  through  tubes 


CALCIUM.  241 

filled  with  fragments  of  the  salt.  Chloride  of  calcium  is  also  freely  soluble 
in  alcohol,  which,  when  anhydrous,  forms  with  it  a  definite  crystallizable 
compound. 

Sulphide  of  calcium.  —  The  simple  sulphide  is  obtained  by  reducing 
sulphate  of  lime  at  a  high  temperature  by  charcoal  or  hydrogen  :  it  is  nearly 
colourless,  and  but  little  soluble  in  water.  —  By  boiling  together  hydrate  of 
lime,  water,  and  flowers  of  sulphur,  a  red  solution  is  obtained,  which  on 
cooling  deposits  crystals  of  bisulphide,  which  contain  water.  When  the 
sulphur  is  in  excess,  and  the  boiling  long  continued,  a  pentasulphide  is 
generated ;  hyposulphurous  acid  is,  as  usual,  formed  in  these  reactions. 

Phosphide  of  calcium. — When  the  vapour  of  phosphorus  is  passed  over 
fragments  of  lime  heated  to  redness  in  a  porcelain  tube,  a  chocolate-brown 
compound,  the  so-called  phosphide  of  lime,  is  produced.  This  substance  is 
probably  a  mechanical  mixture  of  phosphide  of  calcium,  and  phosphate  of 
lime.  It  yields  spontaneously  inflammable  phosphoretted  hydrogen  when 
put  into  water. ^ 

Sulphate  of  lime  ;  gypsum  ;  selenite  ;  CaO,  SO3. — Native  sulphate  of 
lime  in  a  crystalline  condition,  containing  2  equivalents  of  water,  is  found  in 
considerable  abundance  in  some  localities ;  it  is  often  associated  with  rock- 
salt.  When  regularly  crystallized,  it  is  termed  selenite.  Anhydrous  sulphate 
of  lime  is  also  occasionally  met  with.  The  salt  is  formed  by  precipitation 
when  a  moderately  concentrated  solution  of  chloride  of  calcium  is  mixed 
with  sulphuric  acid.  Sulphate  of  lime  is  soluble  in  about  500  parts  of  cold 
water,  and  its  solubility  is  a  little  increased  by  heat.  It  is  more  soluble  in 
water  containing  chloride  of  ammonium  or  nitrate  of  potassa.  The  solution 
is  precipitated  by  alcohol.  Gypsum,  or  native  hydrated  sulphate,  is  largely 
employed  for  the  purpose  of  making  casts  of  statues  and  medals,  and  also 
for  moulds  in  the  porcelain  and  earthenware  manufactures,  and  for  other 
applications.  It  is  exposed  to  heat  in  an  oven  where  the  temperature  does 
not  exceed  260°  (126° -eC),  by  which  the  water  of  crystallization  is  expelled, 
and  afterwards  reduced  to  fine  powder.  When  mixed  with  water,  it  solidifies 
after  a  short  time  from  the  re-formation  of  the  same  hydrate ;  but  this  effect 
does  not  happen  if  the  gypsum  has  been  over-heated.  It  is  often  called 
plaster  of  Paris.  Artificial  coloured  marbles,  or  scagliola,  are  frequently 
prepared  by  inserting  pieces  of  natural  stone  in  a  soft  stucco  containing  this 
substance,  and  polishing  the  surface  when  the  cement  has  become  hard. 
Sulphate  of  lime  is  one  of  the  most  common  impurities  of  spring  water. 

The  peculiar  property  water  acquires  by  the  presence  in  it  of  lime,  is 
termed  hardness.  It  manifests  itself  by  the  eflFect  such  waters  have  upon 
the  palate,  and  particularly  by  its  peculiar  behaviour  with  soap.  Hard 
waters  yield  a  lather  with  soap  only  after  the  whole  of  the  lime-salts  have 
been  thrown  down  from  the  water  in  the  form  of  an  insoluble  lime-soap. 
Upon  this  principle.  Prof.  Clark's  soap-test  for  the  hardness  of  waters  is 
based.'*  The  hardness  produced  by  sulphate  of  lime  is  called  pertnanent  hard- 
ness, since  it  cannot  be  remedied. 

Carbonate  of  lime  ;  chalk  ;  limestone  ;  marble  ;  CaO,  CO^.  —  Carbo- 
nate of  lime,  often  more  or  less  contaminated  by  protoxide  of  iron,  clay,  and 
organic  matter,  forms  rocky  beds,  of  immense  extent  and  thickness,  in 
almost  every  part  of  the  world.  These  present  the  greatest  diversities  of 
texture  and  appearance,  arising,  in  a  great  measure,  from  changes  to  which 

*  According  to  M.  Paul  Thenard,  the  phosphide  of  calcium  existing  in  this  mixture,  has 
the  compositions  PCaj.  By  coming  in  contact  with  water,  it  yields  liquid  phosphoretted 
hydrogen,  PCaa  +  2II0  =  2CaO  +  PH,—  (Page  166). 

The  greater  portion  of  the  liquid  phosphide  is  immediately  decomposed  into  solid  auil 
gaseous  phosphoretted  hydrogen.  — 5PH2  =  3PH3  +  F»H. 

*  Journal  of  the  Pharmaceutical  Society,  voi.  vi.  p.  b'iii. 

21 


242  CALCIUM. 

they  have  been  subjected  since  their  deposition.  The  most  ancient  and 
highly  crystalline  limestones  are  destitute  of  visible  organic  remains,  while 
those  of  more  recent  origin  are  often  entirely  made  up  of  the  shelly  exuviae 
of  once  living  beings.  Sometimes  these  latter  are  of  such  a  nature  as  to 
Bhow  that  the  animals  inhabited  fresh  -water ;  marine  species  and  corals  are, 
liowever,  most  abundant.  Cavities  in  limestone  and  other  rocks  are  very 
often  lined  with  magnificent  crystals  of  carbonate  of  lime  or  calcareous  spar, 
which  have  evidently  been  slowly  deposited  from  a  watery  solution.  Carbo- 
nate of  lime  is  always  precipitated  when  an  alkaline  carbonate  is  mixed  with 
a  solution  of  that  base. 

Although  this  substance  is  not  sensibly  soluble  *in  pure  water,  is  is  freely 
taken  up  when  carbonic  acid  happens  at  the  same  time  to  be  present.  If  9 
little  lime-water  be  poured  into  a  vessel  of  that  gas,  the  turbidity  first  pro- 
duced disappears  on  agitation,  and  a  transparent  solution  of  carbon»*te  of 
lime  in  excess  of  carbonic  acid  is  obtained.  This  solution  is  decomposeo 
completely  by  boiling,  the  carbonic  acid  being  expelled,  and  the  carbonate 
precipitated.  Since  all  natural  waters  contain  dissolved  carbonic  acid,  it  if 
to  be  expected  that  lime  in  this  condition  should  be  of  very  common  occur 
rence ;  and  such  is  really  found  to  be  the  fact ;  river,  and  more  especially 
spring  water,  almost  invariably  containing  carbonate  of  lime  thus  dissolved 
]n  limestone  districts,  this  is  often  the  case  to  a  great  extent.  The  hardnest 
of  water,  which  is  owing  to  the  presence  of  carbonate  of  lime,  is  called  tem- 
porary, since  it  is  diminished  to  a  very  considerable  extent  by  boiling,  ano 
may  be  nearly  removed  by  mixing  the  hard  water  with  lime-water,  when  both 
the  dissolved  carbonate  and  the  dissolved  lime,  which  becomes  thus  carbo- 
nated, are  precipitated.  Upon  this  principle,  Prof.  Clark's  process  of  soft- 
ening water  is  based.  This  process  is  of  considerable  importance,  since  a 
supply  of  hard  water  to  towns  is  in  many  respects  a  source  of  great  inconve- 
nience. As  has  been  already  mentioned,  the  use  of  such  water,  for  the  pur- 
poses of  washing,  is  attended  with  a  great  loss  of  soap.  Boilers  in  which 
such  water  is  heated,  speedily  become  lined  with  a  thick  stony  incrustation.* 
The  beautiful  stalactitic  incrustations  of  lime-stone  caverns,  and  the  deposits 
of  calc-siuter  or  travertin  upon  various  objects,  and  upon  the  ground  in  many 
places,  are  thus  explained  by  the  solubility  of  carbonate  of  lime  in  water 
containing  carbonic  acid. 

Crystallized  carbonate  of  lime  exhibits  the  curious  property  of  dimorphism ; 
calcareous  spar  and  arragonite,  although  possessing  the  same  chemical  com- 
position, both  containing  single  equivalents  of  lime  and  carbonic  acid,  and 
nothing  besides,  have  diflFerent  crystalline  forms,  diflFerent  densities,  and  dif- 
ferent optical  properties. 

The  former  occurs  very  abundantly  in  crystals  derived  from  an  obtuse 
rhomboid,  whose  angles  measure  106°  6''  and  74°  55'' :  its  density  varies  from 
2-5  to  2-8.  The  rarer  variety,  or  arragonite,  is  found  in  crystals  whose  pri- 
mary form  is  a  right  rhombic  prism ;  a  figure  having  no  geometrical  relation 
to  the  preceding ;  it  is,  besides,  heavier  and  harder. 

PiiOSPHATES  OF  LIME. — A  number  of  distinct  compounds  of  lime  and  phos- 
phoric acid  probably  exist.  Two  trihasic  phosphates,  2CaO,HO,P05,  and 
^CaOPOg,  are  produced  when  the  corresponding  soda-salts  are  added  in  so- 
lution to  chloride  of  calcium  ;  the  first  is  slightly  crystalline,  and  the  second 
gelatinous.  When  the  first  phosphate  is  digested  with  ammonia,  or  dissolved 
in  acid  and  re-precipitated  by  that  alkali,  it  is  converted  into  the  second. 

*  Many  proposals  have  been  made  to  prevent  the  formation  of  boiler-deposits.  The  most 
efficient  appears  to  be  the  method  of  Dr.  Ritterband,  which  consists  in  throwing  into  the 
boiler  a  small  quantity  of  sal-ammoniac,  when  carbonate  of  ammonia  is  formed,  which  is 
TolatiUzed  with  the  steam,  cBioride  of  calcium  remaining  in  solution.  It  need  scarcely  be 
i!»ontioned  that  this  plan  is  inapplicable  in  the  case  of  permanently  hard  waters. 


CALCIUM.  24ii 

Tne  earth  of  bones  consists  principally  of  what  appears  to  be  a  combi- 
nation of  these  two  salts.  Another  phosphate,  containing  2  equivalents 
of  basic  water,  has  been  described,  which  completes  the  series ;  it  is  formed 
by  dissolving  either  of  the  preceding  in  phosphoric,  hydrochloric,  or  nitric 
acid,  and  evaporating  until  the  salt  separates  on  cooling  in  small  platy  crys- 
tals. It  is  this  substance  which  yields  phosphorus,  when  heated  with  chai*- 
coal,  in  the  ordinary  process  of  manufacture  before  described.  Bibasic  and 
monobasic  phosphates  of  lime  also  exist.  '  These  phosphates,  although  inso- 
luble in  water,  dissolve  readily  in  dilute  acids,  even  acetic  acid. 

Fluoeide  OF  calcium;  fluor-spae;  CaF.  —  This  substance  is  important 
as  the  most  abundant  natural  source  of  hydrofluoric  acid  and  the  other 
fluorides.  It  occurs  beautifully  crystallized,  in  various  colours,  in  lead-veins, 
the  crystals  having  commonly  the  cubic,  but  sometimes  the  octahedral  form, 
parallel  to  the  faces  of  which  latter  figure  they  always  cleave.  Some  varie- 
ties, when  heated,  emit  a  greenish  phosphorescent  light.  The  fluoride  is 
quite  insoluble  in  water,  and  is  decomposed  by  oil  of  vitriol  in  the  manner 
already  mentined,  vide  p.  149. 

Chloeide  of  lime  ;  bleaching-powder.  —  When  hydrate  of  lime,  very 
slightly  moist,  is  exposed  to  chlorine  gas,  the  latter  is  eagerly  absorbed,  and 
a  compound  produced  which  has  attracted  a  great  deal  of  attention  ;  this  is 
the  bleaching-powder  of  commerce,  now  manufactured  on  an  immense  scale, 
for  bleaching  linen  and  cotton  goods.  It  is  requisite,  in  preparing  this  sub- 
stance, to  avoid  with  the  gi-eatest  care  all  elevation  of  temperature,  which 
may  be  easily  done  by  slowly  supplying  the  chlorine  in  the  first  instance. 
The  product,  when  freshly  and  well  prepared,  is  a  soft,  white  powder,  which 
attracts  moisture  from  the  air,  and  exhales  an  odour  sensibly  diflferent  from 
that  of  chlorine.  It  is  soluble  in  about  10  parts  of  water,  the  unaltered  hy- 
drate being  left  behind ;  the  solution  is  highly  alkaline,  and  bleaches  feebly. 
When  hydrate  of  lime  is  suspended  in  cold  water,  and  chlorine  gas  trans- 
mitted through  the  mixture,  the  lime  is  gradually  dissolved,  and  the  same 
peculiar  bleaching  compound  produced ;  the  alkalis  also,  either  caustic  or 
carbonated,  may  by  similar  means  be  made  to  absorb  a  large  quantity  of 
chlorine,  and  give  rise  to  corresponding  compounds ;  such  are  the  "  disinfect- 
ing solutions"  of  M.  Labarraque. 

The  most  consistent  view  of  the  constitution  of  these  curious  compounds 
is  that  which  supposes  them  to  contain  salts  of  hypochlorous  acid,  a  substance 
as  remarkable  for  bleaching  powers  as  chlorine  itself;  and  this  opinion  seems 
borne  out  by  a  careful  comparison  of  the  properties  of  the  bleaching-salts 
with  those  of  the  true  hypochlorites.  Hypochlorous  acid  can  be  actually  ob- 
tained from  good  bleaching-powder,  by  distilling  it  with  dilute  sulphuric  or 
nitric  acid,  in  quantity  insuflScient  to  decompose  the  whole ;  when  the  acid  is 
used  in  excess,  chlorine  is  disengaged.' 

If  this  view  be  correct,  chloride  of  calcium  must  be  formed  simultaneously 
with  the  hypochlorite,  as  in  the  following  diagram : — 

Chlorine —^Chloride  of  calcium. 

Lime  I  SY?^"" 
%                   I  Calcium 
Chlorine 
Lime  "  '"--^^^^^"^•Hypochlorite  of  lime. 

When  the  temperature  of  the  hydrate  of  lime  has  risen  during  the  absorption 
of  the  chlorine,  or  when  the  compound  has  been  subsequently  exposed  to 
heat,  its  bleaching  properties  are  impaired  or  altogether  destroyed  ;  it  then 
contains  chlorate  of  lime  and  chloride  of  calcium ;  oxygen,  in  variable  quan- 

•  M.  Gay-Lussac,  Ann.  Chim.  et  Phys.  3rd  serios,  v.  296 


244  CALCIUM. 

tity,  is  usuxtlly  set  free.  The  same  change  seems  to  ensue  by  long  keeping, 
even  at  the  common  temperature  of  the  air.  In  an  open  vessel  it  is  speedily 
destroyed  by  the  carbonic  acid  of  the  atmosphere.  Commercial  bleaching- 
powder  thus  constantly  varies  in  value  with  its  age,  and  with  the  care  origi- 
nally bestowed  upon  its  preparation ;  the  best  may  contain  about  30  per  cent, 
of  available  chlorine,  easily  liberated  by  an  acid,  which  is,  however,  far  short 
of  the  theoretical  quantity. 

The  general  method  in  which  this  substance  is  employed  for  bleaching  is 
the  following : — the  goods  are  first  immersed  in  a  dilute  solution  of  chloride 
of  lime  and  then  transferred  to  a  vat  containing  dilute  sulphuric  acid.  De- 
composition ensues ;  both  the  lime  of  the  hypochlorite  and  the  calcium  of 
the  chloride  are  converted  into  sulphate  of  lime,  while  the  free  hypochlorous 
and  hydrochloric  acids  yield  water  and  free  chlorine. 

The  chlorine  thus  disengaged  in  contact  with  the  cloth,  causes  the  destruc- 
tion of  the  colouring  matter.  This  process  is  often  repeated,  it  being  unsafe 
to  use  strong  solutions.  White  patterns  are  on  this  principle  imprinted  upon 
coloured  cloth,  the  figures  being  stamped  with  tartaric  acid  thickened  with 
gum-water,  and  then  the  stufi"  immersed  in  the  chloride  bath,  when  the 
parts  to  which  no  acid  has  been  applied  remain  unaltered,  while  the  printed 
portions  are  bleached. 

For  purifying  an  offensive  or  infectious  atmosphere,  as  an  aid  to  proper 
ventilation,  the  bleaching-powder  is  very  convenient.  The  solution  is  exposed 
in  shallow  vessels,  or  cloths  steeped  in  it  are  suspended  in  the  apartment, 
when  the  carbonic  acid  of  the  air  slowly  decomposes  it  in  the  manner  above 
described.  An  addition  of  a  strong  acid  causes  rapid  disengagement  of 
chlorine. 

The  value  of  any  sample  of  bleaching-powder  may  be  easily  determined  by 
the  following  method,  in  which  the  loosely  combined  chlorine  is  estimated 
by  its  efi'ect  in  peroxidizing  a  protosalt  of  iron,  of  which  two  equivalents  re- 
quire one  of  chlorine ;  the  latter  acts  by  decomposing  water  and  liberating 
a  corresponding  quantity  of  oxygen — 78  (more  correctly  7816)  grains  of 
green  sulphate  of  iron  are  dissolved  in  about  two  ounces  of  water,  and  acidu- 
lated by  a  few  drops  of  sulphuric  or  hydrochloric  acid ;  this  quantity  will 
require  for  peroxidation  10  grains  of  chlorine.  Fifty  grains  of  the  chloride 
of  lime  to  be  examined  are  next  rubbed  up  with  a  little  tepid  water,  and  the 
whole  transferred  to  the  alkalimeter '  before  described,  which  is  then  filled 
up  to  0  with  water,  after  which  the  contents  are  well  mixed  by  agitation. 
The  liquid  is  next  gradually  poured  into  the  solution  of  iron,  with  constant 
stirring  until  the  latter  has  become  peroxidized,  which  may  be  known  by  a 
drop  ceasing  to  give  a  deep  blue  precipitate  with  ferricyanide  of  potassium. 
The  number  of  grain-measures  of  the  chloride  solution  employed  may  then 
be  read  off,  since  these  must  contain  10  grains  of  serviceable  chlorine,  the 
quantity  of  the  latter  in  the  50  grains  may  be  easily  reckoned.  Thus,  sup- 
pose 72  such  measures  have  been  taken,  then 

Measures.  Grs.  chlorine.  Measures.  Grs.  chlorine. 

72  :  10  =  100  :  13-89 

The  bleaching-powder  contains,  therefore,  27-78  per  cent." 

Baryta,  strontia,  and  lime  are  thus  distinguished  from  all  other  substances, 
and  from  each  other. 

Caustic  potassa,  when  fi-ee  fropi  carbonate,  and  caustic  ammonia,  occasion 
no  precipitates  in  dilute  solutions  of  the  earths,  especially  of  the  first  two, 
the  hydrates  being  soluble  in  water. 

•  Vide  p.  227.  "  Graham's  ElementH,  vol.  i.  p.  414. 


MAGNESIUM,  245  '" 

x\lkaline  carbonates,  and  carbonate  of  ampaonia,  give  white  precipitates, 
/nsoluble  in  excess  of  the  precipitant,  with  all  three. 

Sulphuric  acid,  or  a  sulphate,  added  to  very  dilate  solutions  of  the  earths 
in  question,  gives  an  immediate  white  precipitate  with  baryta,  a  similar  pre- 
cipitate after  a  short  interval  with  strontia,  and  occasions  no  change  with 
the  lime-salt.  The  precipitates  with  baryta  and  strontia  are  quite  insoluble 
in  nitric  acid. 

Solution  of  sulphate  of  lime  gives  an  instantaneous  cloud  with  baryta, 
and  one  with  strontia  after  a  little  time.  Sulphate  of  strontia  is  itself  sufl&- 
ciently  soluble  to  occasion  turbidity  when  mixed  with  chloride  of  barium. 

Lastly,  the  soluble  oxalates  give  a  white  precipitate  in  the  most  dilute  so- 
lutions of  lime,  which  is  not  dissolved  by  a  drop  or  two  of  hydrochloric  nor 
by  an  excess  of  acetic  acid.     This  is  an  exceedingly  characteristic  test. 

The  chlorides  of  strontium  and  calcium  dissolved  in  alcohol  colour  the 
flame  of  the  latter  red  or  puj'ple ;  salts  of  baryta  communicate  to  the  flame 
a  pale  green  tint. 

MAGNESIUM. 

A  few  pellets  of  sodium  are  placed  at  the  bottom  of  a  test-tube  of  hard 
German  glass,  and  covered  with  fragments  of  fused  chloride  of  magnesium, 
the  heat  of  a  spirit-lamp  is  then  applied  until  reaction  has  been  induced ; 
this  takes  place  with  great  violence  and  elevation  of  temperature,  chloride 
of  sodium  being  formed,  and  metallic  magnesium  set  free.  When  the  tube 
and  its  contents  are  completely  cold,  it  is  broken  up,  and  the  fragments  put 
into  cold  water,  by  which  the  metal  is  separated  from  the  salt. 

Magnesium  is  a  white,  malleable  metal,  fusible  at  a  red-heat,  and  not  sen- 
sibly acted  upon  by  cold  water ;  it  is  oxidized  by  hot  water.  Heated  in  the 
air,  it  burns  and  produces  magnesia,  which  is  the  only  oxide.  Sulphuric 
and  hydrochloric  acids  dissolve  it  readily,  evolving  hydrogen. 

The  equivalent  of  this  metal  is  12,  and  its  symbol  Mg. 

Magnesia  ;  calcined  magnesia  ;  MgO. — This  is  prepared  with  great  ease 
by  exposing  the  magnesia  alba  of  phawnacy  to  a  full  red-heat  in  an  earthen 
or  platinum  crucible.  It  forms  a  soft,  white  powder,  which  slowly  attracts 
moisture  and  carbonic  acid  from  the  air,  and  unites  quietly  with  water  to  a 
hydrate  which  possesses  a  feeble  degree  of  solubility,  requiring  about  5,000 
parts  of  water  at  60°  (15°-oC)  and  36,000  parts  at  212°  (100°C).  The  al- 
kalinity of  magnesia  can  only  be  observed  by  placing  a  small  portion  in  a 
moistened  state  upon  test-paper;  it  neutralizes  acids,  however,  in  the  most 
complete  manner.     It  is  infusible. 

Chloride  of  magnesium,  MgCl. — When  magnesia,  or  its  carbonate,  ia 
dissolved  in  hydrochloric  acid,  there  can  be  no  doubt  respecting  the  simul- 
taneous production  of  chloride  of  magnesium  and  water;  but  when  this  so- 
lution comes  to  be  evaporated  to  dryness,  the  last  portions  of  water  are 
retained  with  such  obstinacy,  that  decomposition  of  the  water  is  brought 
about  by  the  concurring  attractions  of  magnesium  for  oxyge<^  and  of  chlo- 
rine for  hydrogen ;  hydrochloric  acid  is  expelled,  and  magnesia  remains. 
If,  however,  sal-ammoniac  or  chloride  of  potassium  happen  to  be  present,  a 
double  salt  is  produced,  which  is  easily  rendered  anhydrous.  The  best  mode 
of  preparing  the  chloride  is  to  divide  a  quantity  of  hydrochloric  acid  into 
two  equal  portions,  to  neutralize  one  with  magnesia,  and  the  other  with  am- 
monia, or  carbonate  of  ammonia ;  to  mix  these  solntions,  evaporate  them  to 
dryness,  and  then  expose  the  salt  to  a  red-heat  in  a  loosely  covered  porce- 
lain crucible.  Sal-ammoniac  sublimes,  and  chloride  of  magnesium  in  a  fused 
state  remains ;  the  latter  is  poured  out  upon  a  clean  stone,  and  when  cold, 
transferred  to  a  well-stopped  bottle. 

The  chloride  so  obtained  is  white  and  crystalline.     It  is  very  deliquescent 


246  MAGNESIUM. 

and  highly  soluble  in  water,  from  which  it  cannot  again  be  recovered  by 
evaporation,  for  the  reasons  just  mentioned.  When  long  exposed  to  the  air 
in  a  melted  state,  it  is  converted  into  magnesia.     It  is  soluble  in  alcohol. 

Sulphate  of  magnesia  Epsom  salt;  MgOjSOg-f-THO. — This  salt  occurs 
in  sea-water,  and  in  that  of  many  mineral  springs,  and  is  now  manufactured 
in  large  quantities  by  acting  on  magnesian  lime-stone  by  diluted  sulphuric 
acid,  and  separating  the  sulphate  of  magnesia  from  the  greater  part  of  the 
slightly  soluble  sulphate  of  lime  by  the  filter.  The  crystals  are  derived 
from  a  right  rhombic  prism ;  they  are  soluble  in  an  equal  weight  of  water 
at  60°  (15°-5C),  and  in  a  still  smaller  quantity  at  212°  (100°C).  The  salt 
has  a  nauseous  bitter  taste,  and,  like  many  other  neutral  salts,  purgative 
{)roperties.  When  exposed  to  heat,  6  equivalents  of  water  readily  pass  off, 
the  seventh  being  energetically  retained.  Sulphate  of  magnesia  forms  beau- 
tiful double  salts  with  the  sulphates  of  potassa  and  ammonia,  which  contain 
6  equivalents  of  water  of  crystallization. 

Carbonate  of  magnesia. — The  neutral  carbonate,  MgOjCOj,  occurs  native 
in  rhombohedral  crystals,  resembling  those  of  calcareous  spar,  embedded  in 
talc-slate :  a  soft  earthy  variety  is  sometimes  met  with. 

When  magnesia  alba  is  dissolved  in  carbonic  acid  water,  and  the  solution 
left  to  evaporate  spontaneously,  small  prismatic  crystals  are  deposited, 
which  consist  of  carbonate  of  magnesia,  with  3  equivalents  of  water. 

The  magnesia  alba  itself,  although  often  called  carbonate  of  magnesia,  is 
not  so  in  reality ;  it  is  a  compound  of  carbonate  with  hydrate.  It  is  pre  - 
pared  by  mixing  hot  solutions  of  carbonate  of  potassa  or  soda,  and  sulphate 
of  magnesia,  the  latter  being  kept  in  slight  excess,  boiling  the  whole  a  few 
minutes,  during  which  time  much  carbonic  acid  is  disengaged,  and  then  well 
washing  the  precipitate  so  produced.  If  the  solution  be  very  dilute,  the 
magnesia  alba  is  exceedingly  light  and  bulky ;  if  otherwise,  it  is  denser. 
The  composition  of  this  precipitate  is  not  perfectly  constant.  In  most  cases 
it  contains  4(MgO,C02)-f-MgO,HO-i-  6H0. 

Magnesia  alba  is  slightly  soluble  in  water,  especially  when  cold. 

Phosphate  of  magnesia,  2MgO,HO,P05-|- 14H0.  —  This  salt  separates 
in  small  colourless  prismatic  crystals  when  solutions  of  phosphate  of  soda 
and  sulphate  of  magnesia  are  mixed  and  suffered  to  stand  some  time.  Prof. 
Graham  states  that  it  is  soluble  in  about  1,000  parts  of  cold  water,  but 
Berzelius  describes  a  phosphate  which  only  requires  15  parts  of  water  for 
solution :  this  can  hardly  be  the  same  substance.  Phosphate  of  magnesia 
exists  in  the  grain  of  the  cereals,  and  can  be  detected  in  considerable 
quantity  in  beer. 

Phosphate  of  magnesia  and  ammonia,  2MgO,NH40,P05-{-12HO. — When 
a  soluble  phosphate  is  mixed  with  a  salt  of  magnesia,  and  ammonia  or  its 
carbonate  added,  a  crystalline  precipitate,  having  the  above  composition, 
subsides  immediately,  if  the  solutions  are  concentrated,  and  after  some  time 
if  very  dilute ;  in  the  latter  case,  the  precipitation  is  promoted  by  stirring. 
This  salt  is  lightly  soluble  in  pure  water,  but  scarcely  so  in  saline  liquids. 
When  heated,  it  is  resolved  into  bibasic  phosphate  (pyrophosphate)  of  mag- 
nesia, containing  35-71  per  cent,  of  magnesia.  At  a  strong  red-heat  it  fuses 
to  a  white  enamel-like  mass.  The  phosphate  of  magnesia  and  ammonia 
sometimes  forms  an  urinary  calculus. 

In  practical  analysis,  magnesia  is  often  separated  from  solutions  by 
bringing  it  into  this  state.  The  liquid,  free  from  alumina,  lime,  &c.,  is 
mixed  with  phosphate  of  soda  and  excess  of  ammonia,  and  gently  heated 
tor  a  short  time.  The  precipitate  is  collected  upon  a  filter  and  thoroughly 
washed  with  water  containing  a  little  sal-ammoniac,  after  which  it  is  dried, 
ignited  to  redness  and  weighed.  The  proportion  of  magnesia  is  then  easily 
calculated. 


MAGNEBIUM.  247 

Silicates  of  magnesia. — The  following  natural  compounds  belong  to  thia 
class : — Steatite  or  aoap-stcne,  MgO,Si03,  a  soft,  white,  or  pale-coloured,  amor- 
phous substance,  found  iu  Cornwall  and  elsewhere ;  Meerschaum,  MgOjSiOg-l- 
HO,  from  which  pipe-bowls  are  often  manufactured  ; — Chrysolite,  3MgO,Si03, 
a  crystallized  mineral,  sometimes  employed  for  ornamental  purposes  ;  a  por- 
tion of  magnesia  is  commonly  replaced  by  protoxide  of  iron  which  communi- 
cates a  green  colour ; — Serpentine  is  a  combination  of  silicate  and  hydrate  of 
magnesia ; — Jade,  an  exceedingly  hard  stone,  brought  from  New  Zealand,  con- 
tains silicate  of  magnesia  combined  with  silicate  of  alumina ;  its  green 
colour  is  due  to  sesquioxide  of  chromium ;  —  Augite  and  hornblende  are 
essentially  double  salts  of  silicic  acid,  magnesia,  and  lime,  in  which  the 
magnesia  is  more  or  less  replaced  by  its  isomorphous  substitute,  protoxide 
of  iron. 


The  salts  of  magnesia  are  strictly  isomorphous  with  those  of  the  protox- 
ides of  zinc,  of  iron,  of  copper,  &c. ;  they  are  usually  colourless,  and  are 
easily  recognised  by  the  following  characters :  — 

A  gelatinous  white  precipitate  with  caustic  alkalis,  including  ammonia, 
insoluble  in  excess,  but  soluble  in  solution  of  sal-ammoniac. 

A  white  precipitate  with  the  carbonates  of  potassa  and  soda,  but  none 
with  carbonate  of  ammonia  in  the  cold. 

A  white  crystalline  precipitate  with  soluble  phosphates,  on  the  addition 
of  a  little  ammonia. 


248  ALUxMINIUM. 


SECTION    III. 
METALS   OF    THE    EARTHS    PROPER. 


ALUMINUM    OR   ALUMINIUM. 


Alumina,  the  only  known  oxide  of  this  metal,  is  a  substance  of  very  abun- 
dant occurrence  in  nature  in  the  state  of  silicate,  as  in  felspar  and  its  asso- 
ciated minerals,  and  in  the  various  modifications  of  clay  thence  derived. ' 
Aluminium  is  prepared  in  the  same  manner  as  magnesium,  but  with  rather 
more  difficulty ;  a  platinum  or  iron  tube  closed  at  one  extremity  may  be  em- 
ployed. Sesquichloride  of  aluminium  is  first  introduced,  and  upon  that 
about  an  equal  bulk  of  potassium  loosely  wrapped  in  platinum  foil.  The 
lower  part  of  the  tube  is  then  heated  so  as  to  sublime  the  chloride  and  bring 
its  vapours  in  contact  with  the  melted  potassium.  The  reduction  takes  place 
with  great  disengagement  of  heat.  The  metal,  separated  by  cold  water  from 
the  alkaline  chloride,  has  a  tin- white  colour  and  perfect  lustre.  It  is  ob- 
tained in  small  fused  globules  by  the  heat  of  reduction,  which  are  malleabk , 
and  have  a  specific  gravity  of  2-6.  When  heated  in  the  air  or  in  oxygen,  it 
takes  fire  and  burns  with  brilliancy,  producing  alumina. 

Aluminium  has  for  its  equivalent  the  number  13-7;  its  symbol  is  Al. 

Alumina,  ALOg. — This  substance  is  inferred  to  be  a  sesquioxide,  from  its 
isomorphism  with  the  red  oxide  of  iron.  It  is  prepared  by  mixing  solution 
of  alum  with  excess  of  ammonia,  by  which  an  extremely  bulky,  white,  gela- 
tinous precipitate  of  hydrate  of  alumina  is  thrown  down.  This  is  washed, 
dried,  and  ignited  to  whiteness.  Thus  obtained,  alumina  constitutes  a  white, 
tasteless,  coherent  mass,  very  little  acted  upon  by  acids.  The  hydrate,  on 
the  contrary,  when  simply  dried  in  the  air,  or  by  gentle  heat,  dissolves  freely 
in  dilute  acid,  and  in  caustic  potassa  or  soda,  from  which  it  is  precipitated 
by  the  addition  of  sal-ammoniac.  Alumina  is  fusible  before  the  oxyhydro- 
gen  blowpipe.  The  mineral  called  corundum,  of  which  the  ruby  and  sap- 
phire are  transparent  varieties,  consists  of  nearly  pure  alumina  in  a  crystal- 
lized state,  with  a  little  colouring  oxide  ;  emery,  used  for  polishing  glass  and 
metals,  is  a  coarse  variety  of  corundum.  Alumina  is  a  very  feeble  base, 
and  its  salts  have  often  an  acid  reaction. 

Sesquichloride  of  aluminium,  AlgClg. — The  solution  of  alumina  in  hydro- 
chloric acid  behaves,  when  evaporated  to  dryness,  like  that  of  magnesia,  the 
chloride  being  decomposed  by  the  water,  and  alumina  and  hydrochloric  acid 
produced.  The  chloride  may  be  thus  prepared : — Pure  precipitated  alumina 
is  dried  and  mixed  with  lampblack,  and  the  mixture  strongly  calcined  in  a 
covered  crucible.  It  is  then  transferred  to  a  porcelain  tube  fixed  across  a 
furnace,  and  heated  to  redness  in  a  stream  of  chlorine  gas,  when  the  alu- 
mina, yielding  to  the  attraction  of  the  chlorine  on  the  one  hand,  and  the 
carbon  on  the  othei-,  for  each  of  its  constituents,  suffers  decomposition,  car- 
bonic oxide  being  disengaged,  and  sesquichloride  of  aluminium  formed ;  the 
latter  sublimes,  and  condenses  in  the  cool  part  of  the  tube. 


ALUMINIUM.  249 

Sesquichloride  of  aluminium  is  a  crystalline  yellowish  substance,  exces- 
sively greedy  of  moisture,  and  very  soluble.  Once  dissolved,  it  cannot  be 
again  recovered.  It  is  said  to  combine  with  sulphuretted  and  phosphoretted 
hydrogen,  and  with  ammonia. 

Sulphate  of  alumina,  AlgOgjSSOj-j-l^HO. — Prepared  by  saturating 
dilute  sulphuric  acid  with  hydrate  of  alumina,  and  evaporating.  It  crystal- 
lizes in  thin,  pearly  plates,  soluble  in  2  parts  of  water ;  it  has  a  sweet  and 
astringent  taste,  and  an  acid  reaction.  Heated  to  redness,  it  is  decomposed, 
leaving  pure  alumina.  Two  other  sulphates  of  alumina,  with  excess  of  base, 
are  also  described,  one  of  which  is  insoluble  in  water. 

Sulphate  of  alumina  combines  with  the  sulphates  of  potassa,  soda,  and 
ammonia,  forming  double  salts  of  great  interest,  the  alums.  Common  alum, 
the  source  of  all  the  preparations  of  alumina,  contains  Al203,3SOj-fKO,SO, 
-J-24HO.  It  is  manufactured,  on  a  very  large  scale,  from  a  kind  of  slaty  clay, 
loaded  with  bisulphide  of  iron,  which  abounds  in  certain  parts.  This  is 
gently  roasted,  and  then  exposed  to  the  air  in  a  moistened  state ;  oxygen  ia 
absorbed,  the  sulphur  becomes  acidified,  sulphate  of  protoxide  of  iron  and 
sulphate  of  alumina  are  produced,  and  afterwards  separated  by  lixiviation 
with  water.  The  solution  is  next  concentrated,  and  mixed  with  a  quantity 
of  chloride  of  potassium,  which  decomposes  the  iron-salt,  forming  proto- 
chloride  of  iron  and  sulphate  of  potassa,  which  latter  combines,  with  the 
sulphate  of  alumina,  to  alum.  By  crystallization,  the  alum  is  separated 
from  the  highly  soluble  chloride  of  iron,  and  afterwards  easily  purified  by  a 
repetition  of  that  process.  Other  methods  of  alum-making  exist,  and  are 
sometimes  employed.  Potassa-alum  crystallizes  in  colourless,  transparent 
octahedrons,  which  often  exhibit  the  faces  of  the  cube.  It  has  a  sweetish 
and  astringent  taste,  reddens  litmus  paper,  and  dissolves  in  18  parts  of  water 
at  60°  (15° -50,  and  in  its  own  weight  of  boiling  water.  Exposed  to  heat, 
it  is  easily  rendered  anhydrous,  and,  by  a  very  high  temperature,  decom- 
posed. The  crystals  have  little  tendency  to  change  in  the  air.  Alum  ia 
largely  used  in  the  arts,  in  prepai'ing  skins,  dyeing,  &c. ;  it  is  occasionally 
contaminated  with  oxide  of  iron,  which  interferes  with  some  of  its  applica- 
tions. The  celebrated  Roman  alum,  made  from  alum-stone,  a  felspathic  rock, 
altered  by  sulphurous  vapours,  was  once  much  prized  on  account  of  its  free- 
dom from  this  impurity. 

A  mixture  of  dried  alum  and  sugar,  carbonized  in  an  open  pan,  and  then 
heated  to  redness,  out  of  contact  of  air,  furnishes  the  pyrojjhorus  of  Homberg, 
which  ignites  spontaneously  on  exposure  to  the  atmosphere.  The  essential 
ingredient  is,  in  all  probability,  finely  divided  sulphide  of  potassium. 

Soda-alum,  in  which  sulphate  of  soda  replaces  sulphate  of  potassa,  has  a 
form  and  constitution  similar  to  that  of  the  salt  described ;  it  is,  however, 
much  more  soluble,  and  difficult  to  crystallize. 

Ammonia-alum,  containing  NH^OjSOg,  instead  of  KOjSOg,  very  closdy  re- 
sembles common  potassa-alum,  having  the  same  figure,  and  appearance,  and 
constitution,  and  nearly  the  same  degree  of  solubility  as  that  substance  It 
is  sometimes  manufactured  for  commercial  use.  When  heated  to  redness,  it 
yields  pure  alumina. 

Few  of  the  other  salts  of  alumina,  except  the  silicates,  present  points  of 
interest ;  these  latter  are  of  great  importance.  Silicates  of  alumina  entei 
into  the  composition  of  a  number  of  crystallized  minerals,  among  which 
felspar  occupies,  by  reason  of  its  abundant  occurrence,  a  prominent  place 
Granite,  porphyry,  trachyte,  and  other  ancient  unstratified  rocks,  consist  in 
great  part  of  this  mineral,  which,  under  peculiar  circumstances,  by  no  means 
well  understood,  and  particularly  by  the  action  of  the  carbonic  acid  of  the 
air,  suflfers  complete  decomposition,  becoming  converted  into  a  soft,  friable 
mass  of  earthy  matter.     This  is  the  origin  of  clay ;  the  change  itself  U  seen 


250  BERYLLIUM. 

in  great  perfection  in  certain  districts  of  Devonshire  and  Cornwall,  the  felspar 
of  the  fine  white  granite  of  those  localities  being  often  disintegrated  to  an 
extraordinary  depth,  and  the  rock  altered  to  a  substance  resembling  soft 
mortar.  By  washing,  this  finely  divided  matter  is  separated  from  the  quartz 
and  mica,  and  the  milk-like  liquid,  being  collected  in  tanks  and  sufi'ered  to 
stand,  deposits  the  suspended  clay,  which  is  afterwards  dried,  first  in  the 
air  and  afterwards  in  a  stove,  and  employed  in  the  manufacture  of  porcelain. 
The  composition  assigned  to  unaltered  felspar  is  AlgOg,  SSiOg-f-KO.SiOg,  or 
alum,  having  silicic  acid  in  the  place  of  sulphuric.  The  exact  nature  of  the 
change  by  which  it  passes  into  porcelain  clay  is  unknown,  although  it  evi- 
dently consists  in  the  abstraction  of  silica  and  alkali.' 

When  the  decomposing  rock  contains  oxide  of  iron,  the  clay  produced  is 
coloured.  The  difi"erent  varieties  of  shale  and  slate  result  from  the  alteration 
of  ancient  clay-beds,  apparently  in  many  instances  by  the  infiltration  of  water 
holding  silica  in  solution ;  the  dark  appearance  of  some  of  these  deposits  is 
due  to  bituminous  matter. 

It  is  a  common  mistake  to  confound  clay  with  alumina ;  all  clays  are  es- 
sentially silicates  of  that  base  ;  they  often  vary  a  good  deal  in  composition. 
Dilute  acids  exert  little  action  on  these  compounds ;  but  by  boiling  with  oil 
of  vitriol,  alumina  is  dissolved  out,  and  finely  divided  silica  left  behind. 
Clays  containing  an  admixture  of  carbonate  of  lime  are  termed  marls,  and 
are  recognized  by  effervescing  with  acids. 

A  basic  silicate  of  alumina,  SAlgOg,  SiOg,  is  found  crystallized,  constituting 
the  beautiful  mineral  called  cyanite.  The  compounds  formed  by  the  union 
of  the  silicates  of  alumina  with  other  silicates  are  almost  innumerable  ;  a 
soda-felspar,  albile,  containing  that  alkali  in  place  of  potassa,  is  known,  and 
there  are  two  somewhat  similar  lithia-compounds  spodumene  and  petalite. 
The  zeolites  belong  to  this  class:  analcime,  nepheline,  mesotype,  &c.,  are  double 
silicates  of  soda  and  alumina,  with  water  of  crystallization.  Slilbite,  heulan- 
dite,  laumonite,  prehnite,  &c.,  consist  of  silicate  of  lime,  combined  with  silicate 
of  alumina.  The  garnets,  axinite,  mica,  &c.,  have  a  similar  composition,  but 
are  anhydrous.  Sesquioxide  of  iron  is  very  often  substituted  for  alumina 
in  these  minerals. 


Alumina,  when  in  solution,  is  distinguished  without  difficulty. 

Caustic  potassa  and  soda  occasion  white  gelatinous  precipitates  of  hydrate 
of  alumina,  freely  soluble  in  excess  of  the  alkali. 

Ammonia  produces  a  similar  precipitate,  insoluble  in  excess  of  the  reagent. 

The  alkaline  carbonates  and  carbonate  of  ammonia  precipitate  the  hydrate, 
with  escape  of  carbonic  acid.     The  precipitates  are  insoluble  in  excess. 

BERYI-LIUM  (GLUCINUM). 

This  metal  is  prepared  from  the  chloride  in  the  same  manner  as  aluminium, 
it  is  fusible  with  great  difficulty,  not  acted  upon  by  cold  water  and  burns 
.vhen  heated  in  the  air,  producing  berylla. 

The  equivalent  of  beryllium  is  6-9,  and  the  symbol  Be. 

'  A  specimen  of  white  porcelain  clay  from  Dartmoor,  Devon,  gave  the  author  the  following 
result  on  analysis  : — 

Silica 47-20 

Alumina,  with  trace  of  iron  and  manganese 38-80 

Lime  0-24 

Water  12-00 

Alkali  and  loss 1-76 

100-00 


CERIUM,     LANTHANIUM,     AND     DIDYMIUM        251 

Berylla,  BcjOg,  is  a  rare  earth  found  in  the  emerald,  beryl,  and  euclasCy 
from  which  it  may  be  extracted  by  a  tolerably  simple  process.  It  very  much 
resembles  alumina,  but  is  distinguished  from  that  substance  by  its  solubility, 
when  freshly  precipitated,  in  a  cold  solution  of  carbonate  of  ammonia,  from 
which  it  is  again  thrown  down  on  boifing.  The  salts  of  berylla  have  a  sweet 
taste,  whence  its  former  name  glucina  {yXvKvs)' 

YTTRIUM. 

The  metal  of  a  very  rare  earth,  yttria,  contained  in  a  few  scarce  minerals 
The  name  is  derived  from  Ytterby,  a  place  in  Sweden,  where  one  of  these, 
gadolinite,  is  found.  It  is  obtained  from  the  chloride  by  the  process  alreadj 
described ;  it  resembles  in  character  the  preceding  metal. 

Ordinary  yttria  is  stated  by  Professor  Mosander  to  be  a  mixture  of  the 
oxides  of  not  less  than  three  metals,  namely,  Yttrium,  erbium,  and  terbium^ 
which  differ  in  the  characters  of  their  salts,  and  in  other  particulars.  The 
first  is  a  very  powerful  base,  the  two  others  are  weak  ones.  They  are 
separated  with  extreme  difficulty. 

CERIUM,    LANTHANIUM,    AND    DIDYMIUM. 

The  oxides  of  these  very  rare  metals  are  found  associated  in  the  Swedish 
mineral  cerite ;  the  equivalent  of  cerium  is  about  47,  and  its  symbol  Ce. 
This  metal  foi-ms  a  protoxide  CeO,  and  a  sesquioxide  CejOg. 

The  crude  sesquioxide  of  cerium  obtained  by  precipitating  the  double 
sulphate  of  cerium  and  potassa  directly  derived  from  cerite  by  carbonate  of 
potassa,  has  been  shown  by  Mosander  to  contain  in  addition  to  sesquioxide 
of  cerium,  the  oxides  of  two  other  metals,  to  which  the  above  names  were 
given.  After  ignition  it  is  red-brown.  The  complete  separation  of  these 
three  bodies  is  attended  with  the  greatest  difficulty,  and  has  indeed  been 
only  partially  accomplished.*  Oxide  of  cerium  may  be  obtained  pure  by 
heating  the  mixture  of  the  three  oxides  first  with  diluted  and  afterwards 
with  concentrated  nitric  acid,  which  gradually  removes  the  whole  of  the 
oxides  of  lathanium  and  didymium. 

The  yellow  oxide  of  cerium,  obtained  by  igniting  the  nitrate,  is  a  mixture 
of  proto-  and  sesquioxide,  which  are  extremely  difficult  to  obtain  in  a  sepa- 
rate state.  The  salts  of  the  former  are  colourless,  and  are  completely  pre- 
cipitated by  sulphate  of  potassa ;  the  sulphate  of  the  sesquioxide  is  yellow, 
and  forms  a  beautiful  double  salt  with  sulphate  of  potassa,  which  is  decom- 
posed by  water.  The  metal  cerium  has  been  obtained  from  the  chloride  by 
the  action  of  sodium. 

Oxide  of  lanthanium,  as  pure  as  it  has  been  obtained,  forms  a  very  pale 
salmon-coloured  powder,  unchanged  by  ignition  in  open  or  close  vessels.  In 
contact  with  water  it  gives  a  snow-white  bulky  hydrate  which  has  an  alkaline 
reaction,  and  decomposes  ammoniacal  salts  by  boiling.  Its  salts  are 
crystallizable,  colourless,  sweet,  and  astringent,  and  are  precipitated  by 
sulphate  of  potassa. 

A  tolerably  pure  lanthanium-salt  may  be  obtained  by  slowly  crystallizing 
an  acid  solution  containing  the  sulphates  of  lanthanium  and  didymium, 
picking  out  the  rose-coloured  crystals  (containing  didymium),  and  the  viole* 
ones  (containing  lanthanium  and  didymium),  adding  the  solution  of  the  lattei 
to  the  mother-liquor,  and  repeating  the  process.  In  this  manner  the  whole 
of  the  didpnium-salt  may  be  finally  separated  by  crystallization.  Metallic 
lanthanium  is  prepared  like  cerium. 

The  occasional  brown  colour  of  crude  oxide  of  cerium  is  due  to  oxide  of 

*  A  synopsis  of  the  various  methods  for  the  separation  of  cerium,  lanthanium,  and  didy 
mium  has  been  given  by  Mr.  H.  Watts.    Chem.  Sec.  Quar.  Jour.  ii.  140. 


252  ZIRCONIUM  —  THORIUM  —  GLASS. 

didymium.  In  a  pure  state,  it  forms  a  brown  powder,  soluble  in  acids,  and 
generating  a  series  of  red  crystallizable  salts,  from  which  caustic  potassa 
precipitates  a  violet-  blue  hydrate,  quickly  changing  by  exposure  to  the  air. 
It  communicates  to  glass  an  amethystine  colour.' 

ZIRCONIUM. 

Prepared  by  heating  the  double  fluoride  of  zirconium  and  potassium  with 
potassium,  and  separating  the  salt  with  cold  water.  The  metal  is  black, 
and  acquires  a  feeble  lustre  when  burnished.  It  takes  fire  when  heated  iu 
the  air. 

The  equivalent  of  zirconium  is  33-6,  and  its  symbol  Zr. 

ZiRCONiA,  ZrgOg,  is  a  rare  earth,  very  closely  resembling  alumina,  found 
together  with  silica,  in  the  mineral  zircon.  The  salts  are  colourless  and  have 
an  astringent  taste. 

Svanberg  has  rendered  it  probable  that  an  undescribed  metallic  oxide 
exists  in  certain  varieties  of  zircon,  for  the  metal  of  which  he  proposes  the 
name  of  norium. 

THOBIUM. 

The  metal  of  an  earth  from  a  very  rare  mineral,  thorite ;  it  agrees  in 
character  with  aluminium,  and  is  obtained  by  similar  means. 

The  equivalent  of  thorium  is  59-6,  and  its  symbol  Th. 

Thoria,  ThO,  is  remarkable  for  its  great  specific  gravity,  and  is  otherwise 
distinguished  by  peculiar  properties  which  separate  it  from  all  other 
substances. 

Manufacture  of  Glass,  Porcelain,  and  Earthenware. 

Glass. — Glass  is  a  mixture  of  various  insoluble  silicates,  with  excess  of 
silica,  altogether  destitute  of  crystalline  structure :  the  simple  silicates,  formed 
by  fusing  the  bases  with  silicic  acid  in  equivalent  proportions,  very  often 
crystallize,  which  happens  also  with  the  greater  number  of  the  natural  sili- 
cates included  among  the  earthly  minerals.  Compounds  identical  with  some 
of  these  are  also  occasionally  formed  in  artificial  processses,  where  large 
masses  of  melted  glassy  matter  are  suJBFered  to  cool  slowly.  The  alkaline 
silicates,  when  in  a  state  of  fusion,  have  the  power  of  dissolving  a  large 
quantity  of  silica. 

Two  principal  varieties  of  glass  are  met  with  in  commerce,  naiftely,  glass 
composed  of  silica,  alkali,  and  lime,  and  glass  containing  a  large  proportion 
of  silicate  of  lead ;  crown  and  plate-glass  belong  to  the  former  division ;  flint- 
glass,  and  the  material  of  artificial  gems  to  the  latter.  The  lead  promotes 
fusibility,  and  confers  also  density  and  lustre.  Common  green  bottle  glass 
contains  no  lead,  but  much  silicate  of  black  oxide  of  iron,  derived  from  the 
impure  materials.  The  principle  of  the  glass  manufacture  is  very  simple. 
Silica,  in  the  shape  of  sand,  is  heated  with  carbonate  of  potassa  or  soda, 
and  slaked  lime  or  oxide  of  lead ;  at  a  high  temperature,  fusion  and  combi- 
nation occur,  and  the  carbonic  acid  is  expelled.  When  the  melted  mass  has 
become  perfectly  clear  and  free  from  air-bubbles,  it  is  left  to  cool  until  it  as- 
sumes the  peculiar  tenacious  condition  proper  for  working. 

The  operation  of  fusion  is  conducted  in  large  crucibles  of  refractory  fire- 
clay, which  in  the  case  of  lead-glass  are  covered  by  a  dome  at  the  top,  and 
have  an  opening  at  the  side  by  which  the  materials  are  introduced  and  the 
melted  glass  withdrawn.  Great  care  is  exercised  in  the  choice  of  the  sand, 
which  must  be  quite  white  and  free  from  oxide  of  iron.  Red-lead,  one  of 
the  higher  oxides,  is  preferred  to  litharge,  although  immediately  reduced  to 

*  Annalen  der  Chemie  und  Pharmacie,  xlvlii.  210. 


GLASS.  253 

protoxide  by  the  heat,  the  liberated  oxygen  serving  to  destroy  any  combus- 
tible matter  which  might  accidentally  find  its  way  into  the  crucible  and  stain 
the  glass  by  reducing  a  portion  of  the  lead.  Potassa  gives  a  better  glass 
than  soda,  although  the  latter  is  very  generally  employed,  from  its  lower 
price,  A  certain  proportion  of  broken  and  waste  glass  of  the  same  kind  is 
always  added  to  the  other  materials. 

Articles  of  blown  glass  are  thus  made : — The  workman  begins  by  collect- 
ing a  proper  quantity  of  soft,  pasty  glass  at  the  end  of  his  blow-pipe,  an 
iron  tube,  five  or  six  feet  in  length,  terminated  by  a  mouth-piece  of  wood  ; 
he  then  commences  blowing,  by  which  the  lump  is  expanded  into  a  kind  of 
flask,  susceptible  of  having  its  form  modified  by  the  position  in  which  it  is 
held,  and  the  velocity  of  rotation  continually  given  to  the  iron  tube.  If  an 
open-mouthed  vessel  is  to  be  made,  an  iron  rod,  called  a  pontil  or  puntil,  is 
dipped  into  the  glass-pot  and  applied  to  the  bottom  of  the  flask,  to  which  it 
thus  serves  as  a  handle,  the  blowpipe  being  removed  by  the  application  of  a 
cold  iron  to  the  neck.  The  vessel  is  then  re-heated  at  a  hole  left  for  the 
purpose  in  the  wall  of  the  furnace,  and  the  aperture  enlarged,  and  the  vessel 
otherwise  altered  in  figure  by  the  aid  of  a  few  simple  tools,  until  completed. 
It  is  then  detached,  and  carried  to  the  annealing  oven,  where  it  undergoes 
slow  and  gradual  cooling  during  many  hours,  the  object  of  which  is  to  obvi- 
ate the  excessive  brittleness  always  exhibited  by  glass  which  has  been 
quickly  cooled.  The  large  circular  tables  of  crown-glass  are  made  by  a  very 
curious  process  of  this  kind;  the  globular  flask  at  first  produced,  trans- 
ferred from  the  blowpipe  to  the  pontil,  is  suddenly  made  to  assume  the  form 
of  a  flat  disc  by  the  centrifugal  force  of  the  rapid  rotatory  movement  given 
to  the  rod.  Plate-glass  is  cast  upon  a  flat  metal  table,  and  after  very  care- 
ful annealing,  ground  true  and  polished  by  suitable  machinery.  Tubes  arc 
made  by  rapidly  drawing  out  a  hollow  cylinder ;  and  from  these  a  great  va- 
riety of  useful  apparatus  may  be  constructed  with  the  help  of  a  lamp  and 
blowpipe,  or  still  better,  the  bellows-table  of  the  barometer-maker.  Small 
tubes  may  be  bent  in  the  flame  of  a  spirit-lamp  or  gas-jet,  and  cut  with 
great  ease  by  a  file,  a  scratch  being  made,  and  the  two  portions  pulled  or 
broken  asunder  in  a  way  easily  learned  by  a  few  trials. 

Specimens  of  the  two  chief  varieties  of  glass  gave  the  following  results 
on  analysis : — 


Bohemian  plate-glass  (excellent).* 

Silica  60-0 

Potassa 250 

Lime  12*5 

97-5 


English  flintrglass.* 

Silica 51-93 

Potassa 13-77 

Oxide  of  lead 33-28 


98-98 


The  diflBcultly-fusible  white  Bohemian  tube,  so  invaluable  in  organic  che- 
mistry, has  been  found  to  contain  in  100  parts : — 

Silica 72-80 

Lime,  with  trace  of  alumina 9-68 

Magnesia '40 

Potassa 16-80 

Traces  of  manganese,  &c.,  and  loss -32 

Different  colours  are  often  communicated  to  glass  by  metallic  oxides. 
Thus,  oxide  of  cobalt  gives  deep  blue ;  oxide  of  manganese,  amethyst ;  sub- 
oxide of  copper,  ruby-red;  black  oxide  of  copper,  green;  the  oxides  of 
iron,  dull  green  or  brown,  &c.     These  are  either  added  to  the  melted  con 


*  Mitscherlich,  L«hrbuch,  ii.  187  ■  FaracUy. 

22 


..*_v4i>.*. 


254  PORCELAIN    AND    EARTHENWARE. 

tents  of  the  glass-pot,  in  which  they  dissolve,  or  applied  in  a  particular 
manner  to  the  surface  of  the  plate  or  other  object,  which  is  then  re-heated 
until  fusion  of  the  colouring  matter  occurs ;  such  is  the  practice  of  enam- 
elling and  glass-painting.  An  opaque  white  appearance  is  given  by  oxide 
of  tin ;  the  enamel  of  watch-faces  is  thus  prepared. 

When  silica  is  melted  with  twice  its  weight  of  carbonate  of  potassa  or 
soda,  and  the  product  treated  with  water,  the  greater  part  dissolves,  yielding 
a  solution  from  which  acids  precipitate  gelatinous  silica.  This  is  the  soluble 
glass  sometimes  mentioned  by  chemical  writers ;  its  solution  has  been  used 
for  rendering  muslin  and  other  fabrics  of  cotton  or  linen  less  combustible. 

Porcelain  and  earthenware.  —  The  plasticity  of  natural  clays,  and  their 
hardening  when  exposed  to  heat,  are  properties  which  suggested  in  very  early 
times  their  application  to  the  making  of  vessels  for  the  various  purposes  of 
daily  life ;  there  are  few  branches  of  industry  of  higher  antiquity  than  that 
exercised  by  the  potter. 

True  porcelain  is  distinguished  from  earthenware  by  very  obvious  charac- 
ters. In  porcelain  the  body  of  the  ware  is  very  compact  and  translucent, 
and  breaks  with  a  conchoidal  fracture,  symptomatic  of  a  commencement  of 
fusion.  The  glaze,  too,  applied  for  giving  a  perfectly  smooth  surface,  is 
closely  adherent,  and  in  fact  graduates  by  insensible  degrees  into  the  sub- 
stance of  the  body.  In  earthenware,  on  the  contrary,  the  fracture  is  open 
and  earthy,  and  the  glaze  detachable  with  greater  or  less  facility.  The  com- 
pact and  partly  glassy  character  of  porcelain  is  the  result  of  the  admixture 
with  the  clay  of  a  small  portion  of  some  substance,  fusible  at  the  temperature 
to  which  the  ware  is  exposed  when  baked  or  fired,  and  which,  absorbed  by 
the  more  infusible  portion,  binds  the  whole  into  a  solid  mass  on  cooling ; 
such  substances  are  found  in  felspar,  and  in  a  small  admixture  of  silicate 
of  lime,  or  alkali.  The  clay  employed  in  porcelain-making  is  always 
directly  derived  from  the  decomposed  felspar,  none  of  the  clays  of  the  secon- 
dary strata  being  pure  enough  for  the  purpose ;  it  must  be  white,  and  free 
from  oxide  of  iron.  To  diminish  the  retraction  which  this  substance  under- 
goes in  the  fire,  a  qantity  of  finely  divided  silica,  carefully  prepared  by 
crushing  and  grinding  calcined  flints  or  chert,  is  added,  together  with  a 
proper  proportion  of  felspar  or  other  fusible  material,  also  reduced  to  impal- 
pable powder.  The  utmost  pains  are  taken  to  effect  perfect  uniformity  of 
mixture,  and  to  avoid  the  introduction  of  particles  of  grit  or  other  foreign 
bodies.  The  ware  itself  is  fashioned  either  on  the  potter's  wheel ; — a  kind 
of  vertical  lathe; — or  in  moulds  of  plaster  of  Paris,  and  dried,  first  in  the  air, 
afterwards  by  artificial  heat,"  and  at  length  completely  hardened  by  exposure 
to  the  temperature  of  ignition.  The  porous  biscuit  is  now  fit  to  receive  its 
glaze,  which  may  be  either  ground  felspar,  or  a  mixture  of  gypsum,  silica, 
and  a  little  porcelain  clay,  diffused  through  water.  The  piece  is  dipped  for 
a  moment  into  this  mixture,  and  withdrawn ;  the  water  sinks  into  its  sub- 
stance, and  the  powder  remains  evenly  spread  upon  its  surface ;  it  is  once 
more  dried,  and  lastly,  fired  at  an  exceedingly  high  temperature. 

The  porcelain-furnace  is  a  circular  structure  of  masonry,  having  several 
fire-places,  and  surmounted  by  a  lofty  dome.  Dry  wood  or  coal  is  consumed 
ah  fuel,  and  its  flame  directed  into  the  interior,  and  made  to  circulate  around 
and  among  the  earthen  cases,  or  seggars  in  which  the  articles  to  be  fired  are 
packed.  Many  hours  are  required  for  this  operation,  which  must  be  very 
carefully  managed.  After  the  lapse  of  several  days,  when  the  fui'nace  has 
completely  cooled,  the  contents  are  removed  in  a  finished  state,  so  far  as 
regards  the  ware. 

The  ornamental  part,  consisting  of  gilding  and  painting  in  enamel,  has  yet 
to  be  executed,  after  which  the  pieces  are  again  heated,  in  order  to  flux  the 
colours      This  operation  has  sometimes  to  be  repeated  more  than  once. 


EARTHENWARE.  255 

The  mamifacture  of  porccTain  in  Europe  is  of  modern  origin  ;  the  Chinese 
have  possessed  the  art  from  the  commencement  of  the  seventh  century,  and 
their  ware  is,  in  some  respects,  altogether  unequalled.  The  materials  em- 
ployed by  them  are  known  to  be  kaolin,  or  decomposed  felspar ;  petunlze,  or 
quartz  reduced  to  fine  powder ;  and  the  ashes  of  fern,  which  contain  carbonate 
of  potassa. 

Stoneware.  —  This  is  a  coarse  kind  of  porcelain,  made  from  clay  containing 
oxide  of  iron  and  a  little  lime,  to  which  it  owes  its  partial  fusibility.  The  gla- 
zing is  performed  by  throwing  common  salt  into  the  heated  furnace ;  this  is  vo- 
latilized, and  decomposed  by  the  joint  agency  of  the  silica  of  the  ware,  and 
of  the  vapour  of  water  always  present ;  hydrochloric  acid  and  soda  are  pro- 
duced, the  latter  forming  a  silicate,  which  fuses  over  the  surface  of  the  ware, 
and  gives  a  thin,  but  excellent  glaze. 

Earthenware.  —  The  finest  kind  of  earthenware  is  made  from  a  white 
secondary  clay,  mixed  with  a  considerable  quantity  of  silica.  The  articles 
are  thoroughly  dried  and  fired,  after  which  they  are  dipped  into  a  readily 
fusible  glaze-mixture,  of  which  oxide  of  lead  is  usually  an  important  ingre- 
dient, and,  when  dry,  re-heated  to  the  point  of  fusion  of  the  latter.  The 
whole  process  is  much  easier  of  execution  than  the  making  of  porcelain,  and 
demands  less  care.  The  ornamental  designs  in  blue  and  other  colours,  so 
common  upon  plates  and  household  articles,  are  printed  upon  paper  in  enamel 
pigment,  mixed  with  oil,  and  transferred,  while  still  wet,  to  the  unglazed 
ware.  When  the  ink  becomes  dry,  the  paper  is  washed  off,  and  the  glazing 
completed. 

The  coarser  kinds  of  earthenware  are  sometimes  covered  with  a  whitish 
opaque  glaze,  which  contains  the  oxides  of  lead  and  tin ;  such  glaze  is  very 
liable  to  be  attacked  by  acids,  and  is  dangerous  for  culinary  vessels. 

Crucibles  when  of  good  quality,  are  very  valuable  to  the  practical  chemist. 
They  are  made  of  clay  free  from  lime,  mixed  with  sand  or  ground  ware  of 
the  same  description.  The  Hessian  and  Cornish  crucibles  are  among  the 
best.  Sometimes  a  mixture  of  plumbago  and  clay  is  employed  for  the  same 
purpose ;  and  powdered  coke  has  been  also  used  with  the  earth ;  such  cru- 
cibles bear  rapid  changes  of  temperature  with  impunity. 


256  M  A  N  a  A  N  E  s 


SECTION  IV. 

OXIDABLE  METALS  PROPER,  WHOSE  OXIDES  FORM  POWERFl  L 

BASES. 


MANGANESE. 

Manganese  is  tolerably  abundant  in  nature  in  an  oxidized  state,  forming, 
or  entering  into  the  composition  of,  several  interesting  minerals.  Traces  of 
this  substance  are  very  frequently  found  in  the  ashes  of  plants. 

Metallic  manganese,  or  perhaps,  strictly,  carbide  of  manganese,  may  be 
best  prepared  by  the  following  process.  The  carbonate  is  calcined  in  an 
open  vessel,  by  which  it  becomes  converted  into  a  dense  brown  powder ;  this 
is  intimately  mixed  with  a  little  charcoal,  and  about  one-tenth  of  its  weight 
of  anhydrous  borax.  A  charcoal  crucible  is  next  prepared  by  filling  a  Hes- 
sian or  Cornish  crucible  with  moist  charcoal-powder,  introduced  a  little  at 
a  time,  and  rammed  as  hard  as  possible.  A  smooth  cavity  is  then  scooped 
in  the  centre,  into  which  the  above-mentioned  mixture  is  compressed,  and 
covered  with  charcoal-powder.  The  lid  of  the  crucible  is  then  fixed,  and 
the  whole  arranged  in  a  very  powerful  wind-furnace.  The  heat  is  slowly 
raised  until  the  crucible  becomes  red-hot,  after  which  it  is  urged  to  its  maxi- 
mum for  an  hour  or  more.  When  cold,  the  crucible  is  broken  up,  and  the 
metallic  button  of  manganese  extracted. 

Manganese  is  a  greyish-white  metal,  resembling  some  varieties  of  cast- 
iron  ;  it  is  hard  and  brittle,  and  destitute  of  magnetic  properties.  Its  spe- 
cific gravity  is  about  8.  It  is  fusible  with  great  difl5culty,  and,  when  free 
from  iron,  oxidizes  in  the  air  so  readily,  that  it  requires  to  be  preserved  in 
naphtha.  Water  is  not  sensibly  decomposed  by  manga^iese  in  the  cold. 
Dilute  sulphuric  acid  dissolves  it  with  great  energy,  evolving  hydrogen. 

The  equivalent  of  manganese  is  assumed  to  be  27 -6 ;  its  symbol  is  Mn. 

Oxides  of  Manganese. — Seven  diflFerent  oxides  of  this  metal  are  described, 
but  two  out  of  the  number  are,  probably,  secondary  compounds. 

Protoxide MnO 

Sesquioxide Mn^Oj 

Binoxide MnOj 

Proto-sesquioxide  (red  oxide) Mng04=MnO,  MugOg 

Varvicite Mn407=Mn2032MnOa 

Manganic  acid MnOg 

Permanganic  acid MugO^ 

Protoxide,  MnO.  —  When  carbonate  of  manganese  is  heated  in  a  stream 
of  hydrogen  gas,  or  of  vapour  of  water,  the  carbonic  acid  is  disengaged, 
and  a  green- coloured  powder  left  behind,  which  is  the  protoxide.  Prepared 
at  a  dull  red-heat  only,  the  protoxide  is  so  prone  to  absorb  oxygen  from  the 
air,  that  it  cannot  be  removed  from  the  tube  without  change ;  but  when  at  a 
higher  temperature  it  appears  more  stable.     This  oxide  is  a  very  powerful 


MANGANESE.  257 

bac^e,  being  isomorphous  with  magnesia  and  zinc ;  it  dissolves  quietly  in 
dilute  acids,  neutralizing  them  completely  and  forming  salts,  which  have 
often  a  beautiful  pink  colour.  When  alkalis  are  added  to  solutions  of  these 
compounds  the  white  hydrated  oxide  first  precipitated  speedily  becomes 
brown  by  passing  into  a  higher  state  of  oxidation. 

Sesquioxide,  MujOg.  —  This  compound  occurs  in  nature  in  the  state  of 
hydrate ;  a  very  beautiful  crystallized  variety  is  found  at  Ilefeld,  in  the 
Hartx.  It  is  produced  artificially,  by  exposing  to  the  air  the  hydrated  prot- 
oxide, and  forms  the  principal  part  of  the  residue  left  in  the  iron  retort  when 
oxygen  gas  is  prepared  by  exposing  the  native  binoxide  to  a  moderate  red- 
heat.  The  colour  of  the  sesquioxide  is  brown  or  black,  according  to  its 
origin  or  mode  of  preparation.  It  is  a  feeble  base,  isomorphous  with  alu- 
mina ;  for,  when  gently  heated  with  diluted  sulphuric  acid,  it  dissolves  to  a 
red  liquid,  which,  on  the  addition  of  sulphate  of  potassa  or  of  ammonia, 
deposits  octahedral  crystals  having  the  constitution  of  common  alum ;  these 
are,  however,  decomposed  by  water.  Strong  nitric  acid  resolves  this  oxide 
into  a  mixture  of  protoxide  and  binoxide,  the  former  dissolving,  and  the 
latter  remaining  unaltered ;  while  hot  oil  of  vitriol  destroys  it  by  forming 
sulphate  of  the  protoxide,  and  liberating  oxygen  gas.  Heated  with  hydro- 
chloric acid,  chlorine  is  evolved,  as  with  the  binoxide,  but  to  a  smaller  extent. 

Binoxide,  MnO^. — The  most  common  ore  of  manganese ;  it  is  found  both 
massive  and  crystallized.  It  may  be  obtained  artificially  in  the  anhydrous 
state  by  gently  calcining  the  nitrate,  or  in  combination  with  water,  by  adding 
solution  of  bleaching-powder  to  a  salt  of  the  protoxide.  Binoxide  of  man- 
ganese has  a  black  colour,  is  insoluble  in  water,  and  refuses  to  unite  with 
acids.  It  is  decomposed  by  hot  hydrochloric  acid  and  by  oil  of  vitriol  in  the 
same  manner  as  the  sesquioxide. 

As  this  substance  is  an  article  of  commerce  of  considerable  importance, 
being  used  in  a  very  large  quantity  for  making  chlorine,  and  as  it  is  subject 
to  great  alteration  of  value  from  an  admixture  of  the  sesquioxide  and  several 
impurities,  it  becomes  desirable  to  possess  means  of  assaying  dill'erent  sam- 
ples that  may  be  presented,  with  a  view  of  testing  their  fitness  for  the  pur- 
poses of  the  manufacturer.  One  of  the  best  and  most  convenient  methods 
is  the  following :  —  50  grains  of  the  mineral,  reduced  to  a  very  fine  powder, 
are  put  into  the  little  vessel  employed  in  the  analysis  of  carbonates,'  together 
with  about  half  an  ounce  of  cold  water,  and  100  grains  of  strong  hydro- 
chloric acid ;  50  grains  of  crystallixed  oxalic  acid  are  then  added,  the  cork 
carrying  the  chloride  of  calcium  tube  is  fitted,  and  the  whole  quickly 
weighed  or  countei-poised.  The  application  of  a  gentle  heat  suffices  to  deter- 
mine the  action:  the  disengaged  chlorine  converts  the  oxalic  acid  into  car- 
bonic acid,  with  the  help  of  the  elements  of  water,  two  equivalents  of  car- 
bonic acid  representing  one  of  chlorine,  and  consequently  one  of  binoxide 
of  manganese.  Now,  the  equivalent  of  the  latter  substance,  43-0,  is  so 
nearly  equal  to  twice  that  of  carbonic  acid,  22,  that  the  loss  of  weight 
guttered  by  the  apparatus  when  the  reaction  has  has  become  complete,  and 
the  residual  gas  has  been  driven  olf  by  momentary  ebullition,  may  be  taken 
to  represent  the  quantity  of  real  binoxide  in  the  50  grains  of  the  sample 
It  is  obvious  that  the  little  apparatus  of  Will  and  Fresenius,  described  at 
page  229,  may  be  used  with  the  same  advantage. 

Red  oxide,  MUgO^,  or  probably  MnO-j-MngOg.  —  This  oxide  is  also  found 
native,  and  is  produced  artificially  by  heating  to  whitene^^s  the  binoxide  or 
sesquioxide,  or  by  exposing  the  protoxide  or  carbonate  to  a  red-heat  in  an 
open  vessel.  It  is  a  reddish-brown  substance,  incapa>)le  of  forming  salts, 
and  acted  upon  by  acids  in  the  same  manner  as  the  two  higher  oxides  ah'eady 

"  Sec  page  228. 
22* 


258  MANGANESE. 

described.     Borax  and  glass  in  a  fused  state  dissolve  this  substaLce,  and 
acquire  the  colour  of  the  amethyst. 

Varvicite,  Mn^O,,  or  Mn203-J-2Mn02. — A  natural  prodviCtion,  discovered 
by  Mr,  Phillips,  among  certain  specimens  of  manganese-ore  from  Warwick- 
shire ;  it  has  also  been  found  at  Ilefeld.  It  much  resembles  the  binoxide, 
but  is  harder  and  more  brilliant,  and  contains  water.  By  a  strong  heat, 
varvicite  is  converted  into  red  oxide,  with  disengagement  of  aqueous  vapour 
and  oxygen  gas. 

Chloride  of  manganese,  MnCl.  —  This  salt  may  be  prepared  in  a  state 
of  purity  from  the  dark  brown  liquid  residue  of  the  preparation  of  chlorine 
from  binoxide  of  manganese  and  hydrochloric  acid,  which  often  accumulates 
in  the  laboratory  to  a  considerable  extent  in  the  course  of  investigation ; 
from  the  pure  chloride,  the  carbonate  and  all  other  salts  can  be  conveniently 
obtained.  The  liquid  referred  to  consists  chiefly  of  the  mixed  chlorides  of 
manganese  and  iron ;  it  is  filtered,  evaporated  to  perfect  dryness,  and  then 
slowly  heated  to  dull  ignition  in  an  earthen  vessel,  with  constant  stirring. 
The  chloride  of  iron  is  thus  either  volatilized  or  converted  by  the  remaining 
water  into  insoluble  sesquioxide,  while  the  manganese-salt  is  unaffected.  On 
treating  the  greyish-looking  powder  thus  obtained  with  water,  the  chloride 
of  manganese  is  dissolved  out,  and  may  be  separated  by  filtration  from  the 
sesquioxide  of  iron.  Should  a  trace  of  the  latter  yet  remain,  it  may  be  got 
rid  of  by  boiling  the  liquid  for  a  few  minutes  with  a  little  carbonate  of  man- 
ganese. The  solution  of  chloride  has  usually  a  delicate  pink  colour,  which 
becomes  very  manifest  when  the  salt  is  evaporated  to  dryness.  A  strong 
solution  deposits  rose-coloured  tabular  crystals,  which  contain  4  equivalents 
of  water ;  these  are  very  soluble  and  deliquescent.  The  chloride  is  fusible 
at  a  red-heat,  is  decomposed  slightly  at  that  temperature  by  contact  of  air, 
and  is  dissolved  by  alcohol,  with  which  it  forms  a  crystallizable  compound. 

Sesquichloride,  Muj  Clg.  — When  precipitated  sesquioxide  of  manganese 
is  put  into  cold  dilute  hydrochloric  acid,  it  dissolves  quietly,  forming  a  red 
solution  of  sesquichloride.  Heat  disengages  chlorine,  and  occasions  the  pro- 
duction of  protochloride. 

Sulphate  of  protoxide  of  manganese,  MnO,SOg-|-7HO.  —  A  beautiful 
rose-coloured  and  very  soluble  salt,  isomorphous  with  sulphate  of  magnesia. 
It  is  prepared  on  a  large  scale  for  the  use  of  the  dyer,  by  heating,  in  a  close 
vessel,  binoxide  of  manganese  and  coal,  and  dissolving  the  impure  protoxide 
thus  obtained  in  sulphuric  acid,  with  the  addition  of  a  little  hydrochloric 
acid  towards  the  end  of  the  process.  The  solution  is  evaporated  to  dryness, 
and  again  exposed  to  a  red-heat,  by  which  the  sulphate  of  sesquioxide  of 
iron  is  decomposed.  Water  then  dissolves  out  the  pure  sulphate  of  manga- 
nese, leaving  the  sesquioxide  of  iron  behind.  The  salt  is  used  to  produce  a 
permanent  brown  dye,  the  cloth  steeped  in  the  solution  being  aftewards 
passed  through  a  solution  of  bleaching-powder,  by  which  the  protoxide  is 
changed  to  insoluble  hydrate  of  the  binoxide.  Sulphate  of  manganese 
sometimes  crystallizes  with  five  equivalents  of  water.  It  forms  a  double  salt 
with  sulphate  of  potassa. 

Carbonate  of  manganese. — Prepared  by  precipitating  the  protochloride 
by  an  alkaline  carbonate.  It  is  insoluble  and  buif-coloured,  or  sometimes 
nearly  white.  Exposed  to  heat,  it  loses  carbonic  acid,  and  absorbs  oxygen. 
Manganic  acid,  MnOg.  —  When  an  oxide  of  manganese  is  fused  with  an 
alkali,  an  additional  quantity  of  oxygen  is  taken  up  from  the  air,  and  a  deep 
green  saline  mass  results,  which  contains  a  salt  of  the  new  acid,  thus  formed 
under  the  influence  of  the  base.  The  addition  of  nitre,  or  chlorate  of 
potassa,  facilitates  the  production  of  manganic  acid.  Water  dissolves  this 
compound  very  readily,  and  the  solution,  concentrated  by  evaporation  in 
vacuo,  yields  green  crystals. 


IRON.  259 

Pebmangantc  acid,  Mn^O^.  —  When  manganate  of  potassa,  free  from  any 
great  excess  of  alkali,  is  put  into  a  large  quantity  of  water,  it  is  resolved 
into  hydrated  binoxide  of- manganese,  which  subsides,  and  a  deep  purple 
liquid,  containing  permanganate  of  potassa.  This  effect  is  accelerated  by 
heat.  The  changes  of  colour  accompanying  this  decomposition  are  very  re- 
markable, and  have  procured  for  the  substance  the  name  mineral  chameleon  ; 
excess  of  alkali  hinders,  in  some  measure,  the  reaction,  by  conferring  greater 
stability  on  the  manganate.  Permanganate  of  potassa  is  easily  prepared  on 
a  considerable  scale.  Equal  parts  of  very  finely  powdered  binoxide  of  man- 
ganese and  chlorate  of  potassa  are  mixed  with  rather  more  than  one  part  of 
\iydrate  of  potassa  dissolved  in  a  little  water,  and  the  whole  exposed,  after 
♦evaporation  to  dryness,  to  a  temperature  just  short  of  ignition.  The  mass 
is  treated  with  hot  water,  the  insoluble  oxide  separated  by  decantation,  and 
the  deep  purple  liquid  concentrated  by  heat,  until  crystals  form  upon  its 
surface  ;  it  is  then  left  to  cool.  The  crystals  have  a  dark  purple  colour,  and 
are  not  very  soluble  in  cold  water.  The  manganates  and  permanganates  are 
decomposed  by  contact  with  organic  matter ;  the  former  are  said  to  be  iso- 
morphous  with  the  sulphates,  and  the  latter  with  the  perchlorates. 


Salts  of  the  protoxide  of  manganese  are  very  easily  distinguished  by 
reagents. 

The  fixed  caustic  alkalis,  and  ammonia,  give  white  precipitates,  insoluble 
in  excess,  quickly  becoming  brown. 

The  carbonates  of  the  fixed  alkalis,  and  carbonate  of  ammonia,  give  white 
precipitates,  but  little  subject  to  change,  and  insoluble  in  e:^cess  of  carbonate 
of  ammonia. 

Sulphuretted  hydrogen  gives  no  precipitate,  but  sulphide  of  ammonium 
throws  down  insoluble,  flesh-coloured  sulphide  of  manganese,  which  is  very 
characteristic.  .  | 

Ferrocyanide  of  potassium  gives  a  white  precipitate. 

Manganese  is  also  easily  detected  by  the  blowpipe ;  it  gives  with  borax  an 
amethystine  bead  in  the  outer  or  oxidizing  flame,  and  a  colourless  one  in  the 
inner  flame.  Heated  upon  platinum  foil  with  carbonate  of  soda,  it  yields  a 
green  mass  of  manganate  of  soda. 


This  is  by  very  far  the  most  important  member  of  the  group  of  metals 
under  discusgion  ;  there  are  few  substances  to  which  it  yields  in  interest, 
when  it  is  considered  how  very  intimately  the  knowledge  of  the  properties 
and  uses  of  iron  is  connected  with  human  civilization. 

Metallic  iron  is  of  exceedingly  rare  occurrence ;  it  has  been  found  at 
Canaan,  in  Connecticut,'  forming  a  vein  about  two  inches  thick  in  mica-slate, 
but  it  invariably  enters  into  the  composition  of  those  extraordinary  stones 
known  to  fall  from  the  air,  called  meteorites.  Isolated  masses  of  soft  malleable 
iron  also,  of  large  dimensions,  lie  loose  upon  the  surface  of  the  earth  in  South 
America  and  elsewhere,  and  are  presumed  to  have  had  a  similar  origin : 
these  latter  contain,  in  common  with  the  iron  of  the  undoubted  meteorites, 
nickel.  In  an  oxidized  condition,  the  presence  of  iron  may  be  said  to  be 
universal;  it  constitutes  great  part  of  the  common  colouring  matter  of  rocks 
and  soils ;  it  is  contained  in  plants,  and  forms  an  essential  component  of  the 
blood  of  the  animal  body.  In  the  state  of  bisulphide  it  is  also  very  common 
Pure  iron  may  be  prepared,  according  to  Mitscherlich,  by  introducing  into 


'  Phillip's  Mineralogy,  fourth  edit.  p.  20i. 


260  IRON. 

a  Hessian  crucible  4  parts  of  fine  iron  wire  cut  smuU,  and  1  part  of  black 
oxide  of  iron.  This  is  covered  with  a  mixture  of  white  sand,  lime,  and  car- 
bunate  of  potassa,  in  the  proportions  used  for  glass-making,  and  a  cover  being 
closely  applied,  the  crucible  is  exposed  to  a  very  high  degree  of  heat.  A 
button  of  pure  metal  is  thus  obtained,  the  traces  of  carbon  and  silicum  pre- 
sent in  the  wire  having  been  removed  by  the  oxygen  of  the  oxide. 

Pure  iron  has  a  white  colour  and  perfect  lustre ;  it  is  extremely  soft  and 
tough,  and  has  a  specific  gravity  of  7-8.  The  crystalline  form  is  probably 
the  cube,  to  judge  from  appearances  now  and  then  exhibited.  In  good  bar- 
iron  or  wire  a  distinct  fibrous  texture  may  always  be  observed  when  the 
metal  has  been  attacked  by  rusting  or  by  the  application  of  an  acid,  and 
upon  the  perfection  of  this  fibre  much  of  its  strength  and  value  depends. 
Iron  is  the  most  tenacious  of  all  the  metals,  a  wire  g'jth  of  an  inch  in  diame- 
ter bearing  a  weight  of  601b.  It  is  very  difiicult  of  fusion,  and  before  be- 
coming liquid  passes  through  a  soft  or  pasty  condition.  Pieces  of  iron 
pressed  or  hammered  together  in  this  state  cohere  into  a  single  mass ;  the 
operation  is  termed  welding,  and  is  usually  performed  by  sprinkling  a  little 
Band  over  the  heated  metal,  which  combines  with  the  superficial  film  of  oxide, 
forming  a  fusible  silicate,  which  is  subsequently  forced  out  from  between 
the  pieces  of  iron  by  the  pressure  applied ;  clean  surfaces  of  metal  are  thus 
presented  to  each  other,  and  union  takes  place  without  difficulty. 

Iron  does  not  oxidize  in  dry  air  at  common  temperatures ;  heated  to  red- 
ness, it  becomes  covered  with  a  scaly  coating  of  black  oxide,  and  at  a  high 
white-heat  burns  brilliantly,  producing  the  same  substance ;  in  oxygen  gas 
the  combustion  occurs  with  still  greater  ease.  The  finely  divided  spongy 
metal,  prepared  by  reducing  the  oxide  by  hydrogen  gas,  takes  fire  spontane- 
ously in  the  air.*  Pure  water,  free  from  air  and  carbonic  acid,  does  not 
tarnish  a  surface  of  polished  iron,  but  the  combined  agency  of  free  oxygen 
and  moisture  speedily  leads  to  the  production  of  rust,  which  is  a  hydrate  of 
the  sesquioxide.  The  rusting  of  iron  is  wonderfully  promoted  by  the  pre- 
sence of  a  little  acid  vapour.*  At  a  red-heat  iron  decomposes  water,  evolving 
hydrogen,  and  passing  into  the  black  oxide.  Dilute  sulphuric  and  hydro- 
chloric acids  dissolve  it  freely  with  separation  of  hydrogen.  Iron  is  strongly 
magnetic  up  to  a  red-heat,  when  it  loses  all  traces  of  that  remarkable  pro- 
perty. 

The  equivalent  of  iron  is  28,  and  its  symbol  Fe. 

Four  compounds  of  iron  and  oxygen  are  described. 

Protoxide FeO 

Sesquioxide  (peroxide)   FCgOg 

Protosesquioxide  (black  oxide)  Fe304=FeO,  FcgOg 

Ferric  acid FeOg 

Protoxide,  FeO.  —  This  is  a  very  powerful  base,  neutralizing  acids  com- 
pletely, and  isomorphous  with  magnesia,  oxide  of  zinc,  &c.  It  is  almost 
unknown  in  a  separate  state,  from  its  extreme  proneness  to  absorb  oxygen 
and  pass  into  the  sesquioxide.  When  a  salt  of  this  substance  is  mixed  with 
caustic  alkali  or  ammonia,  a  bulky  whitish  precipitate  of  hydrate  of  the  pro- 
toxide falls,  which  becomes  nearly  black  when  boiled,  the  water  being  sepa- 

»  When  obtained  at  a  heat  l)e1ow  redness.— R.  B. 

^  Tlic  rusting  of  iron  proceeds  with  rapidity  after  it  once  begins,  extending  from  the  point 
first  affect<Hi.  Iron  rust  contains  ammonia,  resulting  from  the  combination  of  the  na.sceiit 
hydro2;en  of  decomposed  water  uniting  with  dissolved  nitrogen.  This  is  an  important  point 
in  medico-legal  investigations,  as  it  is  considered,  that,  when  stains  on  a  steel  instrument 
yield  ammonia  by  the  action  of  potassa,  the  presence  of  organic  matter  is  proved ;  but  as  rut;t 
ron tains  ammonia,  it  becomes  necessary  to  ascertain  its  absence,  or  drive  it  off,  previous  to 
tfurauug  with  potassa. — R.  B. 


IRON.  261 

rated.  This  hydrate  exposed  to  the  air,  very  rapidly  changes,  becoming 
green  and  ultimately  red-brown.  The  soluble  salts  of  protoxide  of  iron  have 
commonly  a  delicate  pale  green  colour,  and  a  nauseous  metallic  taste. 

Sesquioxide,  Fe^Og.  — A  feeble  base,  isomorphous  with  alumina.  Sesqui- 
oxide  of  iron  occurs  native,  most  beautifully  crystallized  as  specular  iron  ore 
in  the  island  of  Elba,  and  elsewhere ;  also  as  red  and  brown  hcematites,  the 
latter  being  a  hydrate.  It  is  artificially  prepared  by  precipitating  a  solution 
of  sulphate  of  the  sesquioxide  or  the  sesquichloride  of  iron  by  excess  of  am- 
monia, and  washing,  drying,  and  igniting  the  yellowish-brown  hydrate  thus 
produced ;  fixed  alkali  must  not  be  used  in  this  operation,  as  a  portion  is  re- 
tained by  the  oxide.  In  fine  powder,  this  oxide  has  a  full  red  colour,  and  is 
used  as  a  pigment,  being  prepared  for  the  purpose  by  calcination  of  the  sul- 
phate of  the  protoxide ;  the  tint  vai'ies  somewhat  with  the  temperature  to 
which  it  has  been  exposed.  This  oxide  is  unaltered  in  the  fire,  although 
easily  reduced  at  a  high  temperature  by  carbon  or  hydrogen.  It  dissolves 
in  acids,  with  difficulty  after  strong  ignition,  forming  a  series  of  reddish 
salts,  which  have  an  acid  reaction  and  an  astringent  taste.  Sesquioxide  of 
iron  is  not  acted  upon  by  the  magnet.* 

Black  oxide  ;  magnetic  oxide  ;  loadstone, 
FCjOj.  —  A  natural  product,  one  of  the  most  val 
found  in  regular  octahedral  crystals,  which  are  magnetic.  It  may  be  pre- 
pared by  mixing  due  proportions  of  salts  of  the  protoxide  and  sesquioxide 
of  iron,  precipitating  them  by  excess  of  alkali,  and  then  boiling  the  mixed 
hydrates,  when  the  latter  unite  to  a  black  sandy  substance,  consisting  of 
minute  crystals  of  the  magnetic  oxide.  This  oxide  is  the  chief  product  of 
the  oxidation  of  iron  at  a  high  temperature  in  the  air  and  in  aqueous  vapour. 
It  is  incapable  of  forming  salts. 

Ferric  acid,  FeOg. — A  very  remarkable  compound  of  recent  discovery. 
The  simplest  mode  of  preparing  it  is  to  heat  to  full  redness,  for  an  hour,  in 
a  covered  crucible,  a  mixture  of  one  part  of  pure  sesquioxide  of  iron,  and 
four  parts  of  dry  nitre.  The  brown,  porous,  deliquescent  mass  is  treated 
when  cold  with  ice-cold  water,  by  which  a  deep  amethystine  red  solution  of 
ferrate  of  potassa  is  obtained.  This  gradually  decomposes  even  in  the  cold, 
evolving  oxygen  gas,  and  depositing  sesquioxide ;  by  heat  the  decomposition 
is  very  rapid.  The  solution  of  ferrate  of  potassa  gives  no  precipitate  with 
salts  of  lime,  magnesia,  or  strontia,  but  when  mixed  with  one  of  baryta,  a 
deep  crimson,  insoluble  compound  falls,  which  is  a  ferrate  of  that  base,  and 
is  very  permanent. 

Protochloride  of  iron,  FeCl.  —  Formed  by  transmitting  dry  hydrochloric 
acid  gas  over  red-hot  metallic  iron,  or  by  dissolving  iron  in  hydrochloric  acid. 
The  latter  solution  yields,  when  duly  concentrated,  green  crystals  of  the  pro- 
tochloride, containing  4  equivalents  of  water;  they  are  very  soluble  and 
deliquescent,  and  rapidly  oxidize  in  the  air. 

Sesquichloride  of  iron,  FegClg.  —  Usually  prepared  by  dissolving  sesqui- 
oxide in  hydrochloric  acid.  The  solution,  evaporated  to  a  syrupy  consistence, 
deposits  red,  hydrated  crystals,  which  are  very  soluble  in  water  and  alcohol. 
It  forms  double  salts  with  chloride  of  potassium  and  sal-ammoniac.  When 
evaporated  to  dryness  and  strongly  heated,  much  of  the  chloride  is  decom- 
posed, yielding  sesquioxide  and  hydrochloric  acid ;  the  remainder  sublimes, 
and  afterwards  condenses  in  the  form  of  small  brilliant  red  crystals,  which 
•deliquesce  rapidly.  The  solution  of  sesquichloride  of  iron  is  capable  of  dis- 
solving a  large  excess  of  recently  precipitated  hydrate  of  the  sesquioxide,  by 

»In  the  form  of  hydrate,  Fe<}03+3HO,  as  recently  precipitated  fi-om  the  persulphate  by  am- 
monia, it  constitutes  the  antidote  for  arsenious  acid.  The  aflftnity  for  water  in  this  case  is  not 
strong— the  hydrate  gradually  decowiposing  even  when  kept  under  water,  its  colour  fwnD0 
from  yellowish  brown  to  red.— R.  B. 


262  IRON. 

which  it  acquires  a  much  darker  colour.  Anhydrous  sesquichloride  of  iron 
is  also  produced  by  the  action  of  chlorine  upon  the  heated  metal. 

Protiodide  of  iron,,  Fel.  —  This  is  an  important  medicinal  preparation; 
it  is  easily  made  by  digesting  iodine  with  water  and  metallic  iron.  The  so- 
lution is  pale  green,  and  yields,  on  evaporation,  crystals  resembling  those  of 
the  chloride,  which  rapidly  oxidize  on  exposure  to  air.  It  is  best  preserved 
in  solution  in  contact  with  excess  of  iron.'  A  sesqui-iodide  of  iron  exists, 
which  is  yellowish-red  and  soluble. 

Sulphides  of  iron. — Several  compounds  of  iron  and  sulphur  are  de- 
scribed ;  of  these  the  two  most  important  are  the  following,  FrotosulphiJe^ 
FeS,  is  a  blackish,  brittle  substance,  attracted  by  the  magnet,  formed  by 
heating  together  iron  and  sulphur.  It  is  dissolved  by  dilute  acids  with  evo- 
lution of  sulphuretted  hydrogen  gas,  and  is  constantly  employed  for  that 
purpose  in  the  laboratory,  being  made  by  projecting  into  a  red-hot  crucible 
a  mixture  of  2^  parts  of  sulphur  and  4  parts  of  iron  filings  or  borings  of 
cast-iron,  and  excluding  the  air  as  much  as  possible.  The  same  substance 
is  formed  when  a  bar  of  white  hot-iron  is  brought  in  contact  with  sulphur. 
The  bisulphide  of  iron,  FeSg,  iron  pyrites,  is  a  natural  product,  occurring  in 
rocks  of  all  ages,  and  evidently  formed  in  many  cases  by  the  gradual  de- 
oxidation  of  sulphate  of  iron  by  organic  matter.  It  has  a  brass-yellow 
colour,  is  very  hard,  not  attracted  by  the  magnet,  and  not  acted  upon  by 
dilute  acids.  Exposed  to  heat,  sulphur  is  expelled,  and  an  intermediate  sul- 
phide, analogous  probably  to  the  black  oxide,  is  produced.  This  substance 
also  occurs  native,  under  the  name  of  magnetic  pyrites.  The  bisulphide  is 
sometimes  used  in  the  manufacture  of  sulphuric  acid. 

Compounds  of  iron  with  phosphorus,  carbon,  and  silicium  exist,  but  little 
is  known  respecting  them  in  a  definite  state.  The  carbide  is  contained  in 
cast-iron  and  in  steel,  to  which  it  communicates  ready  fusibility ;  the  silicium- 
compound  is  also  found  in  cast-iron.  Phosphorus  is  a  very  hurtful  substance 
in  bar-iron,  as  it  renders  it  brittle  or  cold-short. 

Sulphate  of  protoxide  of  iron;  green  vitriol,  FeOjSOg-j-THO. — This 
beautiful  and  important  salt  may  be  obtained  by  directly  dissolving  iron  in 
dilute  sulphuric  acid ;  it  is  generally  prepared,  however,  and  that  on  a  very 
large  scale,  by  contact  of  air  and  moisture  with  common  iron  pyrites,  which, 
by  absorption  of  oxygen,  readily  furnishes  the  substance  in  question.  Heaps 
of  this  material  are  exposed  to  the  air  until  the  decomposition  is  sufficiently 
advanced ;  the  salt  produced  is  then  dissolved  out  by  water,  and  the  solution 
made  to  crystallize.  It  forms  large  green  crystals,  of  the  composition  above 
stated,  which  slowly  effloresce  and  oxidize  in  the  air ;  it  is  soluble  in  about 
twice  its  weight  of  cold  water.  Crystals  containing  4,  and  also  2  equiva- 
lents of  water,  have  been  obtained.  Sulphate  of  protoxide  of  iron  forms 
double  salts  with  the  sulphates  of  potassa  and  ammonia. 

Sulphate  op  sesquioxide  of  iron,  FejOgjSSOg.  —  Prepared  by  adding  to 
a  solution  of  the  protosalt  exactly  one-half  as  much  sulphuric  acid  as  it 
already  contains,  raising  the  liquid  to  the  boiling-point,  and  then  dropping 
in  nitric  acid  until  the  solution  ceases  to  blacken  by  such  addition.  The  red 
liquid  thus  obtained  furnishes,  on  evaporation  to  dryness,  a  buff-coloured 
amorphous  mass,  which,  when  put  into  water,  very  slowly  dissolves.  With 
the  sulphates  of  potassa  and  ammonia,  this  salt  yields  compounds  having 
the  form  and  constitution  of  the  alums ;  the  crystals  are  nearly  destitute  of 
colour.  These  latter  are  decomposed  by  water,  and  sometimes  by  long  keep- 
ing when  in  a  dry  state.  They  are  best  prepai-ed  by  exposing  to  spontaneous 
evaj:  oration  a  solution  of  sulphate  of  sesquioxide  of  iron  to  which  sulphate 
of  putassa  or  of  ammonia  has  been  added. 

•  Or  protev^#d  from  the  action  of  oxygen  by  pure  honey,  or  other  saccharine  substance, 
hi  the  proportion  of  one  part  to  three  of  the  solution. — U.  B, 


IRON.  263 

Nitrate  of  the  psotoxide  of  iron,  FeOjNOg. -^When  dilute  cold  nitric 
acid  is  made  to  act  to  saturation  upon  protosulpliide  of  iron,  and  the  solu- 
tion evaporated  in  vacuo,  pale  green  and  very  soluble  crystals  of  protonitrate 
are  obtained,  which  are  very  subject  to  alteration.  The  nitrate  of  the  ses- 
quioxide  is  readily  formed  by  pouring  nitric  acid,  slightly  diluted,  upon  iron ; 
it  is  a  deep  red  liquid,  apt  to  deposit  an  insoluble  basic  salt,  and  is  used  in 
dyeing. 

Carbonate  of  protoxide  of  iron,  FeOjCOa-  —  The  white  precipitate  ob- 
tained by  mixing  solutions  of  protosalt  of  iron  and  alkaline  carbonate ;  it 
cannot  be  washed  and  dried  without  losing  carbonic  acid  and  absorbing 
oxygen.  This  substance  occurs  in  nature  as  spathose  iron  ore,  associated  with 
variable  quantities  of  carbonate  of  lime  and  of  magnesia ;  and  also  in  the 
common  day  iron-stone,  from  which  nearly  all  the  British  iron  is  made.  It 
is  often  found  in  mineral  waters,  being  soluble  in  excess  of  carbonic  acid ; 
such  waters  are  known  by  the  rusty  matter  they  deposit.  No  carbonate  of 
the  sesquioxide  is  known. 

The  phosphates  of  iron  are  all  insoluble.' 


Salts  of  the  protoxide  of  iron  are  thus  distinguished : — 

Caustic  alkalis,  and  ammonia,  give  nearly  white  precipitates,  insoluble  in 
excess  of  the  reagent,  rapidly  becoming  green,  and  ultimately  brown,  by  ex- 
posure to  air. 

Alkaline  carbonates,  and  carbonate  of  ammonia,  throw  down  the  white 
carbonate,  also  very  subject  to  change. 

Sulphuretted  hydrogen  gives  no  precipitate,  but  sulphide  of  ammonium 
throws  down  black  protosulphide  of  iron,  soluble  in  dilute  ajj^ds. 

Ferrocyanide  of  potassium  gives  a  nearly  white  precipitat^j  becoming  deep 
blue  on  exposure  to  air. 

Salts  of  the  sesquioxide  are  thus  characterized : — 

Caustic  alkalis,  and  ammonia,  give  foxy-red  precipitates  of  hydrated  ses- 
quioxide, insoluble  in  excess. 

The  carbonates  behave  in  a  similar  manner,  the  carbonic  acid  escaping. 

Sulphuretted  hydrogen  gives  a  nearly  white  precipitate  of  sulphur,  and 
reduces  the  sesquioxide  to  protoxide. 

Sulphide  of  ammonium  gives  a  black  precipitate,  slightly  soluble  in  excess. 

Ferrocyanide  of  potassium  yields  Prussian  blue. 

Tincture  or  infusion  of  gall-nuts  strikes  intense  bluish-black  with  th« 
most  dilute  solutions  of  salts  of  sesquioxide  of  iron. 


Iron  Manufacture.  —  This  most  important  branch  of  industry  consists,  as 
now  conducted,  of  two  distinct  parts ;  viz.,  the  production  from  the  ore  of  a 
fusible  (carbide)  of  iron,  and  the  subsequent  decomposition  of  the  carbide, 
and  its  conversion  into  pure  or  malleable  iron. 

The  clay  iron  ore  is  found  in  association  with  coal,  forming  thin  beds  or 
nodules ;  it  consists,  as  already  mentioned,  of  carbonate  of  iron  mixed  with 
clay ;  sometimes  lime  and  magnesia  are  also  present.    It  is  broken  in  pieces, 

»  Phosphate  of  protoxide  op  Iron,  2FeO,  H0,P05,  is  formed  when  a  eolution  of  common 
phosphate  of  soda  is  added  to  a  solution  of  protosulphate  of  iron.  It  fnl'.s  hs  a  wliite  preci- 
pitate, gradually  becoming  bluish  by  the  action  of  the  air;  it  is  soluble  in  acids,  from  wbieh 
ammonia  again  precipitates  it,  and  re-dissolves  the  precipitate  when  added  in  excess.  The 
blue  phosphate  contains  perphosphate. 

Phosphate  of  sesquioxide  of  Iron  is  formed  by  adding  common  phosphate  of  soda  to  per- 
sulphate or  perchloride  of  iron;  a  white  precipitate  is  produced  insoluble  in  ammonia  unless 
an  excess  of  pliosphate  of  soda  be  present.  Digested  with  the  fixed  alkalis  or  ammonia  it 
becomes  brown. — 11.  B. 


264 


IRON. 


and  exposed  to  heat  in  a  furnace  resembling  a  lime-kiln,  by  which  the  water 
and  carbonic  acid  are  expelled,  and  the  ore  rendered  dark-coloured,  denser, 
and  also  magnetic ;  it  is  then  ready  for  reduction.  The  furnace  in  which 
this  operation  is  performed  is  usually  of  very  large  dimensions,  fifty  feet  or 
naore  in  height,  and  constructed  of  brick  work  with  great  solidity,  the 
interior  being  lined  with  excellent  fire-bricks ;  the  figure  will  be  at  once 
understood  from  the  sectional  drawing  (fig.  149).     The  furnace  is  close  at 

Fig.  149. 


the  bottom,  the  fire  being  maintained  by  a  powerful  artificial  blast  introduced 
by  two  or  three  tuyere-pipes,  as  shown  in  the  section.  The  materials,  con- 
sisting of  due  proportions  of  coke  or  carbonized  coal,  roasted  ore,  and  lime- 
stone, are  constantly  supplied  from  the  top,  the  operation  proceeding  con- 
tinuously night  and  day,  often  for  years,  or  until  the  furnace  is  judged  to 
require  repair.  In  the  upper  part  of  the  furnace,  where  the  temperature  is 
still  very  high,  and  where  combustible  gases  abound,  the  iron  of  the  ore  is 
probably  reduced  to  the  metallic  state,  being  disseminated  through  the 
earthy  matter  of  the  ore ;  as  the  whole  sinks  down  and  attains  a  still  higher 
degree  of  heat,  the  iron  becomes  converted  into  carbide  by  cementation, 
while  the  silica  and  alumina  unite  with  the  lime,  purposely  added,  to  a  kind 
of  glass  or  slag,  nearly  free  from  oxide  of  iron.  The  carbide  and  slag,  both 
m  a  melted  state,  reach  at  last  the  bottom  of  the  furnace,  where  they  arrange 
themselves  in  the  order  of  their  densities ;  the  slag  flows  out  at  certain 
apertures  contrived  for  the  purpose,  and  the  iron  is  discharged  from  time  to 
time,  and  suffered  to  run  into  rude  moulds  of  sand  by  opening  an  orifice  at  the 


IRON.  265 

bottom  of  the  recipient,  previously  stopped  with  clay.  Such  is  the  origia 
of  crude  or  or  cast-iron,  of  which  there  are  several  varieties,  distinguished 
by  differences  of  colour,  hardness,  and  composition,  and  known  by  the  names 
of  grey,  black,  and  v^hite  iron.  The  first  is  for  most  purposes  the  best,  as  it 
admits  of  being  filed  and  cut  with  perfect  ease.  The  black  and  grey  kinds 
probably  contain  a  mechanical  admixture  of  graphite,  which  separates  during 
solidification. 

A  great  improvement  has  been  made  in  the  above  described  process,  by 
substituting  raw  coal  for  coke,  and  blowing  hot  air,  instead  of  cold,  into  the 
furnace.  This  is  effected  by  causing  the  air,  on  leaving  the  blowing-machine, 
to  circulate  through  a  system  of  red-hot  iron  pipes,  until  its  temperature 
becomes  high  enough  to  melt  lead.  This  alteration  has  already  effected  a 
prodigious  saving  in  fuel,  without,  it  appears,  any  injury  to  the  quality  of 
the  product. 

The  conversion  of  cast  into  bar-iron  is  effected  by  an  operation  called 
puddling  ;  previous  to  which,  however,  it  commonly  undergoes  a  process  the 
theory  of  which  is  not  perfectly  intelligible.  It  is  remelted,  and  suddenly 
cooled,  by  which  it  becomes  white,  crystalline,  and  exceedingly  hard :  in  this 
state  it  is  called  fine-metal.  The  puddling  process  is  conducted  in  an  ordi- 
nary reverberatory  furnace,  into  which  the  charge  of  fine-metal  is  introduced 
by  a  side  aperture.  This  is  speedily  melted  by  the  flame,  and  its  surface 
covered  with  a  crust  of  oxide.  The  workman  then,  by  the  aid  of  an  iron 
tool,  diligently  stirs  the  melted  mass,  so  as  intimately  to  mix  the  oxide  with 
the  metal ;  he  now  and  then  also  throws  in  a  little  water,  with  a  view  of  pro- 
moting more  rapid  oxidation.  Small  jets  of  blue  flame  soon  appear  upon 
the  surface  of  the  iron,  and  the  latter,  after  a  time,  begins  to  lose  its  fluidity, 
and  acquires,  in  succession,  a  pasty  and  a  granular  condition.  At  this  point, 
the  fire  is  strongly  urged,  the  sandy  particles  once  more  cohere,  and  the 
contents  of  the  furnace  now  admit  of  being  formed  into  several  large  balls 
or  masses,  which  are  then  withdrawn,  and  placed  under  an  immense  hammer, 
moved  by  machinery,  by  which  each  becomes  quickly  fashioned  into  a  rude 
bar.  This  is  re-heated,  and  passed  between  grooved  cast-iron  rollers,  and 
drawn  out  into  a  long  bar  or  rod.  To  make  the  best  iron,  the  bar  is  cut  into 
a  number  of  pieces,  which  are  afterwards  piled  or  bound  together,  again 
raised  to  a  welding  heat,  and  hammered  or  rolled  into  a  single  bar ;  and  this 
process  oi  piling  ov  fagotting  is  sometimes  twice  or  thrice  repeated,  the  iron 
becoming  greatly  improved  thereby. 

The  general  nature  of  the  change  in  the  puddling  furnace  is  not  difficult 
to  explain.  Cast-iron  consists  essentially  of  iron  in  combination  with  carbon 
and  silicium ;  when  strongly  heated  with  oxide  of  iron,  those  compounds  un- 
dergo decomposition,  the  carbon  and  silicium  becoming  oxidized  at  the  ex- 
pense of  the  oxygen  of  the  oxide.  As  this  change  takes  place,  the  metal 
gradually  loses  its  fusibility,  but  retains  a  certain  degree  of  adhesiveness, 
80  that  when  at  last  it  comes  under  the  tilt-hammer,  or  between  the  rollers, 
the  particles  of  iron  become  agglutinated  into  a  solid  mass,  while  the  readily 
fusible  silicate  of  the  oxide  is  squeezed  out  and  separated. 

All  these  processes  are,  in  Great  Britain,  performed  with  coal  or  coke, 
but  the  iron  obtained  is,  in  many  respects,  inferior  to  that  made  in  Sweden 
and  Russia  from  the  magnetic  oxide,  by  the  use  of  wood  charcoal,  a  fuel  too 
dear  to  be  extensively  employed  in  England.  Plate-iron  is,  however,  some- 
times made  with  charcoal. 

Steel. — -A  very  remarkable,  and  most  useful  substance,  prepared  by  heat 
ing  iron  in  contact  with  charcoal.  Bars  of  Swedish  iron  are  embedded  in 
charcoal  powder,  contained  in  a  large  rectangular  ci-ucible  or  chest  of  some 
substance  capable  of  resisting  the  fire,  and  exposed  for  many  hours  to  a  full 
red-heat.  The  iron  takes  up,  under  these  circumstances,  from  lo  to  1  7 
23 


266  A  R  I  D  1  U  M  . 

per  cent,  of  carbon,  becoming  harder,  and  at  the  same  time  fusible,  with  a 
certain  diminution,  however,  of  malleability.  The  active  agent  in  this  ce- 
mentation process  is  probably  carbonic  oxide ;  the  oxygen  of  the  air  in  the 
crucible  combines  with  the  carbon,  to  form  that  substance,  which  is  after- 
wards decomposed  by  the  heated  iron,  one  half  of  its  carbon  being  abstracted 
by  the  latter.  The  carbonic  acid  thus  formed  takes  up  an  additional  dose 
of  carbon  from  the  charcoal,  and  again  becomes  carbonic  oxide,  the  oxygen, 
or  rather  the  carbonic  acid,  acting  as  a  carrier  between  the  charcoal  and  the 
"•netal.  The  product  of  this  operation  is  called  blistered  steel,  from  the  blis- 
ered  and  rough  appearance  of  the  bars ;  the  texture  is  afterwards  improved 
nd  equalized  by  welding  a  number  of  these  bars  together,  and  drawing  the 
whole  out  under  a  light  tilt-hammer. 

The  most  perfect  kind  of  steel  is  that  which  has  undergone  fusion,  having 
been  cast  into  ingot-moulds,  and  afterwards  hammered :  of  this  all  fine  cut- 
ting instruments  are  made ;  it  is  difficult  to  forge,  requiring  great  skill  and 
care  on  the  part  of  the  operator. 

Steel  may  also  be  made  directly  from  some  particular  varieties  of  cast- 
iron,  as  that  from  spathose  iron  ore,  containing  a  little  manganese.  The 
metal  is  retained,  in  a  melted  state,  in  the  hearth  of  a  furnace,  while  a 
stream  of  air  plays  upon  it,  and  causes  partial  oxidation  ;  the  oxide  pro- 
duced reacts,  as  before  stated,  on  the  carbon  of  the  iron,  and  withdraws  a 
portion  of  that  element.  When  a  proper  degree  of  stiffness  or  pastiness  is 
observed  in  the  residual  metal,  it  is  withdrawn,  and  hammered  or  rolled  into 
bars.  The  wootz,  or  native  steel  of  India,  is  probably  made  in  this  manner. 
Annealed  cast-iron,  sometimes  called  run-steel,  is  now  much  employed  as  a 
substitute  for  the  more  costly  products  of  the  forge;  the  articles,  when  cast, 
are  embedded  in  powdered  iron  ore,  or  some  earthy  material,  and,  after  be- 
ing exposed  to  a  moderate  red-heat  for  some  time,  are  allowed  slowly  to 
cool,  by  which  a  very  extraordinary  degree  of  softness  and  malleability  is 
attained.  It  is  very  possible  that  some  little  decarbonization  may  take  place 
during  this  process. 

The  most  remarkable  property  of  steel  is  that  of  becoming  exceedingly 
hard  when  quickly  cooled ;  when  heated  to  redness,  and  suddenly  quenched 
in  cold  water,  steel,  in  fact,  becomes  capable  of  scratching  glass  with  fa- 
cility ;  if  re-heated  to  redness,  and  once  more  left  to  cool  slowly,  it  again 
becomes  nearly  as  soft  as  ordinary  iron,  and,  between  these  two  conditions, 
any  required  degree  of  hardness  may  be  attained.  The  articles,  forged  into 
shape,  are  first  hardened  in  the  manner  described ;  they  are  then  tempered, 
or  let  doivn,  by  exposure  to  a  proper  degree  of  annealing  heat,  which  is  often 
judged  of  by  the  colour  of  the  thin  film  of  oxide  which  appears  on  the 
polished  surface.  Thus,  a  temperature  of  about  430°  (221°C),  indicated  by 
a  faint  straw-colour,  gives  the  proper  temper  for  razors ;  that  for  scissors, 
pen-knives,  &c.,  will  be  comprised  between  470°  (243°C)  and  490°  (254oC), 
and  be  attended  by  a  full  yellow  or  brown  tint.  Swords  and  watch-springs 
require  to  be  softer  and  more  elastic,  and  must  be  heated  to  550°  (288°C)  or 
560°  (293°C),  or  until  the  surface  becomes  deep  blue.  Attention  to  these 
colours  has  now  become  of  less  importance,  as  metal  baths  are  often  sub- 
stituted for  the  open  fire  in  this  operation. 


Arii»ium  (from  'Aptjs,  Mars,  and  e75os,  appearance)  from  the  resemblance 
of  its  oxide  to  oxide  of  iron.  Ulgren  considers  this  as  a  new  metal.  He 
found  it  in  the  chrome  iron  from  Roros,  and  in  iron  ore  from  Oernstolso. 
There  are  stir  doubts  hanging  over  the  existence  of  this  metal. 


CHROMIUM.  267 


CHROMIUM. 

^'hromium  is  found  in  the  state  of  oxide,  in  combination  -witli  oxide  of 
W,*n,  in  some  abundance  in  tlie  Shetland  Islands,  and  elsewhere ;  as  chro- 
mate  of  lead,  it  constitutes  a  very  beautiful  mineral,  from  which  it  was  first 
obtained.  The  metal  itself  is  got  in  a  half-fused  condition  by  mixing  the 
oxide  with  one-fifth  of  its  weight  of  charcoal-powder,  inclosing  the  mixture 
in  a  crucible  lined  with  charcoal,  and  then  subjecting  it  to  the  very  highest 
heat  of  a  powerful  furnace.  It  is  hard,  greyish-white,  and  brittle ;  of  5-9 
specific  gravity,  and  exceedingly  difficult  of  fusion.  Chromium  is  but  little 
oxidable,  being  scarcely  attacked  by  the  most  powerful  acids ;  it  forms  at 
least  four  compounds  with  oxygen,  corresponding  to,  and  probably  ismor- 
phous  with,  those  of  iron. 

The  equivalent  of  chromium  is  26-8  ;  its  symbol  is  Cr. 

Protoxide  of  chromium,  CrO. — When  potassa  is  added  to  a  solution  of 
the  protochloride  of  chromium,  a  brown  precipitate  falls,  which  speedily 
passes  to  deep  foxy  red,  with  disengagement  of  hydrogen.  The  protoxide, 
in  the  state  of  the  pale  greenish  hydrate,  is  perhaps  obtained  when  ammonia 
is  substituted  for  potassa  in  the  preceding  experiment.  This  substance  is  a 
powerful  base,  forming  pale  blue  salts,  which  absorb  oxygen  with  extreme 
avidity.  The  double  sulphate  of  protoxide  of  chromium  and  potassa  con- 
tains 6  eq.  of  water,  like  the  other  members  of  the  same  group. 

Protosesquioxide  of  chromium,  CrO-j-CrjOg,  is  tlie  above  brownish-red 
precipitate  produced  by  the  action  of  water,  upon  the  protoxide.  The  de- 
composition is  not  complete  without  boiling.  This  oxide  corresponds  with 
the  magnetic  oxide  of  iron,  and  is  not  salifiable. 

Sesquioxide  of  chromium,  CrgOg. — When  chromate  of  mercury,  prepared 
by  mixing  solutions  of  the  nitrate  of  suboxide  of  mercury  and  of  chromate 
or  bichromate  of  potassa,  is  exposed  to  a  red-heat,  it  is  decomposed,  pure 
sesquioxide  of  chromium  having  a  fine  green  colour,  remaining.  In  this 
state  the  oxide  is,  like  alumina  after  ignition,  insoluble  in  acids.  From  a 
solution  of  sesquioxide  of  chromium  in  potassa  or  soda,  green  gelatinous 
hydrated  sesquioxide  of  chromium  is  separated  on  standing.  When  finely 
powdered  and  dried  over  sulphuric  acid,  its  formula  is  CrjOj-f-^HO.  A  hy- 
drate may  also  be  had  by  boiling  a  somewhat  dilute  solution  of  bichromate 
of  potassa,  strongly  acidulated  by  hydrochloric  acid,  with  small  successive 
portions  of  sugar  or  alcohol ;  in  the  former  case,  carbonic  acid  escapes ;  in 
the  latter  a  substance  called  aldehyde  and  acetic  acid  are  formed,  substances 
with  which  we  shall  become  acquainted  in  organic  chemistry,  and  the  chromic 
acid  of  the  salt  becomes  converted  into  sesquichloride  of  chromium,  the 
colour  of  the  liquid  changing  from  red  to  deep  green.  A  slight  excess  of 
ammonia  precipitates  the  hydrate  from  this  solution.  It  has  a  pale  purplish- 
green  colour,  which  becomes  full  green  on  ignition ;  an  extraordinary  shrink- 
ing of  volume  and  sudden  incandescence  is  observed  when  the  hydrate  is 
decomposed  by  heat.  Anhydrous  sesquioxide  in  a  beautifully  crystalline 
condition  may  be  prepared  by  heating  to  full  redness  in  an  earthen  crucible 
bichromate  of  potassa.  One-half  of  the  acid  sufi"ers  decomposition,  oxygen 
being  disengaged,  and  oxide  of  chromium  left.  The  melted  mass  is  then 
treated  with  water,  which  dissolves  out  neutral  chromate  of  potassa,  and 
the  oxide  is,  lastly,  washed  and  dried.  Sesquioxide  of  chromium  commu- 
nieates  a  fine  green  tint  to  glass,  and  is  used  in  enamel-painting. 

The  sesquioxide  of  chromium  is  a  feeble  base,  resembling,  and  isomor- 
phous  with,  sesquioxide  of  iron  and  alumina  ;  the  salts  it  foi^ms  have  a  green 
or  purple  colour,  and  are  said  to  be  poisonous. 

The  sulphate  of  sesquioxide  of  chromium  is  prepared  by  dissolving  the 
hydrated  oxide  in  dilute  sulphuric  acid.     It  unites  with  the  sulphates  of  po- 


268  CHROMIUM. 

tassa  and  of  ammonia,  giving  rise  to  magnificent  salts  which  crystallize  in 
regular  octahedrons  of  a  deep  claret  colour,  and  possess  a  constitution  re- 
sembling that  of  common  alum,  the  alumina  being  replaced  by  sesquioxide 
of  chromium.  The  finest  crystals  of  chromium-alum  are  obtained  by  spon- 
taneous evaporation,  the  solution  being  apt  to  be  decomposed  by  heat. 

Protochloride  of  chromium,  CrCl. — The  violet-coloured  sesquichloride 
of  chromium,  contained  in  a  porcelain  or  glass  tube,  is  heated  to  redness  in 
a  current  of  perfectly  dry  and  pure  hydrogen  gas ;  hydrochloric  acid  is  dis- 
engaged, and  a  white  foliated  mass  is  obtained,  which  dissolves  in  water 
with  great  elevation  of  temperature,  yielding  a  blue  solution,  which,  by  ex- 
posure to  the  air,  absorbs  oxygen  with  extraordinary  energy,  acquiring  a 
deep  green  colour,  and  passing  into  the  state  of  oxychloride  of  chromium, 
2Cr2Cl3,  CrjOg.  The  protochloride  of  chromium  is  one  of  the  most  powerful 
reducing  or  deoxidizing  agents  known. 

Sesquichloride  of  chromium,  Cr^Clg. — This  substance  is  readily  obtained 
in  the  anhydrous  condition  by  heating  to  redness  in  a  porcelain  tube  a  mix- 
ture of  sesquioxide  of  chromium  and  charcoal,  and  passing  dry  chlorine  gas 
over  it.  The  sesquichloride  sublimes,  and  is  deposited  in  the  cool  part  of 
the  tube,  in  the  form  of  beautiful  crystalline  plates  of  a  pale  violet  colour. 
According  to  M.  P^ligot,  it  is  totally  insoluble  in  water  under  ordinary  cir- 
cumstances, even  at  a  boiling  heat.  It  dissolves,  however,  and  assumes  the 
deep  green  hydrated  state  in  water  containing  an  exceedingly  minute  quan- 
tity of  the  protochloride  in  solution.  The  hydration  is  marked  by  the  evo- 
lution of  much  heat.  This  remarkable  eflFect  must  probably  be  referred  to 
the  class  of  actions  known  at  present  under  the  name  of  katalysis.' 


The  salts  of  the  sesquioxide  of  chromium  are  easily  recognized. 

Caustic  alkalis  precipitate  the  hydrated  oxide,  easily  soluble  in  excess. 

Ammonia,  the  same,  but  nearly  insoluble. 

Carbonates  of  potassa,  soda,  and  ammonia,  throw  down  a  green  precipitate 
of  carbonate  and  hydrate,  slightly  soluble  in  a  large  excess. 

Sulphuretted  hydrogen  causes  no  change. 

Sulphide  of  ammonium  precipitates  the  hydrate  of  the  sesquioxide. 

Chromic  acid,  CrOj. — Whenever  sesquioxide  of  chromium  is  strongly 
heated  with  an  alkali,  in  contact  with  the  air,  oxygen  is  absorbed  and 
chromic  acid  generated.  Chromic  acid  may  be  obtained  nearly  pure,  and  in 
a  state  of  great  beauty,  by  the  following  simple  process :  — 100  measures  of 
a  cold  saturated  solution  of  bichromate  of  potassa  are  mixed  with  150 
measures  of  oil  of  vitriol,  and  the  whole  suffered  to  cool;  the  chromic  acid 
crystallizes  in  brilliant  crimson-red  prisms.  The  mother-liquor  is  poured 
off,  and  the  crystals  placed  upon  a  tile  to  drain,  being  closely  covered  by  a 
glass  or  bell-jar.*  Chromic  acid  is  very  deliquescent  and  soluble  in  water ; 
the  solution  is  instantly  reduced  by  contact  with  organic  matter. 

Ghromate  of  Potassa,  KO,CrOs. — This  is  the  source  of  all  the  preparations 
of  chromium  ;  it  is  made  directly  from  the  native  chrome-iron  ore,  which  is  a 
compound  of  the  sesquioxide  of  chromium  and  protoxide  of  iron,  analogous 
to  magnetic  iron  ore,  by  calcination  with  nitre  or  with  carbonate  of  potassa, 
'■he  stone  being  reduced  to  powder,  and  heated  for  a  long  time  with  the 
alkali  in  a  reverberatory  furnace.  The  product,  when  treated  with  water, 
yields  a  yellow  solution,  which  by  evaporation  deposits  anhydrous  crystals 
of  the  same  colour,  isomorphous  with  sulphate  of  potassa.  Chromate  of 
potassa  has  a  cool,  bitter,  and  disagreeable  taste,  and  dissolves  in  2  parts  of 
water  at  60°  (15°-5C). 

•  See  page  186. 

"  Mr.  Warrington ;  Proceedings  of  Chem.  Soc.  i.  18. 


NICKEL.  269 

Bichromate  of  Potassa,  KO^zCrOg^  —  When  sulphuric  acid  is  added  to  the 
preceding  salt  in  moderate  quantity,  one-half  of  the  base  is  removed,  and 
the  neutral  chromate  converted  into  bichromate.  The  new  salt,  of  which 
immense  quantities  are  manufactured  for  use  in  the  arts,  crystallizes  by  slow 
evaporation  in  beautiful  red  tabular  crystals,  derived  from  an  oblique  rhombic 
prism.  It  melts  when  heated,  and  is  soluble  in  10  parts  of  water,  and  the 
solution  has  an  acid  reaction. 

Chromate  of  Lead,  PbO,CrOs. — On  mixing  solution  of  chromate  or  bichro- 
mate of  potassa  with  nitrate  or  acetate  of  lead,  a  brilliant  yellow  precipitate 
falls,  which  is  the  compound  in  question;  it  is  the  chrome-yeUow  of  the 
painter.  When  this  compound  is  boiled  with  lime-water,  one-half  of  the 
acid  is  withdrawn,  and  a  subchromate  of  an  oi'ange-red  colour  left.  The 
subchromate  is  also  formed  by  adding  chromate  of  lead  to  fused  nitre,  and 
afterwards  dissolving  out  the  soluble  salts  by  water ;  the  product  is  crystal- 
line, and  rivals  vermilion  in  beauty  of  tint.  The  yellow  and  orange  chrome - 
colours  are  fixed  upon  cloth  by  the  alternate  application  of  the  two  solutions, 
and  in  the  latter  case  by  passing  the  dyed  stuff  through  a  bath  of  boiling 
lime-water. 

Chromate  of  Silver,  AgO.CrOj!  —  This  salt  precipitates  as  a  reddish  brown 
powder  when  solutions  of  chromate  of  potassa  and  nitrate  of  silver  are 
mixed.  It  dissolves  in  hot  dilute  nitric  acid,  and  separates,  on  cooling,  in 
small  ruby-red  platy  crystals.  The  chromates  of  bai-yta,  zinc,  and  mercury 
are  insoluble ;  the  first  two  are  yellow,  the  last  is  brick-red. 

Perchromic  Acid  is  obtained,  according  to  Barreswill,  by  mixing  chromic 
acid  with  dilute  binoxide  of  hydrogen  or  bichromate  of  potassa  with  a  dilute 
but  very  acid  solution  of  binoxide  of  barium  in  hydrochloric  acid,  when  a 
liquid  is  formed  of  a  blue  colour,  which  is  removed  from  the  aqueous 
solution  by  ether.  The  composition  of  this  very  unstable  compound  is  per- 
haps Cr^O^. 

A  salt  of  chromic  acid  is  at  once  recognised  by  its  behaviour  with  solu- 
tions of  baryta  and  lead  ;  and  also  by  its  colour  and  capability  of  furnishing, 
by  deoxidation,  the  green  sesquioxide  of  chromium. 


Chlorochromic  acid,  CrOg-f-Cl." — 3  parts  of  bichromate  of  potassa  and 
3^  parts  of  common  salt  are  intimately  mixed  and  introduced  mia  a  small 
glass  retort ;  9  parts  of  oil  of  vitriol  are  then  added,  and  heat  applied  as 
long  as  dense  red  vapours  arise.  The  product  is  a  heavy  deep  red  liquid 
resembling  bromine  ;  it  is  decomposed  by  water,  with  production  of  chromic 
and  hydrochloric  acids. 

Nickel. 

Nickel  is  found  in  tolerable  abundance  in  some  of  the  metal-bearing  veins 
of  the  Hartz  mountains,  and  in  a  few  other  localities,  chiefly  as  arsenide,  the 
kupfernickel  of  mineralogists,  so  called  from  its  yellowish-red  colour;  the 
word  nickel  is  a  term  of  detraction,  having  been  applied  by  the  old  German 
miners  to  what  was  looked  upon  as  a  kind  of  false  copper  ore. 

The  artificial,  or  perhaps  rather  merely  fused,  product,  called  speiss,  ia 
nearly  the  same  substance,  and  may  be  employed  as  a  source  of  the  nickel- 
salts.     This  metal  is  found  in  meteoric  iron,  as  already  mentioned. 

Nickel  is  easily  prepared  by  exposing  the  oxalate  to  a  high  white  heat,  m 

» If  this  formula  be  trebled,  we  obtain  Cr30eCl3=2CrOa,CrC:i3,  and  the  substance  becomes  a 
compound  of  2  eq.  of  chromic  acid  aud  1  eq.  of  terchloride  of  chromium.     The  terchloride  of 
chromium  is  not  known  in  the  free  state. 
23  ♦ 


270  NICKEL. 

a  crucible  lined  with  charcoal.  It  is  a  white,  malleable  metal,  having  a  den- 
sity of  8-8,  a  high  melting  point,  and  a  less  degree  of  oxidability  than  iron, 
since  it  is  but  little  attacked  by  dilute  acids.  Nickel  is  strongly  magnetic, 
but  loses  this  property  when  heated  to  660°  (349°C).  This  metal  forms  two 
oxides,  only  one  of  which  is  basic.  The  equivalent  of  nickel  is  29-6;  its 
symbol  is  Ni. 

Protoxide  op  nickel,  NiO.  —  This  compound  is  prepared  by  heating  to 
redness  the  nitrate,  or  by  precipitating  a  soluble  salt  with  caustic  potassa, 
and  washing,  drying,  and  igniting  the  apple-green  hydrated  oxide  thrown 
down.  ^  It  is  an  ash-grey  powder,  freely  soluble  in  acids,  which  it  completely 
neutralizes,  being  isomorphous  with  magnesia,  and  the  other  members  of  the 
same  group.  The  salts  of  this  substance,  when  hydrated,  have  usually  a 
beautiful  green  colour ;  in  the  anhydrous  state  they  are  yellow. 

Sesquioxide,  or  peroxide  of  nickel,  NijOg.  —  This  oxide  is  a  black  in- 
soluble substance,  prepared  by  passing  chlorine  through  the  hydrated  oxide 
suspended  in  water;  chloride  of  nickel  is  formed,  and  the  oxygen  of  the 
oxide  decomposed  transferred  to  a  second  portion.  It  is  also  produced  when 
a  salt  of  nickel  is  mixed  with  a  solution  of  bleaching-powder.  The  sesqui- 
oxide is  decomposed  by  heat,  and  evolves  chlorine  when  put  into  hot  hydro- 
chloric acid. 

Chloride  op  nickel,  NiCl.  —  This  is  easily  prepared  by  dissolving  oxide 
or  carbonate  of  nickel  in  hydrochloric  acid,  A  green  solution  is  obtained 
which  furnishes  crystals  of  the  same  colour,  containing  water.  When  ren- 
dered anhydrous  by  heat,  the  chloride  is  yellow,  unless  it  contain  cobalt,  in 
which  case  it  has  a  tint  of  green. 

Sulphate  of  nickel,  NiO,S03-|-7HO. — This  is  the  most  important  of  the 
salts  of  nickel.  It  forms  green  prismatic  crystals,  containing  7  equivalents 
of  water,  which  require  3  parts  of  cold  water  for  solution.  Crystals  with  6 
equivalents  of  water  have  also  been  obtained.  It  forms  with  the  sulphates 
of  potassa  and  ammonia  beautiful  double  salts,  NiO,S03  -f  KOjSOg  -f  6H0 
and  NiO,S03  -f-  NH^O,  SOg-f  6H0.  When  a  strong  solution  of  oxalic  acid 
is  mixed  with  sulphate  of  nickel,  a  pale  bluish-green  precipitate  of  oxalate 
falls  after  some  time,  very  little  nickel  remaining  in  solution.  The  oxalate 
can  thus  be  obtained  for  preparing  the  metal. 

Carbonate  of  nickel. — When  solutions  of  sulphate  or  chloride  of  nickel 
and  of  carbonate  of  soda  are  mixed,  a  pale  green  precipitate  falls,  which  is 
a  combination  of  carbonate  and  hydrate  of  nickel.  It  is  readily  decomposed 
by  heat. 

Pure  salts  of  nickel  are  conveniently  prepared  on  the  small  scale  from 
crude  speiss  or  kupfernickel  by  the  following  process :  —  The  mineral  is 
broken  into  small  fragments,  mixed  with  from  one-fourth  to  half  its  weight 
of  iron-filings,  and  the  whole  dissolved  in  aqua  regia.  The  solution  is  gently 
evaporated  to  dryness,  the  residue  treated  with  boiling  water,  and  the  inso- 
luble arsenate  of  iron  removed  by  a  filter.  The  liquid  is  then  acidulated 
with  hydrochloric  acid,  treated  with  sulphuretted  hydrogen  in  excess,  which 
precipitates  the  copper,  and,  after  filtration,  boiled  with  a  little  nitric  acid  to 
bring  back  the  iron  to  the  state  of  sesquioxide.  To  the  cold  and  largely 
diluted  liquid,  solution  of  bicarbonate  of  soda  is  gradually  added,  by  which 
the  sesquioxide  of  iron  may  be  completely  separated  without  loss  of  nickel- 
salt.  Lastly,  the  filtered  solution,  boiled  with  carbonate  of  soda  in  excess, 
yields  an  abundant  pale  green  precipitate  of  carbonate  of  nickel,*  from  which 
all  the  other  compounds  may  be  prepared. 

»  This  precipitate  may  still  contain  cobalt,  which  can  only  be  separated  from  it  by  very 
implicated  processes,  for  which  the  more  advanced  student  is  referred  to  "Liebig  and  Kopp's 
J^flfii^W  Report,"  ji.  334, 


COBALT.  271 

The  salts  of  iiickol  are  well  characterized  by  th«ir  behaviour  "with  re- 
agents. 

Caustic  alkalis  give  a  pale  apple-green  precipitate  of  hydrate,  insoluble  in 
excess. 

Ammonia  affords  a  similar  precipitate,  -which  is  soluble  in  excess,  with 
deep  purplish-blue  colour. 

Carbouate  of  potassa  and  soda  give  pale  green  precipitates. 

Carbonate  of  ammonia,  a  similar  precipitate,  soluble  in  excess,  with  blue 
colour. 

Ferrocyanide  of  potassium  gives  a  greenish-white  precipitate. 

Cyanide  of  potassium  produces  a  green  precipitate,  which  dissolves  in  an 
excess  of  the  precipitant  to  an  amber-coloured  liquid  which  is  re-precipitated 
by  addition  of  hydrochloric  acid. 

Sulphuretted  hydrogen  occasions  no  change,  if  the  nickel  be  in  combina- 
tion with  a  strong  acid. 

Sulphide  of  ammonium  throws  down  black  sulphide  of  nickel. 


The  chief  use  of  nickel  in  the  arts  is  in  the  preparation  of  a  white  alloy, 
sometimes  called  German  silver,  made  by  melting  together  100  parts  of 
copper,  60  of  zinc,  and  40  of  nickel.  This  alloy  is  very  malleable,  and  takes 
a  high  polish. 

COBALT. 

This  substance  bears,  in  many  respects,  an  extraordinary  resemblance  to 
the  metal  last  described ;  it  is  often  associated  with  it  in  nature,  and  may 
be  obtained  from  its  compounds  by  similar  means.  Cobalt  is  a  white,  brittle 
metal,  having  a  specific  gravity  of  8-5,  and  a  very  high  melting  point.  It 
is  unchanged  in  the  air,  and  but  feebly  attacked  by  dilute  hodrochloric 
and  sulphuric  acids.  It  is  strongly  magnetic.  There  are  two  oxides  of 
this  metal,  corresponding  in  properties  and  constitution  with  those  of 
nickel. 

The  equivalent  of  cobalt  is  29-.5-5  :  its  symbol  is  Co. 

Protoxide  of  cobalt,  CoO. — This  is  a  grey  powder,  very  soluble  in  acids, 
and  is  a  strong  base,  isomorphous  with  magnesia,  affording  salts  of  a  fine 
red  tint.  It  is  prepared  by  precipitating  sulphate  or  chloride  of  cobalt  with 
carbonate  of  soda,  and  washing  and  drying  and  igniting  the  precipitate. 
When  the  cobalt-solution  is  mixed  with  caustic  potassa  a  beautiful  blue  pre 
cipitate  falls,  which  when  heated  becomes  violet,  and  at  length  dirty  red, 
from  absorption  of  oxygen  and  a  change  in  the  state  of  hydration. 

yKSQuioxiuE  OF  COBALT,  COgOg. — The  sesquioxide  is  a  black,  insoluble, 
neutral  powder,  obtained  by  mixing  solutions  of  cobalt  and  of  chloride  of 
lime. 

( 'hloride  of  COBALT,  CoCl.  —  The  chloride  is  easily  prepared  by  dissolving 
the  oxide  in  hydrochloric  acid;  it  gives  a  deep  rose- red  solution,  which, 
when  suificiently  strong,  deposits  hydrated  crystals  of  the  same  colour. 
When  the  liijuid  is  evaporated  by  heat  to  a  very  small  bulk,  it  deposits  anhy- 
drous crystals  which  are  blue ;  these  latter  by  contact  with  water  again 
dissolve  to  a  red  liquid.  A  dilute  solution  of  chloride  of  cobalt  constitutes 
the  well'known  blue  sympathetic  ink  ;  characters  written  on  paper  with  this 
liquid  are  invisible  from  their  paleness  of  colour  until  the  salt  has  been 
rendered  anhydrous  by  exposure  to  heat,  when  the  letters  appear  blue. 
When  laid  aside,  moisture  is  absorbed,  and  the  writing  once  more  dis- 
appears. Green  sympathetic  ink  is  a  mixture  of  the  chlorides  of  cobalt  and 
mckel. 


272  ZINC. 


walt-c 


Chloride  of  coLalt  may  be  prepared  directly  from  cobalt- ff lance,  the  native 
arsenide,  by  a  process  exactly  similar  to  that  described  in  the  case  of  nickel. 

Sulphate  of  cobalt,  CoO,S03-f-7HO. — This  salt  forms  deep  red  crystals, 
requiring  for  solution  24  parts  of  cold  water;  they  are  identical  in  form 
•with  those  of  sulphate  of  magnesia.  It  combines  with  the  sulphates  of  po- 
tassa  and  ammonia,  forming  double  salts,  which  contain  as  usual  six  equiva- 
lents of  water. 

A  solution  of  oxalic  acid  added  to  one  of  sulphate  of  cobalt  occasions, 
after  some  time,  the  separation  of  nearly  the  whole  of  the  base  in  the  state 
of  oxalate. 

Carbonate  of  cobalt.  —  The  alkaline  carbonates  produce  in  solution  of 
cobalt  a  pale  peach-blossom  coloured  precipitate  of  combined  carbonate  and 
hydrate,  containing  3(CoO,HO)-f2(CoOCO,). 


The  salts  of  cobalt  have  the  following  characters : — 

Solution  of  potassa  gives  a  blue  precipitate,  changing  by  heat  to  violet 
and  red. 

Ammonia  gives  a  blue  precipitate,  soluble  with  difficulty  in  excess,  with 
brownish  red  colour. 

Carbonate  of  soda  affords  a  pink  precipitate. 

Carbonate  of  ammonia,  a  similar  compound,  soluble  in  excess. 

Ferrocyanide  of  potassium  gives  a  greyish-green  precipitate. 

Cyanide  of  potassium  affords  a  yellowish-brown  precipitate,  which  dissolves 
In  an  excess  of  the  precipitant.  The  clear  solutions,  after  boiling,  may  be 
mixed  with  hydrochloric  acid  without  giving  a  precipitate. 

Sulphuretted  hydrogen  produces  no  change,  if  the  cobalt  be  in  combination 
with  a  strong  acid. 

Sulphide  of  ammonium  throws  down  black  sulphide  of  cobalt. 


Oxide  of  cobalt  is  remarkable  for  the  magnificent  blue  colour  it  communi- 
cates to  glass :  indeed  this  is  a  character  by  which  its  presence  may  be  most 
easily  detected,  a  very  small  portion  of  the  substance  to  be  examined  being 
fused  with  borax  on  a  loop  of  platinum  wire  before  the  blowpipe.  The  sub- 
stance called  smalt,  used  as  a  pigment,  consists  of  glass  coloured  by  oxide  of 
cobalt ;  it  is  thus  made : — The  cobalt  ore  is  roasted  until  nearly  free  from 
arsenic,  and  then  fused  with  a  mixture  of  carbonate  of  potassa  and  quartz- 
sand,  free  from  oxide  of  iron.  Any  nickel  that  may  happen  to  be- contained 
in  the  ore  then  subsides  to  the  bottom  of  the  crucible  as  arsenide ;  this  is 
the  speiss  of  which  mention  has  already  been  made.  The  glass,  when  com- 
plete, is  removed  and  poured  into  cold  water ;  it  is  afterwards  ground  to 
powder  and  elutriated.  Cobalt-ultramarine  is  a  fine  blue  colour  prepared  by 
mixing  16  parts  of  freshly  precipitated  alumina  with  2  parts  of  phosphate  or 
arsenate  of  cobalt :  this  mixture  is  dried  and  slowly  heated  to  redness.  By 
daylight  the  colour  is  pure  blue,  but  by  artificial  light  it  is  violet.  Zaffer  is 
the  roasted  cobalt  ore  mixed  with  a  quantity  of  siliceous  sand,  and  reduced 
to  fine  powder;  it  is  used  in  enamel-painting.  A  mixture  in  due  proportions 
of  the  oxides  of  cobalt,  manganese,  and  iron  is  used  for  giving  a  fine  black 
colour  to  glass. 


Zinc  is  a  somewhat  abundant  metal ;  it  is  found  in  the  state  of  carbonate 
and  sulphide  associated  with  lead  ores  in  many  districts,  both  in  Britain  and 


ZINC.  ^273 

on  the  Continent ;  large  supplies  are  obtained  from  Silesia.  The  native  car- 
bonate, or  calamine,  is  the  most  valuable  of  the  zinc  ores,  and  is  preferred 
for  the  extraction  of  the  metal ;  it  is  first  roasted  to  expel  water  and  carbonic 
acid,  mixed  with  fragments  of  coke  or  charcoal,  and  then  distilled  at  a  full 
red-heat  in  a  large  earthen  retort ;  carbonic  oxide  escapes,  while  the  reduced 
metal  volatilizes  and  is  condensed  by  suitable  means,  generally  with  minute 
quantities  of  arsenic. 

Zinc  is  a  bluish-white  metal,  which  slowly  tarnishes  in  the  air ;  it  has  a 
lamellar,  crystalline  structure,  a  density  varying  from  6-8  to  7-2,  and  is, 
under  ordinary  circumstances,  brittle.  Between  250°  (121°C)  and  300° 
(149°C)  it  is,  on  the  contrary,  malleable,  and  may  be  rolled  or  hammered 
without  danger  of  fracture,  and,  what  is  very  remarkable,  after  such  treat- 
ment, retains  it  malleability  when  cold :  the  sheet-zinc  of  commerce  is  thus 
made.  At  400°  (204° -40)  it  is  so  brittle  that  it  may  be  reduced  to  powder. 
At  773°  (411°-GC)  it  melts :  at  a  bright  red-heat  it  boils  and  volatilizes,  and, 
if  air,  be  admitted,  burns  with  a  splendid  green  light,  generating  the  oxide. 
Dilute  acids  dissolve  zinc  very  readily;  it  is  constantly  employed  in  this 
manner  in  preparing  hydrogen  gas. 

The  equivalent  of  zinc  has  been  fixed  at  32-6;  its  symbol  is  Zn. 

Protoxide  of  zinc,  ZnO. — Only  one  oxide  of  this  metal  is  known  to 
exist ;  it  is  a  strong  base,  isomorphous  with  magnesia ;  it  is  prepared  either 
by  burning  zinc  in  atmospheric  air,  or  by  heating  to  redness  the  carbonate. 
Oxide  of  zinc  is  a  white  tasteless  powder,  insoluble  in  water,  but  freely  dis- 
solved by  acids.    When  heated  it  is  yellow,  but  turns  white  again  on  cooling. 

Sulphate  of  zinc  ;  white  vitriol;  ZnO,  SO3-J-7HO.  This  salt  is  hardly 
to  be  distinguished  by  the  eye  from  the  sulphate  of  magnesia ;  it  is  pre- 
pared by  dissolving  the  metal  in  dilute  sulphuric  acid,  or,  more  economically, 
by  roasting  the  native  sulphide,  or  blende,  which  by  absorption  of  oxygen 
becomes  in  great  part  converted  into  sulphate  of  the  oxide.  The  altered 
mineral  is  thrown  hot  into  water,  and  the  salt  obtained  by  evaporating  the 
clear  solution.  Sulphate  of  zinc  has  an  astringent  metallic  taste,  and  is 
used  in  medicine  as  an  emetic.  The  crystals  dissolve  in  2^  parts  of  cold, 
and  in  a  much  smaller  quantity  of  hot  water.  Crystals  containing  6  equiva- 
lents of  water  have  been  observed.  Sulphate  of  zinc  forms  double  salts 
with  the  sulphates  of  potassa  and  ammonia. 

Carbonate  of  zinc,  ZuOjCOj.  —  The  neutral  carbonate  is  found  native ; 
the  white  precipitate  obtained  by  mixing  solutions  of  zinc  and  of  alkaline 
carbonates  is  a  combination  of  carbonate  and  hydrate.  When  heated  to 
redness,  it  yields  pure  oxide  of  zinc. 

Chloride  of  zinc,  ZnCl.  —  The  chloride  may  be  prepared  by  heating 
metallic  zinc  in  chlorine ;  by  distilling  a  mixture  of  zinc-filings  and  corrosive 
sublimate  ;  or,  more  easily,  by  dissolving  zinc  in  hydrochloric  acid.  It  is  a 
nearly  white,  translucent,  fusible  substance,  very  soluble  in  water  and 
alcohol,  and  very  deliquescent.  A  strong  solution  of  chloride  of  zinc  is 
sometimes  used  as  a  bath  for  obtaining  a  graduated  heat  above  212° 
(100°C).  Chloride  of  zinc  unites  with  sal-ammoniac  and  chloride  of  potas- 
sium to  double  salts  ;  the  former  of  these,  made  by  dissolving  an  equivalent 
of  zinc  in  the  requisite  quantity  of  hydrochloric  acid,  and  then  adding  an 
equivalent  of  sal-ammoniac,  is  very  useful  in  tinning  and  soft-soldering 
copper  and  iron. 

A  salt  of  zinc  is  easily  distinguished  by  appropriate  reagents.        ♦ 
Caustic  potassa  and  soda  give  a  white  precipitate  of  hydrate,  freely  soluble 

in  excess  of  alkali. 

Ammonia  behaves  in  the  same  manner ;  an  excess  re  dissolves  the  precipi 

tate  instantly. 


274  CADMIUM  —  BISMUTH. 

The  carbonates  of  potassa  and  soda  give  white  precipitates,  insoluble  in 
excess. 

Carbonate  of  ammonia  gives  also  a  white  precipitate,  which  is  re-dissolved 
by  an  excess. 

Ferrocyauide  of  potassium  gives  a  white  precipitate. 

Sulphuretted  hydi'ogen  causes  no  change.* 

Sulphide  of  ammonium  throws  down  white  sulphide  of  zinc. 


The  applications  of  metallic  zinc  to  the  purposes  of  roofing,  the  construc- 
tion of  water-channels,  &c.,  are  well  known;  it  is  sufficiently  durable,  but 
inferior  in  this  respect  to  copper. 


This  metal  was  discovered  in  1817  by  Stromeyer ;  it  accompanies  the  ores 
of  zinc,  and,  being  more  volatile  than  that  substance,  rises  first  in  vapour 
when  the  calamine  is  subjected  to  distillation  with  charcoal.  Cadmium 
resembles  tin  in  colour,  but  is  somewhat  harder ;  it  is  very  malleable,  has 
a  density  of  8-7,  melts  below  500°  (260°C),  and  is  nearly  as  volatile  as  mer- 
cury. It  tarnishes  but  little  in  the  air,  but,  when  strongly  heated,  burns. 
Dilute  sulphuric  and  hydrochloric  acids  act  but  little  on  this  metal  in  the 
cold  ;  nitric  acid  is  its  best  solvent. 

The  equivalent  of  cadmium  is  56  ;  its  symbol  is  Cd. 

Protoxide  of  cadmium,  CdO.  —  The  oxide  may  be  prepared  by  igniting 
either  the  carbonate  or  the  nitrate ;  in  the  former  case  it  has  a  pale  brown 
colour,  and  in  the  latter  a  much  darker  tint  and  a  crystalline  aspect.  Oxide 
of  cadmium  is  infusible ;  it  dissolves  in  acids,  producing  a  series  of  colourless 
salts. 

Sulphate  of  cadmium,  CdO,S03-f-4HO.  —  This  is  easily  obtained  by  dis- 
solving the  oxide  or  carbonate  in  dilute  sulphuric  acid ;  it  is  very  soluble  in 
water,  and  forms  double  salts  with  the  sulphates  of  potassa  and  of  ammonia, 
which  contain  CdO,S03-(-KO,SOg-f6HO,  and  CdO,S034  NH^CSOg-j-eHO. 

Chloride  of  cadmium,  CdCl.  —  This  is  a  very  soluble  salt,  crystallizing  in 
small  four-sided  prisms. 

Sulphide  of  cadmium  is  a  very  characteristic  compound,  of  a  bright  yellow 
colour,  fusible  at  a  high  temperature.  It  is  obtained  by  passing  sulphuretted 
hydrogen  gas  through  a  solution  of  the  sulphate,  nitrate,  or  chloride. 


The  salts  of  cadmium  are  thus  distinguished  : — 

Fixed  caustic  alkalis  give  a  white  precipitate  of  hydrated  oxide,  insoluble 
in  excess. 

Ammonia  gives  a  similar  white  precipitate,  readily  soluble  in  excess. 

The  alkaline  carbonates,  and  carbonate  of  ammonia,  throw  down  white 
carbonate  of  cadmium,  insoluble  in  excess  of  either  precipitant. 

Sulphuretted  hydrogen  and  sulphide  of  ammonium  precipitate  the  yellow 
sulphide  of  cadmium. 

BISMUTH. 

Bismuth  is  found  chiefly  in  the  metallic  state,  disseminated  through  an 
earthy  matrix,  from  which  it  is  separated  by  simple  exposure  to  heat.  The 
metal  is  highly  crj'stalline  and  very  brittle;  it  has  a  reddish-white  colour, 
and  a  density  of  9-9.     Cubic  crystals  of  great  beauty  may  be  obtained  by 

'  With  neutral  solutions,  or  zine-salts  of  an  organic  acid,  a  white  precipitate  ensues. 


BISMUTH.  275 

slowly  cooliug  a  considerable  mass  of  this  substance  until  solidification  has 
commenced,  and  then  piercing  the  crust,  and  pouring  out  the  tiuid  residue. 
Bismuth  melts  at  about  500°  (260°C),  and  volatilizes  at  a  high  temperature : 
it  is  little  oxidized  by  the  air,  but  burns  when  strongly  heated  with  a  bluish 
flame.     Nitric  acid,  somewhat  diluted,  dissolves  it  freely. 

The  equivalent  of  bismuth  is  213,  its  symbol  is  Bi. 

Teroxiue  of  bismuth,  Bi03.  —  This  is  the  base  of  all  the  salts.  It  is  a 
straw-yellow  powder,  obtained  by  gently  igniting  the  neutral  or  basic  nitrate. 
It  is  fusible  at  a  high  temperature,  and  in  that  state  acts  towards  siliceous 
matter  as  a  powerful  flux. 

BisMUTHic  ACID,  BiOj.  —  If  teroxide  of  bismuth  be  suspended  in  a  strong 
solution  of  potassa,  and  chlorine  be  passed  through  this  liquid,  decomposition 
of  water  ensues ;  hydrochloric  acid  being  formed  and  the  teroxide  converted 
into  the  pentoxide.  To  separate  any  teroxide  which  maj'  have  escaped  oxi- 
dation, the  powder  is  treated  with  dilute  nitric  acid,  when  the  bismuthic 
acid  is  left  as  a  reddish  powder,  which  is  insoluble  in  water.  This  substance 
combines  with  bases,  but  the  compounds  are  not  very  well  known.  When 
heated  it  loses  oxygen,  an  intermediate  oxide  Bi04  being  formed,  which  may 
be  considered  as  bismuthate  of  bismuth,  2Bi04=Bi03,Bi05. 

Nitrate  of  bismuth,  Bi03,N05-f-9H0.  — When  bismuth  is  dissolved  in 
moderately  strong  nitric  acid  to  saturation,  and  the  whole  left  to  cool,  large, 
colourless,  transparent  crystals  of  the  neutral  nitrate  are  deposited.  Water 
decomposes  these  crystals;  and  an  acid  solution  containing  a  little  bismuth 
is  obtained,  and  a  brilliant  white  crystalline  powder  is  left,  which  varies  to 
a  certain  extent  in  composition  according  to  the  temperature  and  the  quan- 
tity of  water  employed,  but  which  frequently  consists  of  a  basic  nitrate  of 
the  teroxide  BiOa.SNOg-f-^HO.  A  solution  of  nitrate  of  bismuth,  free  from 
any  great  excess  of  acid,  poured  into  a  large  quantity  of  cold  water,  yields 
an  insoluble  basic  nitrate,  very  similar  in  appearance  to  the  above,  but  con- 
taining rather  a  larger  proportion  of  teroxide  of  bismuth.  This  remarkable 
decomposition  illustrates  at  once  the  basic  property  of  water,  and  the  feeble 
aftinity  of  teroxide  of  bismuth  for  acids,  the  nitric  acid  dividing  itself  between 
the  two  bases.  The  decomposition  of  a  neutral  salt  by  water  iS  by  no  means 
an  uncommon  occurrence  in  the  history  of  the  metals ;  a  solution  of  terchlo- 
ride  of  antimony  exhibits  the  same  phenomenon ;  certain  salts  of  mercury 
are  affected  in  a  similar  manner,  and  other  cases  might  perhaps  be  cited,  less 
conspicuous,  where  the  same  change  takes  place  to  a  smaller  extent. 

The  basic  nitrate  of  teroxide  of  bismuth  was  once  extensively  employed  a» 
a  cosmetic,  but  is  said  to  injure  the  skin,  rendering  it  yellow  and  leather-like. 
It  has  been  used  in  medicine. 

The  other  salts  of  bismuth  possess  few  points  of  interest. 


Bismuth  is  sufliciently  characterized  by  the  decomposition  of  the  nitrate 
by  water,  and  by  the  blackening  the  nitrate  undergoes  when  exposed  to  the 
action  of  sulphuretted  hydrogen  gas. 

A  mixture  of  8  parts  of  bismuth,  5  parts  of  lead,  and  3  of  tin,  is  known 
■nnder  the  name  of  fusible  metal,  and  is  employed  in  taking  impressions  from~ 
dies  and  for  other  purposes;  it  melts  below  212°  (100°C).  The  discrepan- 
cies so  frequently  observed  between  the  properties  of  alloys  and  those  of 
their  constituent  metals,  plainly  show  that  such  substances  must  be  lookea 
upon  as  true  chemical  compounds,  and  not  as  mere  mixtures ;  in  the  present 
case  the  proof  is  complete,  for  the  fusible  metal  has  lately  been  obtained  in 
crystals. 


276  URANIUM. 


URANIUM. 

This  metal  is  found  in  a  few  minerals,  as  pitchblende  and  uranite,  of  which 
the  former  is  the  most  abundant.  It  appears  from  the  recent  interesting  re- 
searches of  M.  P61igot,  that  the  substance  hitherto  taken  for  metallic  ura- 
nium, obtained  by  the  action  of  hydrogen  gas  upon  the  black  oxide,  is  no^ 
in  reality  the  metal,  but  a  protoxide,  capable  of  uniting  directly  with  acids, 
and,  like  the  protoxide  of  manganese,  not  decomposable  by  hydrogen  at  a 
red-heat.  The  metal  itself  can  be  obtained  only  by  the  intervention  of  po 
tassium,  applied  in  the  same  manner  as  in  the  preparation  of  magnesium. 
It  is  described  as  a  black  coherent  powder,  or  a  white  malleable  metal,  ac- 
cording to  the  state  of  aggregation,  not  oxidized  by  air  or  water,  but  emi- 
nently combustible  when  exposed  to  heat.  It  unites  also  with  great  violence 
with  chlorine  and  with  sulphur.  M.  P61igot  admits  three  distinct  oxides  of 
uranium,  besides  two  other  compounds  of  the  metal  and  oxygen,  which  he 
designates  as  suboxides. 

The  equivalent  of  uranium  is  60.     Its  symbol  is  U. 

Protoxide  of  uranium,  UO. — This  is  the  ancient  metal ;  it  is  prepared 
^y  several,  processes,  one  of  which  has  been  already  mentioned.  It  is  a 
brown  powder,  sometimes  highly  crystalline.  When  in  minute  division  it  is 
pyrophoric,  taking  fire  in  the  air,  and  burning  to  black  oxide.  It  forms  with 
acids  a  series  of  green  salts.  A  corresponding  chloride  exists,  which  forms 
dark  green  octahedral  crystals,  highly  deliquescent  and  soluble  in  water. 
M.  Peligot  attributes  a  very  extraordinary  double  function  to  this  substance, 
namely,  that  of  acting  as  a  protoxide  and  forming  salts  with  acids,  and  that 
of  combining  with  chlorine  or  oxygen  after  the  fashion  of  an  elementary 
body. 

Protosesquioxide  of  uranium;  black  oxide;  U4O5,  or  2UO-f-U203. — 
The  black  oxide,  formerly  considered  as  protoxide,  is  produced  when  both 
protoxide  and  sesquioxide  are  strongly  heated  in  the  air,  the  former  gaining, 
and  the  latter  losing,  a  certain  quantity  of  oxygen.  It  forms  no  salts,  but 
is  resolved  by  solution  in  acids  into  protoxide  and  sesquioxide. 

Sesquioxide  of  uranium,  UjOg. — The  sesquioxide  is  the  best  known  and 
most  important  of  the  three ;  it  forms  a  number  of  extremely  beautiful  yel- 
low salts.  When  caustic  alkali  is  added  to  a  solution  of  nitrate  of  sesqui- 
oxide of  uranium,  a  yellow  precipitate  of  hydrated  oxide  falls,  which,  re- 
tains, however,  a  portion  of  the  precipitant.  Thf  hydrate  cannot  be  exposed 
to  a  heat  sufficient  to  expel  the  water  without  a  commencement  of  decompo- 
sition. A  better  method  of  obtaining  the  sesquioxide  is  to  heat  by  means 
of  an  oil-bath  the  powdered  and  dried  crystals  of  the  nitrate  to  480°  (249°C), 
until  no  more  nitrous  fumes  are  disengaged.  Its  colour  in  this  state  is 
chamois-yellow. 

Nitrate  of  sesquioxide  of  uranium,  UjOgjNOg-f-BHO;  or  (Uj^j)  ^'  ^^s 
-}-6H0;  UjOg  being  the  supposed  gMose-meiaZ. — This  nitrate  is  the  starting 
point  in  the  preparation  of  all  the  compounds  of  uranium ;  it  may  be  pre- 
})ared  from  pitchblende  by  dissolving  the  pulverized  mineral  in  nitric  acid, 
evaporating  to  dryness,  adding  water  and  filtering ;  the  liquid  furnishes,  l5y 
clue  evaporation,  crystals  of  nitrate  of  uranium,  which  are  purified  by  a 
repetition  of  the  process,  and,  lastly,  dissolved  in  ether.  This  latter  solu- 
l^on  yields  the  pure  nitrate. 

The  green  salts  of  uranium  are  peroxidized  by  boiling  with  nitric  acid. 


A  yellow  precipitate  with  caustic  alkalis,  convertible  by  heat  into  black 
oxide;  a  brown  precipitate  with  sulphide  of  ammonium;  and  none  at  all 
with  Fulohuietted  hydrogen  gas,  sufficiently  characterize  the  salts  of  sesqui- 


COPPER.  277* 

oxide  of  uranium.     A  solution  suspected  to  contain  m-otoxide  may  be  boiled 
■with  a  little  nitric  acid,  and  then  examined. 


The  only  application  of  uranium  is  that  to  enamel-painting  and  the  stain- 
ing of  glass ;  the  protoxide  giving  a  fine  black  colour,  and  the  sesquioxide 
a  delicate  yellow. 

COPPER. 

Copper  is  a  metal  of  great  value  in  the  arts  of  life ;  it  sometimes  occur 
in  the  metallic  state,  crystallized  in  octahedrons,  but  is  more  abundant  ii 
the  condition  of  red  oxide,  and  in  that  of  sulphide  combined  with  sulphide 
of  iron,  or  yellow  copper  ore.  Large  quantities  of  the  latter  substance  are 
annually  obtained  from  the  Cornish  mines  and  taken  to  South  Wales  for  re- 
duction, which  is  eflected  by  a  somewhat  complex  process.  The  principle 
of  this  may,  however,  be  easily  made  intelligible.  The  ore  is  roasted  in  a 
reverberatory  furnace,  by  which  much  of  the  sulphide  of  iron  is  converted 
into  oxide,  while  the  sulphide  of  copper  remains  unaltered.  The  product 
of  this  operation  is  then  strongly  heated  with  siliceous  sand ;  the  latter 
combines  with  the  oxide  of  iron  to  a  fusible  slag,  and  separates  from  the 
heavier  copper-compound.  When  the  iron  has,  by  a  repetition  of  these  pro- 
cesses been  got  rid  of,  the  sulphide  of  copper  begins  to  decompose  in  the 
flame-furnace,  losing  its  sulphur  and  absorbing  oxygen ;  the  temperature  is 
then  raised  sufficiently  to  reduce  the  oxide  thus  produced,  by  the  aid  of  car- 
bonaceous matter.  The  last  part  of  the  operation  consists  in  thrusting  into 
the  melted  metal  a  pole  of  birch-wood,  the  object  of  which  is  probably  to 
reduce  a  little  remaining  oxide  by  the  combustible  gases  thus  generated. 
Large  quantities  of  extremely  valuable  ore,  chiefly  carbonate  and  red  oxide, 
have  lately  been  obtained  from  South  Australia. 

Copper  has  a  well-known  yellowish-red  colour,  a  specific  gravity  of  8-96, 
and  is  very  malleable  and  ductile ;  it  is  an  excellent  conductor  of  heat  and 
electricity ;  it  melts  at  a  bright  red-heat,  and  seems  to  be  a  little  volatile  at 
a  very  high  temperature.  Copper  undergoes  no  change  in  dry  air;  exposed 
to  a  moist  atmosphere,  it  becomes  covered  with  a  strongly  adherent  green 
crust,  consisting  in  a  great  measure  of  carbonate.  Heated  to  redness  in 
the  air,  it  is  quickly  oxidized,  becoming  covered  with  a  black  scale.  Dilute 
sulphuric  and  hydrochloric  acids  scarcely  act  upon  copper;  boiling  oil  of 
vitriol  attacks  it  with  evolution  of  sulphurous  acid ;  nitric  acid,  even  dilute, 
dissolves  it  readily  with  evolution  of  binoxide  of  nitrogen.  Two  oxides  are 
known  which  form  salts ;  a  third,  or  peroxide,  is  said  to  exist. 

The  equivalent  of  copper  is  31-7 ;  its  symbol  Cu. 

Protoxide  of  copper  ;  black  oxide  ;  CuO.  —  This  is  the  base  of  the 
ordinary  blue  and  green  salts.  It  is  prepared  by  calcining  metallic  copper 
at  a  red-heat,  with  full  exposure  to  air,  or,  more  conveniently,  by  heating  to 
redness  the  nitrate,  which  sufi"ers  complete  decomposition.  When  a  salt  of 
this  oxide  is  mixed  with  caustic  alkali  in  excess,  a  bulky  pale  blue  precipi- 
tate of  hydrated  oxide  falls,  which,  when  the  whole  is  raised  to  the  boiling- 
point,  becomes  converted  into  a  heavy  dark  brown  powder;  this  also  is  an- 
hydrous oxide  of  copper,  the  hydrate  sufi"ering  decomposition,  even  in 
contact  with  water.  The  oxide  prepared  at  a  high  temperature  is  perfectly 
black  and  very  dense.  Protoxide  of  copper  is  soluble  in  acids,  and  forms  a 
series  of  very  important  salts,  being  isomorphous  with  magnesia. 

Suboxide  of  copper  ;  red  oxide  ;  CU2O. — The  suboxide  may  be  obtained 
by  heating  in  a  covered  crucible  a  mixture  of  5  parts  of  black  oxide  and  4 
parts  of  fine  cOpper-filings ;  or  by  adding  grape-sugar  to  a  solution  of  sul- 
phate of  copper,  and  then  putting  in  an  excess  of  caustic  potassa ;  the  blue 
solution,  heated  to  ebullition,  is  reduced  by  the  sugar  and  deposits  suboxide 
24 


278  COPPER. 

It  often  occurs  in  beautifully  transparent  ruby-red  crystals,  associated  -mth 
other  ores  of  copper,  and  can  be  obtained  in  this  state  by  artificial  means. 
This  substance  forras  colourless  salts  with  acids,  which  are  exceedingly 
instable,  and  tend  to  absorb  oxygen.  The  suboxide  communicates  to  glass  a 
magnificent  red  tint,  while  that  given  by  the  protoxide  is  green. 

Sulphate  of  coppee;  blue  vitriol;  CuO,S03-J-5HO.  —  This  beautiful 
Bait  is  prepared  by  dissolving  oxide  of  copper  in  sulphuric  acid,  or,  at  less 
expense,  by  oxidizing  the  sulphide.  It  forms  large  blue  crystals,  soluble  in 
4  parts  of  cold  and  2  of  boiling  water ;  by  heat  it  is  rendered  anhydrous  and 
nearly  white,  and  a  very  high  temperature  decomposed.  Sulphate  of  copper 
combines  with  the  sulphates  of  potassa  and  of  ammonia,  forming  pale  blue 
salts  which  contain  6  equivalents  of  water,  and  also  with  ammonia,  gene 
rating  a  remarkable  compound  of  deep  blue  colour,  capable  of  crystallizing. 

Nitrate  of  copper,  CuO,N05 -f  3H0.  —  The  nitrate  is  easily  made  by 
dissolving  the  metal  in  nitric  acid ;  it  forms  deep  blue  crystals,  very  soluble 
and  deliquescent.  It  is  highly  corrosive.  An  insoluble  subnitrate  is  known  ; 
it  is  green.     Nitrate  of  copper  also  combines  with  ammonia. 

Carbonates  op  copper.  — When  carbonate  of  soda  is  added  in  excess  to 
a  solution  of  sulphate  of  copper,  the  precipitate  is  at  first  pale  blue  and 
flocculent,  but  by  warming  it  becomes  sandy,  and  assumes  a  green  tint ;  in 
this  state  it  contains  CuOjCOg-j-CuOjHO-f-HO.  This  substance  is  prepared 
as  a  pigment.  The  beautiful  mineral  malachite  has  a  similar  composition, 
but  contains  one  equivalent  of  water  less.  Another  natural  compound,  not 
yet  artificially  imitated,  occurs  in  large  transparent  crystals  of  the  mosi 
intense  blue;  it  contains  2(CuO,C02)-|-CuO,HO.  Verditer,  made  by  decom- 
posing nitrate  of  copper  by  chalk,  is  said,  however,  to  have  a  somewhat 
similar  composition. 

Chloride  of  copper,  CuCl-f  2H0. — The  chloride  is  most  en sily  prepared 
by  dissolving  the  black  oxide  in  hydrochloric  acid,  and  concentrating  the 
green  solution  thence  resulting.  It  forms  green  crystals,  very  soluble  in 
water  and  in  alcohol ;  it  colours  the  flame  of  the  latter  green.  When  gently 
heated,  it  parts  with  its  water  of  crystallization  and  becomes  yellowish- 
brown  ;  at  a  high  temperature  it  loses  half  its  chlorine  and  becomes  con- 
verted into  the  subchloride.  The  latter  is  a  white  fusible  substance,  but 
little  soluble  in  water,  and  prone  to  oxidation ;  it  is  formed  when  copper- 
filings  or  copper-leaf  are  put  into  chlorine  gas. 

Aksknitb  of  copper;  Scheele's  green.  —  This  is  prepared  by  mixing 
solurtions  of  sulphate  of  copper  and  arsenite  of  potassa ;  it  falls  as_  a  bright 
green  insoluble  powder. 

The  characters  of  the  protosalts  of  copper  are  well  marked. 

Caustic  of  potassa  gives  a  pale  blue  precipitate  of  hydrate,  becoming 
blackish-brown  anhydrous  protoxide  on  boiling. 

Ammonia  also  throws  down  the  hydrate;  but,  when  in  excess,  re-dissolvea 
it,  yielding  an  intense  purplish  blue  solution. 

Carbonates  of  potassa  and  soda  give  pale  blue  precipitates,  insoluble  in 
excess. 

Carbonate  of  ammonia,  the  same,  but  soluble  with  deep  blue  colour. 

Ferrocyanide  of  potassium  gives  a  fine  red-brown  precipitate  of  ferrocya- 
nide  of  copper. 

Sulphuretted  hydrogen  and  sulphide  of  ammonium  afford  black  sulphide 
of  copper. 


The  alloys  of  copper  are  of  great  importance.     Brass  consists  of  copper 
alloyed  with  from  28  to  34  per  cent,  of  zinc ;  the  latter  may  be  added  ii- 


LEAD.  279 

rectly  to  the  melted  copper,  or  granulated  copper  may  be  heated  with  cala- 
mine and  charcoal-powder,  as  in  the  old  process.  Gun-metal,  a  most 
trustworthy  and  valuable  alloy,  consists  of  90  parts  copper  and  10  tin.  Bell 
and  speculum  metal  contain  a  still  larger  proportion  of  tin  ;  these  are  brittle, 
especially  the  last-named.  A  good  bronze  for  statues  is  made  of  91  parts 
copper,  2  parts  tin,  6  parts  zinc,  and  1  part  lead.  The  brass  of  the  ancients 
is  an  alloy  of  copper  with  tin. 


This  abundant  and  useful  metal  is  altogether  obtained  from  the  native  sul- 
phide, or  galena,  no  other  lead-ore  being  found  in  quantity.  The  reduction  is 
effected  in  a  reverberatory  furnace,  into  which  the  crushed  lead  ore  is  intro- 
duced and  roasted  for  some  time  at  a  dull  red-heat,  by  which  much  of  the 
sulphide  becomes  changed  by  oxidation  to  sulphate.  The  contents  of  the 
furnace  are  then  thoroughly  mixed,  and  the  temperature  raised,  when  the 
sulphate  and  sulphide  react  upon  each  other,  producing  sulphurous  acid  and 
metallic  lead.' 

Lead  is  a  soft  bluish  metal,  possessing  very  little  elasticity ;  its  specific 
gravity  is  11-4.5.  It  may  be  easily  rolled  out  into  plates,  or  drawn  into  coarse 
wire,  but  has  a  very  trifling  degree  of  strength.  Lead  melts  at  600°  (315° -SC) 
or  a  little  above,  and  at  a  white-heat  boils  and  volatilizes.  By  slow  cooling 
it  may  be  obtained  in  octahedral  crystals.  In  moist  air  this  metal  becomes 
coated  with  a  film  of  grey  matter,  thought  to  be  suboxide,  and  when  exposed 
to  the  atmosphere  in  a  melted  state  it  rapidly  absorbs  oxygen.  Dilute  acids, 
with  the  exception  of  nitric,  act  but  slowly  upon  lead.  Chemists  are  fami- 
liar with  four  oxides  of  lead,  only  one  of  which  possesses  basic  properties. 

The  equivalent  of  lead  is  103-7  ;  its  symbol  is  Pb. 

Protoxide;  litharge;  massicot;  PbO. — This  is  the  product  of  the 
direct  oxidation  of  the  metal.  It  is  most  conveniently  prepared  by  heating 
the  carbonate  to  dull  redness ;  common  litharge  is  impure  protoxide  which 
has  undergone  fusion.  Protoxide  of  lead  has  a  delicate  straw-yellow  colour, 
is  very  heavy,  and  slightly  soluble  in  water,  giving  an  alkaline  liquid.  At  a 
red-heat  it  melts,  and  tends  to  crystallize  on  cooling.  In  a  melted  state  it 
attacks  and  dissolves  siliceous  matter  with  astonishing  facility,  often  pene- 
trating an  earthen  crucible  in  a  few  minutes.  It  is  easily  reduced  when 
heated  with  organic  substances  of  any  kind  containing  carbon  or  hydrogen. 
Protoxide  of  lead  forms  a  large  class  of  salts,  which  are  colourless  if  the  acid 
itself  be  not  coloured. 

Red  oxide  ;  red-lead  ;  Pb304,  or  2PbO-t-Pb02.  —  The  composition  of 
this  substance  is  not  very  constant ;  it  is  prepared  by  exposing  for  a  long 
time  to  the  air,  at  a  very  faint  red-heat,  protoxide  of  lead  which  has  not  been 
fused ;  it  is  a  brilliant  red  and  extremely  heavy  powder,  decomposed  with 
evolution  of  oxygen  by  a  strong  heat,  and  converted  into  a  mixture  of  pro- 
toxide and  binoxide  by  acids.    It  is  used  as  a  cheap  substitute  for  vermilion. 

BiNOXiDE  OF  LEAD ;  PUCE  OR  BROWN  OXIDE ;  PbOg.  —  This  compound  is 
obtained  without  difficulty  by  digesting  red-lead  in  dilute  nitric  acid,  when 
nitrate  of  protoxide  is  dissolved  out  and  insoluble  binoxide  left  behind  in  the 
form  of  a  deep  brown  powder.  The  binoxide  is  decomposed  by  a  red-heat, 
yielding  up  one-half  of  its  oxygen.  Hydrochloric  acid  converts  it  into  chlo- 
ride of  lead  with  disengagement  of  chlorine ;  hot  oil  of  vitriol  forms  with  it 

r   Oxide  of    f  Lead Free. 

» Sulphate  of  I       lead       1  Oxygen -r===.^  2  Sulphurous  acid. 

lead         I  Sulphuric  j  Sulphur 
[_       acid        (3  Oxygen 

Sulphide  of  lead {\^^_^ ^^  , 


280  LEAD. 

sulphate  of  lead,  and  liberates  oxygen.  The  binoxide  is  very  useful  in  sepa- 
rating sulphurous  acid  from  certain  gaseous  mixtures,  sulphate  of  lead  being 
then  produced. 

Suboxide  of  lead,  PbgO. — When  oxalate  of  lead  is  heated  to  dull  redness 
in  a  retort,  a  grey  pulverulent  substance  is  left,  which  is  resolved  by  acids 
into  pi'otoxide  of  lead  and  metal.  It  absorbs  oxygen  with  great  rapidity 
when  heated,  and  even  when  simply  moistened  with  water  and  exposed  to 
the  air. 

Nitrate  of  lead,  PbO,N05,  — The  nitrate  may  be  obtained  by  dissolving 
carbonate  of  lead  in  nitric  acid,  or  by  acting  directly  upon  the  metal  by  the 
same  agent  with  the  aid  of  heat ;  it  is,  as  already  noticed,  a  by-product  in 
the  preparation  of  the  binoxide.  It  crystallizes  in  anhydrous  octahedrons, 
which  are  usually  milk-white  and  opaque ;  it  dissolves  in  7^  parts  of  cold 
water,  and  is  decomposed  by  heat,  yielding  nitrous  acid,  oxygen,  and  pro- 
toxide of  lead,  which  obstinately  retains  traces  of  nitrogen.  When  a  solution 
of  this  salt  is  boiled  with  an  additional  quantity  of  oxide  of  lead,  a  portion 
of  the  latter  is  dissolved,  and  a  basic  nitrate  generated,  which  may  be  had 
in  crystals.  Carbonic  acid  separates  this  excess  of  oxide  in  the  form  of  a 
white  compound  of  carbonate  and  hydrate  of  lead. 

Neutral  and  basic  compounds  of  oxide  of  lead  with  nitrous,  and  the  elements 
of  hyponitric  acid,  have  been  described.  These  last  are  probably  formed  by 
the  combination  of  a  nitrite  with  a  nitrate. 

Carbonate  of  lead;  white-lead;  PbOjCOg. — Carbonate  of  lead  is  some- 
times found  beautifully  crystallized  in  long  white  needles,  accompanying 
other  metallic  ores.  It  may  be  prepared  by  precipitating  in  the  cold  a  solu- 
tion of  the  nitrate  or  acetate  by  an  alkaline  carbonate ;  when  the  lead  solu- 
tion is  boiling,  the  precipitate  is  a  basic  salt,  containing  2(PbO,C02)-}-HO, 
PbO ;  it  is  also  manufactured  to  an  immense  extent  by  other  means  for  the  use 
of  the  painter.  Pure  carbonate  of  lead  is  a  soft,  white  powder,  of  great 
specific  gravity,  insoluble  in  water,  but  easily  dissolved  by  dilute  nitric  or 
acetic  acid. 

Of  the  many  methods  put  in  practice,  or  proposed,  for  making  white-lead, 
the  two  following  are  the  most  important  and  interesting :  —  One  of  these 
consists  in  forming  a  basic  nitrate  or  acetate  of  lead  by  boiling  finely  pow- 
dered litharge  with  the  neutral  salt.  This  solution  is  then  brought  into  con- 
tact with  carbonic  acid  gas ;  all  the  excess  of  oxide  previously  taken  up  by 
the  neutral  salt  is  at  once  precipitated  as  white-lead.  The  solution  strained 
or  pressed  from  the  latter  is  again  boiled  with  litharge,  and  treated  with  car- 
bonic acid,  these  processes  being  susceptible  of  indefinite  repetition,  when 
the  little  loss  of  neutral  salt  left  in  the  precipitates  is  compensated.  The 
second,  and  by  far  the  more  ancient  method,  is  rather  more  complex,  and  at 
first  sight  not  very  intelligible.  A  great  number  of  earthen  jars  are  pre- 
pared, into  each  of  which  is  poured  a  few  ounces  of  crude  vinegar ;  a  roll 
of  sheet-lead  is  then  introduced  in  such  a  manner  that  it  shall  neither  touch 
the  vinegar  nor  project  above  the  top  of  the  jar.  The  vessels  are  next  ar- 
ranged in  a  large  building,  side  by  side,  upon  a  layer  of  stable  manure,  or, 
still  better,  spent-tan,  and  closely  covered  with  boards.  A  second  layer  of 
tan  is  spread  upon  the  top  of  the  latter,  and  then  a  second  series  of  pots ; 
these  are  in  turn  covered  with  boards  and  decomposing  bark,  and  in  this 
manner  a  pile  of  many  alternations  is  constructed.  After  the  lapse  of  a  con- 
Biderable  time  the  .pile  is  taken  down  and  the  sheets  of  lead  removed  and 
carefully  unrolled ;  they  are  then  found  to  be  in  great  part  converted  into 
carbonate,  which  merely  requires  washing  and  grinding  to  be  fit  for  use. 
The  nature  of  this  curious  process  is  generally  explained  by  supposing  the 
vapour  of  vinegar  raised  by  the  high  temperature  of  the  fermenting  matter 
merely  to  act  as  a  carrier  between  tlie  carbonic  acid  evolved  from  the  tan 


LEAD  2?1 

and  the  oxide  of  lead  formed  under  the  influence  of  the  acid  vapour ;  a  neu- 
tral acetate,  a  basic  acetate,  and  a  carbonate  being  produced  in  succession, 
the  action  gradually  travelling  from  the  surface  inwards.  The  quantity  of 
acetic  acid  used  is,  in  relation  to  the  lead,  quite  trifling,  and  cannot  directly 
contribute  to  the  production  of  the  carbonate.  A  preference  is  still  given 
to  the  product  of  this  old  mode  of  manufacture  on  account  of  its  superiority 
of  opacity,  or  body,  over  that  obtained  by  precipitation.  Commercial  white- 
lead,  however  prepared,  always  contains  a  certain  proportion  of  hydrate. 

When  clean  metallic  lead  is  put  into  pure  water  and  exposed  to  the  atmo- 
sphare,  a  white,  crystalline,  scaly  powder  begins  to  show  itself  in  a  few 
hours,  and  very  rapidly  increases  in  quantity.  This  substance  may  consist 
of  hydrated  protoxide  of  lead,  formed  by  the  action  of  the  oxygen  dissolved 
in  the  water  and  from  the  lead.  It  is  slightly  soluble,  and  may  be  readily 
detected  in  the  water.  In  most  cases,  however,  the  formation  of  this  deposit 
is  due  to  the  action  of  the  carbonic  acid  dissolved  in  the  water ;  it  consists 
of  carbonate  in  combination  with  hydrate,  and  is  very  insoluble  in  water. 
When  common  river  or  spring  water  is  substituted  for  the  pure  liquid,  this 
effect  is  less  observable,  the  little  sulphate,  almost  invariably  present,  causing 
the  deposition  of  a  very  thin  but  closely  adherent  film  of  sulphate  of  lead 
upon  the  surface  of  the  metal,  which  protects  it  from  farther  action.  It  is 
on  this  account  that  leaden  cisterns  are  used  with  impunity,  at  least  in  most 
cases,  for  holding  water ;  if  the  latter  were  quite  pure,  it  .would  be  speedily 
contaminated  with  lead,  and  the  cistern  be  soon  destroyed.  Natural  water 
highly  charged  with  carbonic  acid  cannot,  under  any  circumstances,  be  kept 
in  lead,  or  passed  through  leaden  pipes  with  safety,  the  carbonate,  though 
very  insoluble  in  pure  water,  being  slightly  soluble  in  water  containing  car- 
bonic acid. 

Chloride  of  lead,  PbCl.  —  This  salt  is  prepared  by  mixing  strong  solu- 
tions of  acetate  of  lead  and  chloride  of  sodium ;  or  by  dissolving  litharge  in 
boiling  dilute  hydrochloric  acid,  and  setting  aside  the  filtered  solution  to 
cool.  Chloride  of  lead  crystallizes  in  brilliant,  colourless  needles,  which 
require  135  parts  of  cold  water  for  solution.  It  is  anhydrous ;  it  melts  when 
heated,  and  solidifies  on  cooling  to  a  horn-like  substance. 

Iodide  of  lead,  Pbl.  —  The  iodide  of  lead  separates  as  a  brilliant  yellow 
precipitate  when  a  soluble  salt  of  lead  is  mixed  with  iodide  of  potassium. 
This  compound  dissolves  in  boiling  water,  yielding  a  colourless  solution,  which 
deposits  the  iodide  on  cooling  in  splendid  golden-yellow  scales. 


The  soluble  salts  of  lead  thus  behave  with  reagents : — 

Caustic  potassa  and  soda  precipitate  a  white  hydrate,  freely  soluble  in 
excess. 

Ammonia  gives  a  similar  white  precipitate,  not  soluble  in  excess. 

The  carbonates  of  potassa,  soda,  and  ammonia,  precipitate  carbonate  of 
lead,  insoluble  in  excess. 

Sulphuric  acid  or  a  sulphate  causes  a  white  precipitate  of  sulphate  of  lead, 
insoluble  in  nitric  acid. 

Sulphuretted  hydrogen  and  sulphide  of  ammonium  throw  down  black 
sulphide  of  lead. 


An  alloy  of  2  parts  of  lead  and  1  of  tin  constitutes  p/?/TOier'«  solder;  thege 
proportions  reversed  give  a  more  fusible  compound  called  fine  so/der.  The 
lead  employed  in  the  manufacture  of  shot  is  combined  with  a  little  arsenic. 

»  Ammonia  gives  no  immediate  precipitate  with  the  acetate. 
24* 


282  TIN 


SECTION  V. 

OXIDABLE  METALS  PROPER,  WHOSE  OXIDES  FORM  WEAK 
BASES  OR  ACIDS. 


This  valuable  metal  occurs  in  the  state  of  oxide,  and  more  rarely  as  sul- 
phide ;  the  principal  tin  mines  are  those  of  the  Erzgebirge  in  Saxony  and 
Bohemia,  Malacca,  and  more  especially  Cornwall.  In  Cornwall  the  tin-stone 
is  found  as  a  constituent  of  metal  bearing  veins,  associated  with  copper  ore, 
in  granite  and  slate-rocks ;  and  as  an  alluvial  deposit,  mixed  with  rounded 
pebbles,  in  the  beds  of  several  small  rivers.  The  first  variety  is  called  mine- 
and  the  second  stream-tin.  Oxide  of  tin  is  also  found  disseminated  through 
the  rock  itself  in  small  crystals. 

To  prepare  the  ore  for  reduction,  it  is  stamped  to  powder,  washed,  to 
separate  as  much  as  possible  of  the  earthy  matter,  and  roasted  to  expel 
sulphur  and  arsenic ;  it  is  then  strongly  heated  with  coal,  and  the  metal  thus 
obtained  cast  into  large  blocks,  which,  after  being  assayed,  receive  the  stamp 
of  the  Duchy.  Two  varieties  of  commercial  tin  are  known,  called  grain-  and 
bar-tin  ;  the  first  is  the  best ;  it  is  prepared  from  the  stream  ore. 

Pure  tin  has  a  white  colour,  approaching  to  that  of  silver ;  it  is  soft  and 
malleable,  and  when  bent  or  twisted  emits  a  peculiar  crackling  sound  ;  it  has 
a  density  of  7-3  and  melts  at  442°  (227o-77C).  Tin  is  but  little  acted  upon 
by  air  and  water,  even  conjointly;  when,  heated  above  its  melting-point  it 
oxidizes  rapidly,  becoming  converted  into  a  whitish  powder,  used  in  the  arts 
for  polishing,  under  the  name  of  putty-poivder.  The  metal  is  easily  attacked 
and  dissolved  by  hydrochloric  acid,  with  evolution  of  hydrogen;  nitric  acid 
acts  with  great  energy,  converting  it  into  a  white  hydrate  of  the  binoxide. 
There  are  two  well-marked  oxides  of  tin,  which  act  as  feeble  bases  or  acids, 
according  to  circumstances,  and  a  third,  which  has  been  less  studied. 

The  equivalent  of  tin  is  58 ;  its  symbol  is  Sn. 

Protoxide  of  tin,  SnO. — When  solution  of  protochloride  of  tin  is  mixed 
with  carbonate  of  potassa,  a  white  hydrate  of  the  protoxide  falls,  the  car- 
bonic acid  being  at  the  same  time  extricated.  When  this  is  carefully  washed, 
dried,  and  heated  in  an  atmosphere  of  carbonic  acid,  it  loses  water,  and 
changes  to  a  dense  black  powder,  which  is  permanent  in  the  air,  but  takes 
fire  on  the  approach  of  a  red-hot  body,  and  burns  like  tinder,  producing 
binoxide.  The  hydrate  is  freely  soluble  in  caustic  potassa ;  the  solution 
decomposes  by  keeping  into  metallic  tin  and  binoxide. 

Sesquioxide  of  tin,  SngOg.  —  The  sesquioxide  is  produced  by  the  action 
of  hydrated  sesquioxide  of  iron  upon  protochloride  of  tin ;  it  is  a  greyish, 
Bliray  substance,  soluble  in  hydrochloric  acid,  and  in  ammonia.  This  oxide 
has  been  but  little  examined. 

Binoxide  of  tin,  SnOj. — This  substance  is  obtained  in  two  different  states, 
having  properties  altogether  dissimilar.  When  bichloride  of  tin  is  precipi- 
tated by  an  alkali,  a  white  bulky  hydrate  appears,  which  is  freely  soluble  in 


TIN 


m 


acids.  If,  on  the  other  hand,  the  bichloride  be  boiled  with  excess  of  nitric 
acid,  or  if  that  acid  be  made  to  act  directly  on  metallic  tin,  a  white  sub- 
stance is  produced,  which  refuses  altogether  to  dissolve  in  acids,  and  pos- 
sesses properties  diflfering  in  other  respects  from  those  of  the  first  modifica- 
tion. Both  these  ■varieties  of  binoxide  of  tin  have  the  sanje  composition, 
and  when  ignited,  leave  the  pure  binoxide  of  a  pale  lemon-yellow  tint. 
Both  dissolve  in  caustic  alkali,  and  are  precipitated  with  unchanged  proper- 
ties by  an  acid.     The  two  hydrates  redden  litmus-paper.* 

PiiOTOOHLORiDE  OF  TIN,  SuCl.  —  The  protochloHde  is  easily  made  by  dis- 
solving metallic  tin  in  hot  hydrochloric  acid.  It  crystallizes  in  needles  con- 
taining 2  equivalents  of  water,  which  are  freely  soluble  in  a  small  quantity 
of  water,  but  arfe  apt  to  be  decomposed  in  part  when  put  into  a  large  mass, 
unless  hydrochloric  acid  in  excess  be  present.  The  anhydrous  chloride  may 
be  obtained  by  distilling  a  mixture  of  calomel  and  powdered  tin,  prepared 
by  agitating  the  melted  metal  in  a  wooden  box  until  it  solidifies.  The  chlo- 
ride is  a  grey,  resinous-looking  substance,  fusible  below  redness,  and  volatile 
at  a  high  temperature.  Solution  of  protochloride  of  tin  is  employed  as  a 
deoxidizing  agent ;  it  reduces  the  salts  of  mercury  and  other  metals  of  the 
same  class. 

BiCHLomDE  or  perchloeide  of  tin,  SnClg. — This  is  an  old  and  very  cu- 
rious compound,  formerly  called  fuming  liquor  of  Libavius.  It  is  made  by 
exposing  metallic  tin  to  the  action  of  chlorine,  or,  more  conveniently,  by 
distilling  a  mixture  of  1  part  of  powdered  tin,  and  5  parts  of  corrosive  sub- 
limate. The  bichloride  is  a  thin,  colourless,  mobile  liquid ;  it  boils  at  248*' 
(120°C),  and  yields  a  colourless  invisible  vapour.  It  fumes  in  the  air,  and 
when  mixed  with  a  third  part  of  water,  solidifies  to  a  crystalline  mass.  Tlie 
solution  of  bichloride  is  much  employed  by  the  dyer  as  a  mordant ;  it  is  com- 
monly prepared  by  dissolving  metallic  tin  in  a  mixture  of  hydrochloric  and 
nitric  acids,  care  being  taken  to  avoid  too  great  elevation  of  temperature. 

Sulphides  of  tin. — Protosulphide,  SnS,  is  prepared  by  fusing  tin  with  ex- 
cess of  sulphur,  and  strongly  heating  the  product.  It  is  a  lead-grey,  brittle 
substance,  fusible  by  a  red-heat,  and  soluble  with  evolution  of  sulphuretted 
hydrogen  in  hot  hydrochloric  acid.  A  sesquisulphide  may  be  formed  by  gently 
heating  the  above  compound  with  a  third  of  its  weight  of  sulphur ;  it  is  yel- 
lowish-grey, and  easily  decomposed  by  heat.  Bisulphide,  SnSg,  or  Mosaic 
gold,  is  prepared  by  exposing  to  a  low  red-heat,  in  a  glass  flask,  a  mixture 
of  12  parts  of  tin,  6  of  mercury,  6  of  sal-ammoniac,  and  7  of  flowers  of 
sulphur.  Sal-ammoniac,  cinnabar,  and  protochloride  of  tin  sublime,  while 
the  bisulphide  remains  at  the  bottom  of  the  vessel  in  the  form  of  brilliant 
gold-coloured  scales ;  it  is  used  as  a  substitute  for  gold-powder. 

Salts  of  tin  are  thus  distinguished ; — 

Protoxide. 
Caustic  alkalis ;  white  hydrate,  soluble  in  excess. 
Ammonia;  carbonates  of  potassa,  ^  ,,.,..     ,     ,     .  ^     •      t  x.-, 

soda,  and  ammonia l^^'*®  hydrate,  nearly  jisoluble  in 

[      excess. 

Sulphuretted  hydrogen )  t>i     ^  •  -j.  x      /.        ^       i  t.j 

Sulphide  of  ammonTum  }  ^^^^^  precipitate  of  protosulphide. 

Binoxide. 
Caustic  alkalis ;  white  hydrate,  soluble  in  excess. 
Ammonia ;  white  hydrate,  slightly  soluble  in  excess. 

«  Fremy  has  called  the  first  of  these  oxides  stannic  acid  SnOa.  The  second  he  hait  na'ned 
metastannic  acid  SnsOio.  See  also  H.  Rose  Pogg.  Ann.  Ixxv.  1,  who  thinks  that  there  ar* 
other  modifications  of  this  oxide  of  tin. 


284  TUNGSTEN  —  MOLYBDENUM. 

Alkaline  carbonates ;  white  hydrates,  slightly  soluble  in  excess 
Carbonate  of  ammonia ;   white  hydrate,  insoluble. 
Sulphuretted  hydrogen  ;  yellow  precipitate  of  sulphide. 
Sulphide  of  ammonium  ;  the  same,  soluble  in  excess. 

Terchloride  of  gold,  added  to  a  dilute  solution  of  protochloride  of  tin, 
gives  rise  to  a  brownish-purple  precipitate,  called  purple  of  Cassius,  very 
characteristic,  whose  nature  is  not  thoroughly  understood ;  it  is  supposed  to 
be  a  combination  of  oxide  of  gold  and  sesquioxide  of  tin,  in  which  the  latter 
acts  as  an  acid.  Heat  resolves  it  into  a  mixture  of  metallic  gold  and  binox- 
ide  of  tin.     Purple  of  Cassius  is  employed  in  enamel-painting. 


The  useful  applications  of  tin  are  very  numerous.  Tinned-plate  consists 
of  iron  superficially  alloyed  with  this  metal ;  pewter,  of  the  best  kind,  is 
chiefly  tin,  hardened  by  the  admixture  of  a  little  antimony,  &c.  Cooking 
vessels  of  copper  are  usually  tinned  in  the  interior. 

TUNGSTEN    (WOLFBAMIUM). 

Tungsten  is  found,  as  tungstate  of  protoxide  of  iron,  in  the  mineral  wolf- 
ram, tolerable  abundant  in  Cornwall ;  a  native  tungstate  of  lime  is  also  oc- 
casionally met  with.  Metallic  tungsten  is  obtained  in  the  state  of  a  dark 
grey  powder,  by  strongly  heating  tungstic  acid  in  a  stream  of  hydrogen,  but 
requires  for  fusion  an  exceedingly  high  temperature.  It  is  a  white  metal, 
very  hard  and  brittle;  it  has  a  density  of  17-4.  Heated  to  redness  in  the 
air,  it  takes  fire,  and  reproduces  tungstic  acid. 

The  equivalent  of  tungsten  is  92,  its  symbol  is  W  (wolframium). 

BiNOXiDE  OF  TUNGSTEN,  WOj-  —  This  is  most  easily  prepared  by  exposing 
tungstic  acid  to  hydrogen,  at  a  temperature  which  does  not  exceed  dull  red- 
ness. It  is  a  brown  powder,  sometimes  assuming  a  crystalline  appearance 
and  an  imperfect  metallic  lustre.  It  takes  fire  when  heated  in  the  air,  and 
burns,  like  the  metal  itself,  to  tungstic  acid.  The  binoxide  forms  no  salts 
with  acids. 

Tungstic  acid,  WOj. — When  tungstate  of  lime  can  be  obtained,  simple 
digestion  in  hot  nitric  acid  is  sufficient  to  remove  the  base,  and  liberate  the 
tungstic  acid  in  a  state  of  tolerable  purity:  its  extraction  from  wolfram, 
which  contains  tungstic  acid  or  oxide  of  tungsten  in  association  with  the 
oxides  of  iron  and  manganese,  is  more  difficult.  Tungstic  acid  is  a  yellow 
powder,  insoluble  in  water,  and  freely  dissolved  by  caustic  alkalis.  When 
strongly  ignited  in  the  open  air,  it  assumes  a  greenish  tint. 

Intehmediate  or  blue  oxide  of  tungsten,  W205,=W02,W03. — This  sub- 
Btance  is  obtained  by  heating  tungstate  of  ammonia,  or  by  exposing  the 
brown  binoxide  to  the  action  of  hydrogen  at  a  very  low  temperature.  The 
same  compound  appears  to  be  produced  if  tungstic  acid  be  separated  froni 
one  of  its  salts,  by  hydrochloric  acid  and  the  liquid  be  digested  with  metallic 
zinc,  when  the  solution  or  the  precipitate  assumes  a  beautiful  blue  colour, 
which  is  very  characteristic  of  this  metal. 

Two  chlorides  and  two  sulphides  of  tungsten  are  known  to  exist. 

molybdenum. 

Metallic  molybdenum  is  obtained  by  exposing  molybdic  acid  in  a  charcoal- 
lined  crucible  to  the  most  intense  heat  that  can  be  obtained.  It  is  a  white, 
brittle,  and  exceedingly  infusible  metal,  having  a  density  of  8-6,  and  oxi- 
lizing,  when  heated  in  the  air,  to  molybdic  acid. 

The  equivalent  of  molybdenum  is  46 ;  its  symbol  is  Mo. 

Peotoxide  of  molybdenum,  MoO.  —  Molybdate  of  potassa  is  mixed  with 


VANADIUM.  285 

excMS  of  hydrochloric  acid,  by  which  the  molybdic  acid  first  precipitated  is 
re-dissolved ;  into  this  acid  solution  zinc  is  put :  a  mixture  of  chloride  of 
zinc  and  protochloride  of  molybdenum  results.  A  large  quantity  of  caustic 
potassa  is  then  added,  which  precipitates  a  black  hydrate  of  the  protoxide 
of  molybdenum,  and  retains  in  solution  the  oxide  of  zinc.  The  freshly  pre- 
cipitated protoxide  is  soluble  in  acids  and  in  carbonate  of  ammonia ;  when 
heated  in  the  air,  it  burns  to  binoxide. 

BiNOxiDE  OF  MOLYBDENUM,  MoOg. — This  is  obtained  in  the  anhydrous  con- 
dition by  heating  molybdate  of  soda  with  sal-ammoniac,  the  molybdic  acid 
being  reduced  to  binoxide  by  the  hydrogen  of  the  ammoniacal  salt ;  or,  in  a 
hydrated  condition,  by  digesting  metallic  copper  in  a  solution  of  molybdic 
acid  in  hydrochloric  acid,  until  the  liquid  assumes  a  red  colour,  and  then 
adding  a  large  excess  of  ammonia.  The  anhydrous  binoxide  is  deep  brown, 
and  insoluble  in  acids ;  the  hydrate  resembles  hydrate  of  sesquioxide  of  iron, 
and  dissolves  in  acids,  yielding  red  solutions.  «lt  is  converted  into  molybdic 
acid  by  strong  nitric  acid. 

Molybdic  acid,  M0O3. — The  native  bisulphide  of  molybdenum  is  roasted, 
at  a  red-heat,  in  an  open  vessel,  and  the  impure  molybdic  acid  thence  re- 
sulting dissolved  in  ammonia.  The  filtered  solution  is  evaporated  to  dryness, 
the  salt  taken  up  by  water,  and  purified  by  crystallization.  It  is,  lastly, 
decomposed  by  heat,  and  the  ammonia  expelled.  Molybdic  acid  is  a  white 
crystalline  powder,  fusible  at  a  red-heat,  and  slightly  soluble  in  water.  It 
is  dissolved  with  ease  by  the  alkalis.  It  forms  two  series  of  salts,  namely, 
neutral  molybdates  MO,Mo03,  and  acid  molybdatea  MO,2Mo03.  Three 
chloi'ides,  and  as  many  sulphides  of  molybdenum,  are  described. 

VANADIUM. 

Vanadium  is  found,  in  small  quantity,  in  one  of  the  Swedish  iron  ores, 
and  also  as  vanadate  of  lead.  It  has  also  been  discovered  in  the  iron  slag  of 
Stafi"ordshire.  The  most  successful  process  for  obtaining  the  metal  is  said 
to  be  the  following:  —  The  liquid  chloride  of  vanadium  is  introduced  into  a 
bulb,  blown  in  a  glass  tube,  and  dry  ammcniucal  gas  passed  over  it;  the 
latter  is  absorbed,  and  a  white  saline  mass  produced.  When  this  is  heated 
by  the  flame  of  a  spirit-lamp,  chloride  of  ammonium  is  volatilized,  and 
metallic  vanadium  left  behind.  It  is  a  white  brittle  substance,  of  perfect 
metallic  lustre,  and  a  very  high  degree  of  infusibility ;  it  is  neither  oxidized 
by  air  or  water,  nor  attacked  by  sulphuric,  hydrochloric,  or  even  hydrofluoric 
acid  ;  aqua  regia  dissolves  it,  yielding  a  deep  blue  solution. 

The  equivalent  of  vanadium  is  68-6 ;  its  symbol  is  V. 

Protoxide  of  vanadium,  VO.  —  This  is  prepared  by  heating  vanadic  acid 
in  contact  with  charcoal  or  hydrogen ;  it  has  a  black  colour,  and  imperfect 
metallic  lustre,  conducts  electricity,  and  is  very  infusible.  Heated  in  the 
air,  it  burns  to  binoxide.  Nitric  acid  produces  the  same  efi"ect,  a  blue  nitrate 
of  the  binoxide  being  generated.     It  does  not  form  salts. 

Binoxide  of  vanadium,  VOj.  —  The  binoxide  is  obtained  by  heating  a 
mixture  of  10  parts  protoxide  of  vanadium,  and  12  of  vanadic  acid  in  a  vessel 
filled  with  carbonic  acid  gas;  or  by  adding  a  slight  excess  of  carbonate  of 
soda  to  a  salt  of  the  binoxide;  in  the  latter  case  it  falls  as  a  greyish-whito 
hydrate,  readily  becoming  brown  by  absorption  of  oxygen.  The  anhydrous 
oxide  is  a  black  insoluble  powder,  convertible  by  heat  and  air  into  vanadic 
acid.  It  forms  a  series  of  blue  salts,  which  have  a  tendency  to  become  green 
and  ultimately  red,  by  the  production  of  vanadic  acid.  Binoxide  of  vanadium 
also  unites  with  alkalis. 

Vanadic  acid,  VO3.  —  The  native  vandate  of  lead  is  dissolved  in  nitric 
acid,  and  the  lead  and  arsenic  precipitated  by  sulphuretted  hydrogen,  which 
at  the  same  time  reduces  the  vanadic  acid  to  binoxide  of  vanadium.    The 


%M        TANTALUM  —  NIOBIUM     AND    PELOPIUM. 

bhie  filtered  solution  is  then  evaporated  to  dryness,  and  the  residue  digested 
in  amnronia,  which  dissolves  out  the  vanadic  acid  reproduced  during  evapo- 
ration. Into  this  solution  a  lump  of  sal-ammoniac  is  put;  as  that  salt  dis- 
solves, vanadate  of  ammonia  subsides  as  a  white  powder,  being  scarcely  solu- 
ble in  a  saturated  solution  of  chloride  of  ammonium.  By  exposure  to  a  tem- 
perature below  redness  in  an  open  crucible,  the  ammonia  is  expelled,  and 
vanadic  acid  left.  It  has  a  dark-red  colour,  and  melts  even  below  a  red- 
heat  ;  water  dissolves  it  sparingly,  and  acids  with  greater  ease ;  the  solutions 
easily  suffer  deoxidation.  It  unites  with  bases,  forming  a  series  of  red  or 
yellow  salts,  of  which  those  of  the  alkalis  are  soluble  in  water. 

Chlokides  of  vanadium. — The  bichloride  is  prepared  by  digesting  vanadic 
acid  in  hydrochloric  acid,  passing  a  stream  of  sulphuretted  hydrogen,  and 
evaporating  the  whole  to  dryness.  A  brown  residue  is  left,  which  yields  a 
blue  solution  with  water  and  an  insoluble  oxi chloride.  The  icrchloride  is  a 
yellow  liquid  obtained  by  jJlissing  chlorine  over  a  mixture  of  protoxide  of 
vanadium  and  charcoal.  It  is  converted  by  water  into  hydrochloric  and 
vanadic  acids. 

Two  sulphides,  corresponding  to  the  chlorides,  exist. 

TANTALUM  (COLUMBIUm). 

This  is  an  exceedingly  rare  substance;  it  is  found  in  the  minerals  iantalite 
atid  ytlro-fantalite,  and  may  be  obtained  pure  by  heating  with  potassium  the 
double  fluoride  of  tantalum  and  potassium.  It  is  a  grey  metal,  but  little 
acted  on  by  the  ordinary  acids,  and  burning  to  tantalic  acid  when  heated  in 
the  air,  or  when  fused  with  hydrate  of  potassa. 

The  equivalent  of  tantalum  is  184  ;  its  symbol  is  T. 

BiNOXiDK  OF  TANTALUM,  TOg.  —  When  tantalic  acid  is  heated  to  whiteness 
in  a  crucible  lined  with  charcoal,  the  greater  part  is  converted  into  this  sub- 
stance. It  is  a  dark-brown  powder,  insoluble  in  acids,  and  easily  changed 
by  oxidation  to  tantalic  acid. 

Tantalic  acid,  TO3.  —  The  powdered  ore  is  fused  with  three  or  four  times 
its  weight  of  carbonate  of  potassa,  and  the  product  digested  with  water; 
from  this  solution  acids  precipitate  a  white  hydrate  of  the  body  in  question. 
It  is  soluble  in  acids,  but  forms  with  them  no  definite  compounds ;  with  al- 
kalis it  yields,  on  the  contrary,  crystallizable  salts.  The  specific  gravity  of 
the  acid  varies  7-03  to  8-26. 

NIOBIUM  AND  PELOPIUM. 

The  oxides  of  these  two  metals  exist  in  the  tantalite  of  Bodenmais  in  Ba- 
varia. "When  the  supposed  tantalic  acid  from  this  source  is  mixed  with  dry 
powdered  charcoal,  and  heated  to  redness  in  a  current  of  chlorine  gas,  a 
sublimate  is  obtained  of  a  yellow,  readily  fusible,  and  very  volatile  substance, 
the 'chloride  of  pelopium,  and  a  white,  infusible,  less  volatile  body,  the  chlo- 
ride of  niobium.  The  true  chloride  of  tantalum,  from  the  Finland  tantalite, 
much  resembles  chloride  of  pelopium.  The  American  tantalite  contains  nio- 
bic,  pelopic,  and  tungstic  acids,  the  former  in  greatest  quantity. 

All  these  chlorides  are  decomposed  by  water,  with  production  of  hydro- 
chloric acid  and  the  insoluble  acids  of  the  metals  in  the  hydrated  state.  In 
properties  these  bodies  greatly  resemble  each  other.  When  heated  to  redness, 
they  exhibit  strongly  the  phenomenon  of  incandescence.  While  hot,  tantalic 
acid  remains  white,  pelopic  acid  is  rendered  slightly  yellowish  and  has  a  spe- 
cific giavity  varying  from  5-79  to. 6-37,  and  niobic  acid  becomes  dark  yellow, 
with  a  specific  gravity  between  4-56  and  6-26. 

Tantalum,  niobium,  and  pelopium  may  be  obtained  in  a  finely-divided  me- 
tallic state  by  the  action  of  ammonia  on  their  respective  chlorides  at  a  high 


TITANIUM  —  ANTIMONY.  287 

temperature.     So  prepared,  they  are  black,  pulverulent,  not  acted  on  bj 
water,  but  burning,  when  heated  in  the  air,  to  acids. 

TITANIUM. 

Crystallized  oxide  of  titanium  is  found  in  nature  in  the  forms  of  titaniU 
and  anaiate.  Occasionally  in  the  slag  adherent  to  the  bottom  of  blast-fumacea 
in  which  iron  ore  is  reduced  small  brilliant  copper-coloured  cubes,  hard 
enough  to  scratch  glass,  and  in  the  highest  degree  infusible  are  found.  Thia 
substance,  of  which  a  single  smelting  furnace  in  the  Hartz  produced  as  much 
as  80  pounds,  was  formerly  believed  to  be  metallic  titanium.  Recent  re- 
searches of  Wohler,  however,  have  shown  it  to  be  a  combination  of  cyanide 
of  titanium  with  nitride  of  titanium.  When  these  crystals  are  powdered, 
mixed  with  hydrate  of  potassa  and  fused,  ammonia  is  evolved,  and  titanate 
of  potassa  is  formed.  Metallic  titanium  in  a  finely  divided  state  may  be  ob- 
tained by  heating  fluoride  of  titanium  and  potassium  with  potassium.  There 
are  two  compounds  of  this  substance  with  oxygen;  viz.  an  oxide  and  an 
acid :  very  little  is  known  respecting  the  former. 

The  equivalent  of  titanium  is  25  ;  its  symbol  is  Ti. 

Titanic  acid,  Ti02. — Titanate,  or  titaniferous  iron  ore,  is  reduced  to  fine 
powder  and  fused  with  twice  its  weight  of  carbonate  of  potassa,  powdered, 
dissolved  in  dilute  hydrofluoric  acid  when  titanofluoride  of  titanium  and 
potassium  soon  begins  to  separate.  From  its  hot  aqueous  solution  snow-like 
titanate  of  ammonia  is  precipitated  by  ammonia,  which  is  easily  soluble  in 
hydrochloric  acid,  and  when  ignited  gives  pure  titanic  acid.  When  pure  the 
acid  is  quite  white ;  it  is,  when  recently  precipitated  from  solutions,  soluble 
in  acids,  but  the  solutions  are  decomposed  by  mere  boiling.  After  ignition 
it  is  no  longer  soluble,  passing  over  into  metatitanic  acid.  Titanic  acid,  on 
the  whole,  very  much  resembles  silica,  and  is  probably  often  overlooked  and 
confounded  with  that  substance  in  analytical  researches. 

Bichloride  of  titanium. — This  is  a  colourless,  volatile  liquid,  resembling 
bichloride  of  tin ;  it  is  obtained  by  passing  chlorine  over  a  mixture  of  titanic 
acid  and  charcoal  at  a  high  temperature.  It  unites  very  violently  with 
water.  On  passing  the  vapour  with  hydrogen  through  a  red-hot  tube, 
hydrochloric  acid  and  a  new  compound  TijClj  are  formed. 

antimony. 

This  important  metal  is  found  chiefly  in  the  state  of  sulphide.  The  ore  is 
freed  by  fusion  from  earthy  impurities,  and  is  afterwards  decomposed  by 
heating  with  metallic  iron  or  carbonate  of  potassa,  which  retains  the  sulphur. 
Antimony  has  a  bluish-white  colour  and  strong  lustre ;  it  is  extremely 
brittle,  being  reduced  to  powder  with  the  utmost  ease.  Its  specific  gravity 
is  6-8 ;  it  melts  at  a  temperature  just  short  of  redness,  and  boils  and  vola- 
tilizes at  a  white-heat.  This  metal  has  always  a  distinct  crystalline,  platy 
structure,  but  by  particular  management  it  may  be  obtained  in  crystals, 
which  are  rhombohedral.  Antimony  is  not  oxidized  by  the  air  at  common 
temperatures ;  strongly  heated,  it  burns  with  a  white  flame,  producing  ter- 
oxide,  which  is  often  deposited  in  beautiful  crystals.  It  is  dissolved  by  hot 
hydrochloric  acid  with  evolution  of  hydrogen  and  production  of  terchloride. 
Nitric  acid  oxidizes  it  to  antimonic  acid,  which  is  insoluble  in  that  men- 
struum. There  are  three  compounds  of  antimony  and  oxygen ;  the  first  has 
doubtful  basic  properties,  the  second  is  indifferent,  and  the  third  is  an  acid 

The  equivalent  of  antimony  is  129.     Its  symbol  is  Sb  (stibium). 

Teroxide  of  antimony,  SbOg.  —  This  compound  may  be  prepa>ed  by 
several  methods :  as  by  burning  metallic  antimony  at  the  bottom  of  a  large 
red-hot  crucible,  in  which  case  it  is  obtained  in  brilliant  crystals ;  or  by 
pouring  ^o'aiion  of  terchloride  of  aniimony  into  water,  and  digesting  thi 


288  ANTIMONY. 

resulting  precipitate  with  a  solution  of  carbonate  of  soda.  The  teroxide 
thus  produced  is  anhydrous ;  it  is  a  pale  buff-coloured  powder,  fusible  at  a 
red-heat,  and  volatile  in  a  close  vessel,  but  in  contact  with  air,  it,  at  a  high 
temperature,  absorbs  oxygen  and  becomes  changed  to  the  intermediate  oxide. 
There  exists  a  sulphate,  nitrate,  and  oxalate  of  teroxide  of  antimony.  When 
boiled  with  cream  of  tartar  (bitartrate  of  potassa),  it  is  dissolved,  and  the 
solution  yields,  on  evaporation,  crystals  of  tartar-emetic,  which  is  almost  the 
only  compound  of  teroxide  of  antimony  with  an  acid  which  bears  admixture 
with  water  without  decomposition.  An  impure  oxide  for  this  purpose  is 
sometimes  prepared  by  carefully  roasting  the  powdered  sulphide  in  a  rever- 
beratory  furnace,  and  raising  the  heat  at  the  end  of  the  process,  so  as  to  fuse 
the  product;  it  has  long  been  known  under  the  name  of  glass  of  antimony. 

Intermediate  oxide,  Sb04  =  Sb03,Sb05.  —  This  is  the  ultimate  product 
of  the  oxidation  of  the  metal  by  heat  and  air ;  it  is  a  greyish  white  powder, 
infusible,  and  destitute  of  volatility ;  it  is  insoluble  in  water  and  in  acids, 
except  when  recently  precipitated.  "When  treated  with  tartaric  acid  or 
bitartrate  of  potassa,  teroxide  of  antimony  is  dissolve<l,  antimonic  acid 
remaining  behind ;  alkalis,  on  the  other  hand,  remove  antimonic  acid,  ter- 
cxide  of  antimony  being  left. 

Antimonic  acid,  SbOg.  —  When  strong  nitric  acid  is  made  to  act  upon 
metallic  antimony,  the  metal  is  oxidized  to  its  highest  point,  and  antimonic 
acid  produced,  which  is  insoluble.  By  exposure  to  a  heat  short  of  redness, 
it  is  rendered  anhydrous,  and  then  presents  the  appearance  of  a  pale  straw- 
coloured  powder,  insoluble  in  water  and  acids.  It  is  decomposed  by  a  red- 
heat,  yielding  the  intermediate  oxide,  with  the  loss  of  oxygen. 

Antimonic  acid  is  likewise  obtained  by  decomposing  pentachloride  of  anti- 
mony and  an  excess  of  water,  when,  together  with  the  metallic  acid,  hydro- 
acid  is  produced.  The  hydrated  antimonic  acid  produced  by  the  two  pro- 
cesses mentioned,  differs  in  many  of  its  properties,  and  especially  in  its 
deportment  with  laases.  The  substance  produced  by  nitric  acid  is  monobasic, 
producing  salts  of  the  formula  MOjSbOg,  the  other  is  bibasic,  and  forms  two 
series  of  salts  of  the  composition  2MO,Sb05  and  M0,H0,Sb05.  In  order  to 
distinguish  the  two  modifications,  M.  Fremy,  who  first  pointed  out  the  bibasic 
nature  of  the  acid  obtained  from  the  pentachloride,  has  proposed  to  distin- 
guish it  as  metantimonic  acid.  Among  the  salts  of  the  latter,  an  acid 
metantimonate  of  potassa  KO,HO,Sb05-j-6HO,  is  to  be  noticed,  which  yields 
a  precipitate  with  soda-salts.  It  is  the  only  reagent  which  precipitates  soda, 
but  must  be  employed  with  great  care  and  circumspection.  It  is  obtained 
by  fusing  antimonic  acid  with  an  excess  of  potassa  in  a  silver  crucible,  dis- 
solving the  fused  mass  in  a  small  quantity  of  cold  water,  and  allowing  it  to 
crystallize  in  vacuo.  The  crystals  which  form  are  metantimonate  of  potassa 
2K0,  SbOg,  which,  when  dissolved  in  pure  water,  are  decomposed  into  free 
potassa  and  acid  metantimonate. 

Terchlobide  of  antimony  ;  butter  of  antimony  ;  SbClg. — This  substance 
is  produced  when  sulphuretted  hydrogen  is  prepared  by  the  action  of  strong 
hydrochloric  acid  on  tersulphide  of  antimony.  The  impure  and  highly  acid' 
solution  thus  obtained  is  put  into  a  retort  and  distilled  until  each  drop  of 
the  condensed  product,  on  falling  into -the  aqueous  liquid  of  the  receiver, 
produces  a  copious  white  precipitate.  The  receiver  is  then  changed,  and  the 
distillation  continued.  Pure  terchloride  of  antimony  passes  over,  and  soli- 
difies on  cooling  to  a  white  and  highly  crystalline  mass,  ft-om  which  the  air 
requires  to  be  carefully  excluded.  The  same  compound  is  formed  by  distil- 
ling metallic  antimony  in  powder  with  2^  times  its  weight  of  corrosive  subli- 
mate. Terchloride  of  antimony  is  very  deliquescent ;  it  dissolves  in  strong 
hydrochloric  acid  without  decomposition,  and  the  solution  poured  into  water 
gives  rise  to  a  white  bulky  precipitate,  which,  after  a  short  time,  becomes 


ANTIMONY.  289 

highly  crystalline,  and  assumes  a  pale  fawn  colour.  This  is  the  old  powder 
of  Algaroth  ;  it  is  a  compound  of  terchloride  and  teroxide  of  antimony.  Al- 
kaline solutions  extract  the  chloride  and  leave  teroxide  of  antimony.  Finely 
powdered  antimony  thrown  into  chlorine  gas  inflames. 

Pkntachoridb  of  Antimony,  corresponding  to  antimonic  acid,  is  formed 
by  passing  a  stream  of  chlorine  gas  ever  gently  heated  metallic  antimony ;  a 
mixture  of  the  two  chlorides  results,  which  may  be  separated  by  distillation. 
The  pentachloride  is  a  colourless  volatile  liquid,  which  forms  a  crystalline 
compound  with  a  small  portion  of  water,  but  is  decomposed  by  a  larger  quan- 
tity into  antimonic  and  hydrochloric  acids. 

Tersulphide  of  antimony  ;  crude  antimony  ;  SbSg. — The  native  sulphide 
is  a  lead-grey,  brittle  substance,  having  a  radiated  crystalline  texture,  and 
is  easily  fusible.  It  may  be  prepared  artificially  by  melting  together  anti- 
mony and  sulphur.  When  a  solution  of  tartar-emetic  is  precipitated  by  sul- 
phuretted hydrogen,  a  brick-red  precipitate  falls,  which  is  the  same  substance 
combined  with  a  little  water.  If  the  precipitate  be  dried  and  gently  heated, 
the  water  may  be  expelled  without  other  change  of  colour  than  a  little  dark- 
ening, but  at  a  higher  temperature  it  assumes  the  colour  and  aspect  of  the 
native  sulphide.  This  remarkable  change  probably  indicates  a  passage  from 
the  amorphotrs  to  the  crystalline  condition. 

When  powdered  tersulphide  of  antimony  is  boiled  in  a  solution  of  caustic 
potassa,  it  is  dissolved,  teroxide  of  antimony  and  sulphide  of  potassium  being 
produced.  The  latter  unites  with  an  additional  quantity  of  tersulphide  of 
antimony  to  a  soluble  sulphur-salt,  in  which  the  sulphide  of  potassium  is  the 
Bulphur-base,  and  the  tersulphide  of  antimony  is  the  sulphur-acid. 

{3  eq.  potassium  ^      f  3  eq.  sulphide  of 

^^.----''''^  \  potassium. 

3  eq.  oxygen  ^-^-^.^--^^-^^^"'^ 

Tersulphide    of   f  3  eq.  sulphur  ^     ~-~ — __^  .         . ,        ^ 

antimony  1  1  eq.  antimony  ""^^   ^^-    teroxide    of 

antimony. 

The  teroxide  of  antimony  separates  in  small  crystals  from  the  boiling  solu- 
tion when  the  latter  is  concentrated,  and  the  stflphur-salt  dissolves  an  extra 
proportion  of  tersulphide  of  antimony,  which  it  again  deposits  on  cooling  as 
a  red  amorphous  powder,  containing  a  small  admixture  of  teroxide  of  anti- 
mony and  sulphide  of  potassium.  This  is  the  kermes  mineral  of  the  old 
chemists.  The  filtered  solution  mixed  with  an  acid  gives  a  salt  of  potassa, 
sulphuretted  hydrogen,  and  precipitated  tersulphide  of  antimony.  Kermes 
may  also  be  made  by  fusing  a  mixture  of  5  parts  tersulphide  of  antimony 
and  3  of  dry  carbonate  of  soda,  boiling  the  mass  in  80  parts  of  water,  and 
filtering  while  hot;   the  compound  separates  on  cooling. 

Pentasulphide  of  antimony,  SbSg,  formerly  called  sulphur  auratum,  also 
exists ;  it  is  a  sulphur-acid.  18  parts  finely  powdered  tersulphide  of  anti- 
mony, 17  parts  dry  carbonate  of  soda,  13  parts  lime  in  the  state  of  hydrate, 
and  3 J  parts  sulphur,  are  boiled  for  some  hours  in  a  quantity  of  water;  car- 
bonate of  lime,  antimonate  of  soda,  pentasulphide  of  antimony,  and  sulphide 
of  sodium  are  produced.  The  first  is  insoluble,  and  the  second  partially  so ; 
the  two  last-named  bodies,  on  the  contrary,  unite  to  a  soluble  sulphur-salt, 
which  may  by  evaporation  be  obtained  in  beautiful  crystals.  A  solution  of  • 
this  substance,  mixed  with  dilute  sulphuric  acid,  furnishes  sulphate  of  soda, 
sulphuretted  hydrogen,  and  pentasulphide  of  antimony,  which  falls  as  a 
golden-yellow  flocculent  precipitate. 

Antimonetted  hydrogen. — A  compound  of  antimony  and  hydrogen  exists, 
out  has  not  been  isolated ;  when  zinc  is  put  into  a  solution  of  teroxide  of 
antimony,  and  sulphuric  acid  added,  part  of  tlie  hydrogen  combines  with  the 
26 


290  TELLURIUM. 

antimony.  This  gas  burns  with  a  greenish  flame,  giving  rise  to  white  fumei 
of  teroxide  of  antimony.  When  the  gas  is  conducted  through  a  red-hot  glass 
tube  of  narrow  dimensions,  or  burned  with  a  limited  supply  of  air,  such  as 
is  the  case  when  a  cold  porcelain  surface  is  pressed  into  the  flame,  metallio 
antimony  is  deposited. 

The  few  salts  of  antimony  soluble  in  water  are  amply  characterized  by 
the  orange  or  brick-red  precipitate  with  sulphuretted  hydrogen,  which  is 
soluble  in  solution  of  sulphide  of  ammonium,  and  again  precipitated  by  an 
acid. 

Besides  its  application  to  medicine,  antimony  is  of  great  importance  in  the 
arts  of  life,  inasmuch  as  it  forms  with  lead  type-metal.  This  alloy  expands 
at  the  moment  of  solidifying,  and  takes  an  exceedingly  sharp  impression  of 
the  mould.  It  is  remarkable  that  both  its  constituents  shrink  under  similar 
circumstances,  and  make  very  bad  castings.  Tersulphide  of  antimony  enters 
into  the  comnosition  of  the  blue  signal-light,  used  at  sea.* 

TELLURIUM. 

This  metal,  or  semi-metal,  is  of  very  rare  occurrence ;  it  is  found  in  a  few 
scarce  minerals  in  association  with  silver,  lead,  and  bismuth,  apparently 
replacing  sulphur,  and  is  most  easily  extracted  from  the  sulpho-telluride  of 
bismuth  of  Chemnitz,  in  Hungary.  The  finely  powdered  ore  is  mixed  with 
an  equal  weight  of  dry  carbonate  of  soda,  the  mixture  made  into  a  paste 
with  oil,  and  heated  to  whiteness  in  a  closely  covered  crucible.  Telluride 
and  sulphide  of  sodium  are  produced,  and  metallic  bismuth  set  free.  The 
fused  mass  is  dissolved  in  water  and  the  solution  freely  exposed  to  the  air, 
when  the  sodium  and  sulphur  oxidize  to  caustic  soda  and  hyposulphite  of 
soda,  while  the  tellurium  separates  in  the  metallic  state.  Tellurium  has  the 
colour  and  lustre  of  silver ;  by  fusion  and  slow  cooling  it  may  be  made  to 
exhibit  the  form  of  rhombohedral  crystals  similar  to  those  of  antimony  and 
arsenic.  It  is  brittle,  and  a  comparatively  bad  conductor  of  heat  and  elec- 
tricity ;  it  has  a  density  of  6-26,  melts  at  a  little  below  red-heat,  and  vola- 
tilizes at  a  higher  temperature.  Tellurium  burns  when  heated  in  the  air, 
and  is  oxidized  by  nitric  acid.  Two  compounds  of  this  substance  with 
oxygen  are  known,  having  acid  properties ;  they  much  resemble  the  acids 
of  arsenic. 

The  equivalent  of  tellurium  is  64-2 ;  its  symbol  is  Te. 

Tellurous  acid,  TeOj. — This  is  obtained  by  burning  tellurium  in  the  air, 
or  by  heating  it  in  fine  powder  with  nitric  acid  of  1-25  specific  gravity;  a 
solution  is  rapidly  formed,  from  which  white  anhydrous  octahedral  crystals 
of  tellurous  acid  are  deposited  on  standing.  The  acid  is  fusible  at  a  red- 
heat,  and  slightly  volatile  at  a  higher  temperature ;  it  is  but  feebly  soluble 
in  water  or  acids,  easily  dissolved  by  alkalis,  and  reduced  when  heated  with 
carbon  or  hydrogen.  A  hydrate  of  tellurous  acid  is  thrown  down  when 
tellurite  of  potassa  is  mixed  with  a  slight  excess  of  nitric  acid;  it  is  a  white 
powder,  soluble  to  a  certain  extent  in  water,  and  reddens  litmus. 

Telluric  acid,  TeO,.  —  Equal  parts  of  tellurous  acid  and  carbonate  of 
soda  are  fused,  and  the  product  dissolved  in  water ;  a  little  hydrate  of  soda 
is  added,  and  a  stream  of  chlorine  passed  through  the  solution.  The  liquid 
is  next  saturated  with  ammonia,  and  mixed  with  solution  of  chloride  of 
barium,  by  which  a  white  insoluble  precipitate  of  tellurite  of  baryta  is  thrown 
down.    This  is  washed  and  digested  vnth  a  quarter  of  its  weight  of  sulphuric 

*  Blue  or  Bengal  light:  — 

Dry  nitrate  of  potassa 6  parts. 

Sulphur 2      " 

Tersulphide  of  antimony 1      " 

All  in  flue  powder  and  intimately  mixed. 


ARSENIC.  291 

acid,  diluted  with  water.  The  filtered  solution  gives,  on  evaporation  in  the 
air,  large  crystals  of  telluric  acid. ' 

Telluric  acid  is  freely,  although  slowly,  soluble  in  water ;  it  has  a  metallic 
taste,  and  reddens  litmus-paper.  When  the  crystals  are  strongly  heated, 
they  lose  water,  and  yield  anhydrous  acid,  which  is  then  insoluble  in  water, 
and  even  in  a  boiling  alkaline  liquid.  At  the  temperature  of  ignition,  telluric 
acid  loses  oxygen,  and  passes  into  tellurous  acid.  The  salts  of  the  alkalis 
are  soluble,  but  do  not  crystallize ;  those  of  the  earths  are  nearly,  or  quite, 
insoluble. 

There  are  two  chlorides  of  tellurium,  and  also  a  hydride,  which  closely 
resembles  sulphuretted  hydrogen. 


Arsenic  is  sometimes  found  native ;  it  occurs  in  considerable  quantity  as  j^^ 
constituent  of  many  minerals,  combined  with  metals,  sulphur  and  oxygen. 
In  the  oxidized  state  it  has  been  found  in  very  minute  quantity  in  a  great 
many  mineral  waters.  The  largest  proportion  is  derived  from  the  roasting 
of  natural  arsenides  of  iron,  nickel,  and  cobalt ;  the  operation  is  conducted 
in  a  reverberatory  furnace,  and  the  volatile  products  condensed  in  a  long  and 
nearly  horizontal  chimney,  or  in  a  kind  of  tower  of  brickwork,  divided  into 
numerous  chambers.  The  crude  arsenious  acid  thus  produced  is  purified  by 
sublimation,  and  then  heated  with  charcoal  in  a  retort ;  the  metal  is  reduced, 
and  readily  sublimes. 

Arsenic  has  a  steel-grey  colour,  and  high  metallic  lustre  ;  it  is  crystalline 
and  very  brittle ;  it  tarnishes  in  the  air,  but  may  be  preserved  unchanged  in 
pure  water.  Its  density  is  5-7  to  5-9.  When  heated,  it  volatilizes  without 
fusion,  and,  if  air  be  present,  oxidizes  to  arsenious  acid.  The  vapour  has 
the  odour  of  garlic.  This  substance  combines  with  metals  in  the  same 
manner  as  sulphur  and  phosphorus,  which  it  resembles,  especially  the  latter, 
in  many  respects.  With  oxygen  it  unites  in  two  proportions,  giving  rise  to 
arsenious  and  arsenic  acids.     There  is  no  basic  oxide  of  arsenic. 

The  equivalent  of  arsenic  is  75 ;  it  symbol  is  As. 

Arsenious  acid  ;  white  oxide  of  arsenic  ;  AsOg.  —  The  origin  of  this 
substance  is  mentioned  above.  It  is  commonly  met  with  in  the  form  of  a 
heavy,  white,  glassy-looking  substance,  with  smooth  conchoidal  fracture, 
which  has  e-vndently  undergone  fusion.  When  freshly  prepared,  it  is  often 
transparent,  but  by  keeping  becomes  opaque,  at  the  same  time  slightly 
diminishing  in  density,  and  acquiring  a  greater  degree  of  solubility  in  water. 
100  parts  of  that  liquid  dissolve  at  212°  (100°C),  about  11-5  parts  of  the 
opaque  variety ;  the  largest  portion  separates,  however,  on  cooling,  leaving 
about  3  parts  dissolved ;  the  solution  feebly  reddens  litmus.  Cold  water, 
agitated  with  powdered  arsenious  acid,  takes  up  a  still  smaller  quantity. 
Alkalis  dissolve  this  substance  freely,  forming  arsenites;  also  compounds 
with  ammonia,  baryta,  strontia,  lime,  magnesia,  and  oxide  of  manganese, 
have  been  formed ;  it  is  also  easily  soluble  in  hot  hydrochloric  acid.  The 
vapour  of  arsenious  acid  is  colourless  and  inodorous ;  it  crystallizes  on  solidi- 
fying in  brilliant  transparent  octahedrons.  The  acid  itself  has  a  feeble 
sweetish  and  astringent  taste,  and  is  a  most  fearful  poison.' 

'  The  best  antidote  for  arsenious  acid  is  the  hydrate  of  the  red  oxide  of  iron.  In  its  recently 
precipitated  gelatinous  condition,  it  is  most  active.  It  acts  by  forming  an  insoluble  arseniato 
of  the  protoxide  of  iron;  for  the  peroxide  is  reduced  to  protoxide  by  losing  oxygen,  which, 
parsing  to  the  areeaious  acid,  forms  arsenic  acid.  This  change  is  represented  by  the  following 
formula, 

2  FeaOs  and  AsOs  =  4  FeO  +  AsOb. 

The  hydrate  is  incapable  of  decomposing  the  arsenites.  The  red  oxide,  to  act  as  an  antidote 
to  the  arsenical  salts,  requires  to  be  combined  with  an  acid,  which  may  separate  the  base,  and 


292  ARSENIC. 

Absenic  acid,  AsOg. — Powdered  arsenious  acid  is  dissolved  in  hot  hydro- 
chloric acid,  and  oxidized  by  the  addition  of  nitric  acid,  the  latter  being 
added  as  long  as  red  vapours  are  produced ;  the  whole  is  then  cautiously 
evaporated  to  complete  dryness.  The  acid  thus  produced  is  white  and  an- 
hydrous. Put  into  water,  it  slowly  but  completely  dissolves,  giving  a  highly 
acid  solution,  which,  on  being  evaporated  to  a  syrupy  consistence,  deposits, 
after  a  time,  hydrated  crystals  of  arsenic  acid.  When  strongly  heated,  it  is 
decomposed  into  arsenious  acid  and  oxygen  gas. 

This  substance  is  a  very  powerful  acid,  comparable  with  phosphoric,  which 
it  resembles  in  the  closest  manner,  forming  salts  strictly  isomorphous  with 
the  corresponding  phosphates  ;  it  is  also  tribasic.  An  arsenate  of  soda, 
2NaO,HO, AsOj  -f-  24HO,  indistinguishable  in  appearance  from  common  phos- 
phate of  soda,  may  be  prepared  by  adding  the  carbonate  to  a  solution  of  ar- 
senic acid,  until  an  alkaline  reaction  is  apparent,  and  then  evaporating. 
This  salt  also  crystallizes  with  14  equivalents  of  water.  Another  arsenate, 
SNaO.AsOg-f-  24HO,  is  produced  when  carbonate  of  soda  in  excess  is  fused 
with  arsenic  acid,  or  when  the  preceding  salt  is  mixed  with  caustic  soda.  A 
third,  NaO,2HO,As05-}-2HO,  is  made  by  substituting  an  excess  of  arsenic 
acid  for  the  solution  of  alkali.  The  alkaline  arsenates  which  contain  basic 
water  lose  the  latter  at  a  red-heat,  but  unlike  the  phosphates,  recover  it 
when  again  dissolved.'  The  salts  of  the  alkalis  are  soluble  in  water  ;  those 
of  the  earths  and  other  metallic  oxides  are  insoluble,  but  are  dissolved  by 
acids.  The  precipitate  with  nitrate  of  silver  is  highly  characteristic  of  arse- 
nic acid ;  it  is  reddish-brown. 

Three  Sulphides  of  Arsenic  are  known.  Realgar,  AsSg,  occurs  native ; 
it  is  formed  artificially,  by  heating  arsenic  acid  with  the  proper  proportion 
of  sulphur.  It  is  an  orange-red,  fusible,  and  volatile  substance,  employed 
in  painting  and  by  the  pyrotechnist  in  making  white-fire.  Orpiment,  AsSj, 
which  is  also  a  natural  product  of  the  mineral  kingdom,  is  made  by  fusing 
arsenic  acid  with  excess  of  sulphur,  or  by  precipitating  a  solution  of  the  acid 
by  sulphuretted  hydrogen.  It  is  a  golden-yellow  crystalline  substance,  fusi- 
ble and  volatile  by  heat.  A  higher  sulphide,  AsSg,  corresponding  to  arsenic 
acid,  is  produced  when  sulphuretted  hydrogen  is  transmitted  through  a  solu- 
tion of  arsenic  acid.  The  solution  of  arsenic  acid  is  not  immediately  pre- 
cipitated, the  pentasulphide  being  deposited  only  after  some  hours'  stand- 
ing. Its  precipitation  is  considerably  accelerated  by  ebullition.  It  is  a 
yellow  fusible  substance,  capable  of  sublimation.  Realgar,  orpiment,  and 
pentasulphide  of  arsenic  are  sulphur-acids. 

Arsenic  unites  with  chlorine,  iodine,  &c.  The  ierchloride,  AsClg,  is  formed 
by  distilling  a  mixture  of  1  part  of  arsenic,  and  G  parts  of  corrosive  subli- 
mate ;  it  is  a  colourless,  volatile  liquid,  decomposed  by  water  into  arseniousi 
and  hydrochloric  acids.  The  same  substance  is  produced,  with  disengage 
ment  of  heat  and  light,  when  powdered  arsenic  is  thrown  into  chlorine  gas. 
The  iodide,  Aslg,  is  formed  by  heating  metallic  arsenic  with  iodine ;  it  is  a 
deep  red  crystalline  substance,  capable  of  sublimation.  The  bromide  and 
fluoride  are  both  liquid. 

Arsenic  also  combines  with  hydrogen,  forming  a  gaseous  compound,  AsHg, 
analogous  to  phosphoretted  hydrogen.  It  is  obtained  pure  by  the  action  of 
strong  hydrochloric  acid  on  an  alloy  of  equal  parts  of  zinc  and  arsenic,  and 
is  produced  in  greater  or  less  proportion  whenever  hydrogen  is  set  free  in 

then  the  arsenious  acid  and  red  oxide  react  on  each  other  as  above.  The  acetate  of  the  red 
oxide  is  the  salt  used. 

Magnesia  has  also  been  recommended.  In  the  state  of  recently  precipitated  hydrate,  it  acts 
on  a  solution  of  arsenious  acid  with  nearly  the  same  rapidity  as  the  hydrated  peroxide  of 
iron.  In  the  condition  usually  found  in  the  shops,  it  cannot  be  depended  on  with  the  same 
Bertainty,  having  been  too  highly  calcined.  —  R.  B. 

*  Graham,  Elements,  p.  435. 


ARSENIC.  293 

contact  with  arsieuious  acid.  Arsenetted  hydrogen  is  a  colourless  gas,  of 
2-695  specific  gravity,  slightly  soluble  in  water,  and  having  the  smell  of  gar- 
lic. It  burns  when  kindled  with  a  blue  flame,  generating  aisenious  acid.  It 
is  also  decomposed  by  transmission  through  a  red-hot  tube.  Many  metallic 
solutions  are  precipitated  by  this  substance.  It  is,  when  inhaled,  exceed- 
ingly poisonous,  even  in  very  minute  quantity. 


Arsenious  acid  is  distinguished  by  characters  which  cannot  be  misunder- 
stood. 

Nitrate  of  silver,  mixed  with  a  solution  of  arsenious  acid  in  water,  occa- 
sions no  precipitate,  or  merely  a  faint  cloud ;  but  if  a  little  alkali,  as  a  drop 
of  ammonia,  be  added,  a  yellow  precipitate  of  arsenite  of  silver  immediately 
falls.  The  precipitate  is  exceedingly  soluble  in  excess  of  ammonia ;  that 
substance  must,  therefore,  be  added  with  great  caution ;  it  is  likewise  very 
soluble  in  nitric  acid. 

Sulphate  of  copper  gives  no  precipitation  with  solution  of  arsenious  acid, 
until  the  addition  has  been  made  of  a  little  alkali,  when  a  brilliant  yrilnfi^ 
green  precipitate  (Scheele's  green)  falls,  which  also  is  very  soluble  in  excess 
of  ammonia. 

Sulphuretted  hydrogen  passed  into  a  solution  of  arsenious  acid,  to  which 
a  few  drops  of  hydrochloric  or  sulphuric  acid  have  been  added,  occasions 
the  production  of  a  copious  bright  yellow  precipitate  of  orpiment,  which  is 
dissolved  with  facility  by  ammonia,  and  re-precipitated  by  acids. 

Solid  arsenious  acid,  heated  by  the  blow- 
pipe in  a  narrow  glass  tube  with  small  frag-  Fig.  150. 
ments  of  dry  charcoal,  affords  a  sublimate 
of  metallic  arsenic  in  the  shape  of  a  bril- 
liant steel-grey  metallic  ring.  A  portion  of 
this,  detached  by  the  point  of  a  knife  and 
heated  in  a  second  glass  tube,  with  access  of 
air,  yields,  in  its  turn,  a  sublimate  of  colour- 
less, transparent,  octahedral  crystals  of  ar- 
senious acid.     (Fig.  150,  magnified). 

All  these  experiments,  which  jointly  give 
demonstrative  proof  of  the  presence  of  the 
substance  in  question,  may  be  performed,  with 
perfect  precision  and  certainty,  upon  exceed- 
ingly small  quantities  of  material. 

The  detection  of  arsenious  acid  in  complex 
mixtures  containing  organic  matter  and  common  salt,  as  beer,  gruel,  soup, 
&c.,  or  the  fluid  contents  of  the  stomach  in  cases  of  poisoning,  is  a  very  far 
more  difficult  problem,  but  one  which  is,  unfortunately,  often  required  to  be 
solved.  These  organic  matters  interfere  completely  with  the  liquid  tests, 
and  render  their  indications  worthless.  Sometimes  the  difficulty  may  be 
eluded  by  a  diligent  search  in  the  suspected  liquid,  and  in  the  vessel  con- 
taining it,  for  fragments  or  powder  of  solid  arsenious  acid,  which,  from  the 
small  degree  of  solubility,  often  escape  solution,  and  from  the  high  density 
of  the  substance  may  be  found  at  the  bottom  of  the  vessels  in  which  the 
fluids  are  contained.  If  anything  of  the  kind  be  found,  it  may  be  washed 
by  decantation  with  a  little  cold  water,  dried,  and  then  reduced  with  char- 
coal. For  the  latter  purpose,  a  small  glass  tube  is  taken,  having  the  figure 
represented  in  the  margin ;  white  German  glass,  free  from  lead,  is  to  be 
preferred.  The  arsenious  acid,  or  what  is  suspected  to  be  such,  is  dropped 
to  the  bottom,  and  covered  with  splinters  or  little  fragments  of  charcoal, 
25* 


294 


ARSENIC. 


Fig.  151.  the  tube  being  filled  to  the  shoulder.  The  whole  is  gently 
heated,  to  expel  any  moisture  that  may  be  present  in  the  char- 
coal, and  the  deposited  water  wiped  from  the  interior  of  the 
tube  with  bibulous  paper.  The  narrow  part  of  the  tube  con- 
taining the  charcoal,  from  a  to  6,  (fig.  151),  is  now  heated  by 
the  blowpipe  flame ;  when  red-hot,  the  tube  is  inclined,  so  that 
the  bottom  also  may  become  heated.  The  arsenious  acid,  if 
present,  is  vaporized,  and  reduced  by  the  charcoal,  and  a  ring 
of  metallic  arsenic  deposited  on  the  cool  part  of  the  tube. 
To  complete  the  experiment,  the  tube  may  be  melted  at  a  by 
the  point  of  the  flame,  drawn  ofl",  and  closed,  and  the  arsenic 
oxidized  to  arsenious  acid,  by  chasing  it  up  and  down  by  the 
heat  of  a  small-spirit-lamp.  A  little  water  may  afterwards 
be  introduced,  and  boiled  in  the  tube,  by  which  the  arsenious 
acid  will  be  dissolved,  and  to  this  solution  the  tests  of  nitrate 
of  silver  and  ammonia,  sulphate  of  copper  and  ammonia,  and 
sulphuretted  hydrogen,  may  be  applied. 

When  the  search  for  solid  arsenious  acid  fails,  the  liquid 
itself  must  be  examined ;  a  tolerably  limpid  solution  must  be 
obtained,  from  which  the  arsenic  may  be  precipitated  by 
sulphuretted  hydrogen,  and  the  orpiment  collected,  and  reduced  to  the 
metallic  state.  It  is  in  the  first  part  of  this  operation  that  the  chief  diffi- 
culty is  found ;  such  organic  mixtures  refuse  to  filter,  or  filter  so  slowly, 
as  to  render  some  method  of  acceleration  indispensable.  Boiling  with  a 
little  caustic  potassa  or  acetic  acid  will  sometimes  efi"ect  this  object.  The 
following  is  an  outline  of  a  plan,  which  has  been  found  successful  in  a 
variety  of  cases,  in  which  a  very  small  quantity  of  arsenious  acid  had  been 
purposely  added  to  an  organic  mixture.  Oil  of  vitriol,  itself  perfectly  free 
from  arsenic,  is  mixed  with  the  suspected  liquid,  in  the  proportion  of 
about  a  measured  ounce  to  a  pint,  having  been  previously  diluted  with 
a  little  water,  and  the  whole  is  boiled  in  a  flask  for  half  an  hour,  or  until 
a  complete  separation  of  solid  and  liquid  matter  becomes  manifest.  The 
acid  converts  any  starch  that  may  be  present  into  dextrin  and  sugar; 
it  coagulates  completely  albuminous  substances,  and  casein,  in  the  case  of 
milk,  and  brings  the  whole  in  a  very  short  time  into  a  state  in  which  filtra- 
tion is  both  easy  and  rapid.  Through  the  filtered  solution,  when  cold,  a 
current  of  sulphuretted  hydrogen  is  transmitted,  and  the  liquid  is  warmed, 
to  facilitate  the  deposition  of  the  tersulphide,  which  falls  in  combination 
with  a  large  quantity  of  organic  matter,  which  often  communicates  to  it  a 
dirty  colour.  This  is  collected  upon  a  small  filter,  and  washed.  It  is  next 
transferred  to  a  capsule,  and  heated  with  a  mixture  of  nitric  and  hydro- 
chloric acids,  by  which  the  organic  impurities  are  in  a  great  measure  de- 
stroyed, and  the  arsenic  oxidized  to  arsenic  acid.  The  solution  is  evaporated 
to  dryness,  the  soluble  part  taken  up  by  dilute  hydrochloric  acid,  and  then 
the  solution  saturated  with  sulphurous  acid,  whereby  the  arsenic  acid  is  re- 
duced to  the  state  of  arsenious  acid,  the  sulphui'ous  being  oxidized  to  sul- 
phuric acid  ;  the  solution  of  arsenious  acid  may  be  precipitated  by  sulphu- 
retted hydrogen  without  any  difficulty.  The  liquid  is  warmed,  and  the  pre- 
cipitate washed  by  decantation,  and  dried.  It  is  then  mixed  with  black-flux, 
and  heated  in  a  small  glass  tube,  similar  to  that  already  described,  with 
similar  precautions ;  a  ring  of  reduced  arsenic  is  obtained,  which  may  be 
oxidized  to  arsenious  acid,  and  farther  examined.  The  black-flux  is  a  mix- 
ture of  carbonate  of  potassa  and  charcoal,  obtained  by  calcining  cream  of 
tartar  in  a  close  crucible  ;  the  alkali  transforms  the  sulphide  into  arsenious 
acid,  the  charcoal  subsequently  effecting  the  deoxidation.     A  mixture  of 


ARSENIC. 


2Sh 


Fig.  152. 


anhydrous  carbonate  of  soda  and  charcoal  may  be  substituted  with  advan- 
tage for  the  common  black-flux,  as  it  is  less  hygroscopic' 

Other  methods  of  proceeding,  different  in  principle  from  the  foregoing, 
have  been  proposed,  as  that  of  the  late  Mr.  Marsh,  which  is  exceedingly 
delicate.  The  suspected  liquid  is  acidulated  with  sulphuric  acid  and  placed 
in  contact  with  metallic  zinc ;  the  hydrogen  reduces  the  arsenious  acid  and 
combines  with  the  arsenic,  if  any  be  present.  The  gas  is  burned  at  a  jet, 
and  a  piece  of  glass  or  porcelain  held  in  the  flame,  when  any  admixture  of 
arsenetted  hydrogen  is  at  once  known  by  the  production  of  a  brilliant  black 
metallic  spot  of  reduced  arsenic  on  the  porcelain. 

It  has  been  observed  (page  290)  that  antimonetted  hydrogen  gives  a  simi- 
lar result.  In  order  to  distinguish  the  two  substances,  the  gas  may  be 
passed  into  a  solution  of  nitrate  of  silver.  Both  gases  give  rise  to  a  black 
precipitate,  which  in  the  case  of  antimonetted  hydrogen  consists  of  antimo- 
nide  of  silver,  Agg  Sb,  whilst  it  is  pure  silver  in  the  case  of  arsenetted  hy- 
drogen, the  arsenic  being  then  converted  into  arsenious  acid,  which  combines 
with  a  portion  of  oxide  of  silver.  The  arsenite  of 
silver  remains  dissolved  in  the  nitric  acid  which  is  li- 
berated by  the  precipitation  of  the  silver,  and  may 
be  thrown  down  with  its  characteristic  yellow  colour 
by  adding  ammonia  to  the  liquid  filtered  off  from  the 
black  precipitate. 

A  convenient  form  of  Marsh's  instrument  is  that 
shown  in  fig.  152,  it  consists  of  a  bent  tube,  having 
two  bulbs  blown  upon  it,  fitted  with  a  stop-cock  and 
narrow  jet.  Slips  of  zinc  are  put  into  the  lower  bulb, 
which  is  afterwards  filled  with  the  liquid  to  be  ex- 
amined. Ou  replacing  the  stop-cock,  closed,  the  gas 
collects  and  forces  the  fluid  into  the  upper  bulb, 
which  then  acts  by  its  hydrostatic  pressure  and  ex- 
pels the  gas  through  the  jet  as  soon  as  the  stop-cock  is 
opened.  It  must  be  borne  in  mind  that  both  common 
zinc  and  sulphuric  acid  ofteu  cojitain  traces  of  arsenic.^ 

A  slip  of  copper  foil  boiled  in  the  poisoned  liquid, 
previously  acidulated  with  hydrochloric  acid,  with- 
draws the  arsenic  and  becomes  covered  with  a  white 
alloy.  By  heating  the  metal  in  a  glass  tube,  the 
arsenic  is  expelled,  and  oxidized  to  arsenious  acid. 


*  See  a  paper  by  the  author  on  the  detection  of  arsenic.    Pharmaceutical  Journal,  i.  514. 

'  Where  the  amount  of  arsenic  present  is  small,  it  becomes  necessary  to  take  advantage  of 
the  effects  of  heat,  and  cause  the  gas  to  pass  slowly  through  a  red-hot  tube  until  all  the  zinc 
is  dissolved.  The  reduced  arsenic  will  be  deposited  on  the  cool  part  of  the  tube  ju.st  beyond 
the  heated  portion.  In  all  cases  of  using  the  above  test,  it  is  necessary  to  ascertain  the  purity 
of  the  zinc  and  acid  by  trial,  previous  to  addition  of  the  suspected  liijuid. — R.  B. 


296  SILVER 


SECTION   VI. 
METALS  WHOSE  OXIDES  ARE  REDUCEI  BY  HEAT. 


Silver  is  found  in  the  metallic  state,  in  union  with  sulphur,  and  also  as 
chloride  and  bromide.  Among  the  principal  silver  mines  may  be  mentioned 
those  of  the  Hartz  mountains  in  Germany,  of  Kongsberg  in  Norway,  and, 
more  particularly,  of  the  Andes  in  both  North  and  South  America. 

The  greater  part  of  the  silver  of  commerce  is  extracted  from  ores  so  poor 
as  to  render  any  process  of  smelting  or  fusion  inapplicable,  even  where  fuel 
could  be  obtained,  and  this  is  often  difficult  to  be  procured.  Recourse,  there- 
fore, is  had  to  another  method,  that  of  amalyamation,  founded  on  the  easy 
solubility  of  silver  and  many  other  metals  in  metallic  mercury. 

The  amalgamation-process,  as  conducted  in  Germany,  differs  somewhat 
from  that  in  use  in  America.  The  ore  is  crushed  to  powder,  mixed  with  a 
quantity  of  common  salt,  and  roasted  at  a  low  red-heat  in  a  suitable  furnace, 
by  which  treatment  any  sulphide  of  silver  it  may  contain  is  converted  into 
chloride.  The  mixture  of  earthy  matter,  oxides  of  iron,  copper,  soluble 
salts,  chloride  of  silver,  and  metallic  silver,  is  sifted  and  put  into  large  bar- 
rels, made  to  revolve  on  axes,  with  a  quantity  of  water  and  scraps  of  iron, 
and  the  whole  agitated  together  for  some  time,  during  which  the  iron  reduces 
the  chloride  of  silver  to  the  state  of  metal.  A  certain  proportion  of  mer- 
cury is  then  introduced,  and  the  agitation  repeated ;  the  mercury  dissolves 
out  the  silver,  together  with  gold,  if  there  be  any,  metallic  copper,  and  other 
substances,  forming  a  fluid  amalgam  easily  separable  from  the  thin  mud  of 
earthy  matter  by  subsidence  and  washing.  This  amalgam  is  strained 
through  strong  linen  cloth,  and  the  solid  portion  exposed  to  heat  in  a  kind 
of  retort,  by  which  the  remaining  mercury  is  distilled  off  and  the  silver  left 
behind  in  an  impure  condition. 

A  considerable  quantity  of  silver  is  obtained  from  argentiferous  galena ; 
in  fact,  almost  every  specimen  of  native  sulphide  of  lead  will  be  found  to 
contain  traces  of  this  metal.  When  the  proportion  rises  to  a  certain  amount 
it  becomes  worth  extracting.  The  ore  is  reduced  in  the  usual  manner,  the 
whole  of  the  silver  remaining  with  the  lead ;  the  latter  is  then  re-melted  in 
a  large  vessel,  and  allowed  slowly  to  cool  until  solidification  commences. 
The  portion  which  first  crystallizes  is  nearly  pure  lead,  the  alloy  with  silver 
being  more  fusible  than  lead  itself;  by  particular  management  this  is  drained 
away,  and  found  to  contain  nearly  the  whole  of  the  silver.  This  rich  mass 
is  next  exposed  to  a  red-heat  on  the  shallow  hearth  of  a  furnace,  while  a 
stream  of  air  is  allowed  to  impinge  upon  its  surface ;  oxidation  takes  place 
with  great  rapidity,  the  fused  oxide  or  litharge  being  constantly  swept  from 
the  metal  by  the  blast.  When  the  greater  part  of  the  lead  has  been  thus 
removed,  the  residue  is  transferred  to  a  cvpel  or  shallow  dish  made  of  bone- 
ashes,  and  again  heated ;  the  last  of  the  lead  is  now  oxidized,  and  the  oxide 


SILVER 


2^'7' 


sinks  in  a  melted  state  into  the  porous  vessel,  wliile  the  silver,  almost  che- 
mically pure,  and  exhibiting  a  brilliant  surface,  remains  behind. 

Pure  silver  may  be  easily  obtained.  The  metal  is  dissolved  in  nitric  acid; 
if  it  contains  copper,  the  solution  will  have  a  blue  tint ;  gold  will  remain  un- 
dissolved as  a  black  powder.  The  solution  is  mixed  with  hydrochloric  acid 
or  with  common  salt,  and  the  white,  insoluble  curdy  precipitate  of  chloride 
of  silver  washed  and  dried.  This  is  then  mixed  with  about  twice  its  weight 
of  anhydrous  carbonate  of  soda,  and  the  mixture,  placed  in  an  earthen  cru- 
cible, gradually  raised  to  a  temperature  approaching  whiteness,  during 
which  the  carbonate  of  soda  and  the  chloride  react  upon  each  other,  carbonic 
acid  and  oxygen  escape,  while  metallic  silver  and  chloride  of  sodium  result ; 
the  former  fuses  into  a  button  at  the  bottom  of  the  crucible,  and  is  easily 
detached. 

Pure  silver  has  a  most  perfect  white  colour,  and  a  high  degree  of  lustre ; 
it  is  exceedingly  malleable  and  ductile,  and  is  probably  the  best  conductor 
both  of  heat  and  electricity  known.  Its  specific  gravity  is  10-5.  In  hardness 
it  lies  between  gold  and  copper.  It  melts  at  a  bright  red-heat,  about  1873° 
(1023°C),  according  to  the  observations  of  Mr.  Daniell.  Silver  is  inalterable 
by  air  and  moisture  ;  it  refuses  to  oxidize  at  any  temperature,  but  possesses 
the  extraordinary  faculty,  already  noticed  in  an  earlier  part  of  the  work,  of 
absorbing  many  times  its  volume  of  oxygen  when  strongly  heated  in  an  at- 
mosphere of  that  gas,  or  in  common  air.  This  oxygen  is  again  disengaged 
at  the  moment  of  solidification,  and  gives  rise  to  the  peculiar  arborescent 
appearance  often  remarked  on  the  surface  of  masses  or  buttons  of  pure 
silver.  The  addition  of  2  per  cent,  of  copper  is  sufficient  to  prevent  this 
absorption  of  oxygen.  Silver  oxidizes  when  heated  with  fusible  siliceous 
matter,  as  glass,  which  it  stains  yellow  or  orange,  from  the  formation  of  a 
silicate.  It  is  little  attacked  by  hydrochloric  acid ;  boiling  oil  of  vitriol  con- 
verts it  into  sulphate  with  evolution  of  sulphurous  acid ;  and  nitric  acid, 
even  dilute  and  in  the  cold,  dissolves  it  readily.  The  tarnishing  of  surfaces 
of  silver  exposed  to  the  air  is  due  to  sulphuretted  hydrogen,  the  metal  having 
a  strong  attraction  for  sulphur.  There  are  three  oxides  of  silver,  one  of 
which  is  a  powerful  base  isomorphous  with  potassa,  soda,  and  oxide  if  am- 
monium. 

The  equivalent  of  silver  is  108 ;  its  symbol  is  Ag  (argentum). 

Suboxide  op  silver,  AggO. — When  dry  citrate  of  silver  is  heated  to  212° 
(100°C)  in  a  stream  of  hydrogen  gas,  it  loses  oxygen  and  becomes  dark 
brown.  The  product  dissolved  in  water,  gives  a  dark-coloured  solution  con- 
taining free  citric  acid  and  citrate  of  the  suboxide  of  silver.  The  suboxide 
is  then  precipitated  by  potassa.  It  is  a  black  powder,  very  easily  decom- 
posed, and  soluble  in  ammonia.  The  solution  of  citrate  is  rendered  colourless 
by  heat,  being  resolved  into  a  salt  of  the  protoxide  and  metallic  silver. 

Protoxide  of  silver,  AgO.  —  Caustic  potassa  added  to  a  solution  of 
nitrate  of  silver  throws  down  a  pale-brown  precipitate,  which  consists  of 
protoxide  of  silver.  It  is  very  soluble  in  ammonia,  and  is  dissolved  also  to 
a  small  extent  by  pure  water;  the  solution  is  alkaline.  Recently  precipitated 
chloride  of  silver,  boiled  in  a  solution  of  caustic  potassa  of  specific  gravity 
1-25,  according  to  the  observation  of  Dr.  Gregory,  is  converted,  although 
with  difficulty,  into  oxide  of  silver,  which  in  this  case  is  black  and  very  dense. 
The  protoxide  of  silver  neutralizes  acids  completely,  and  forms,  for  the  most 
part,  colourless  salts.  It  is  decomposed  by  a  red-heat,  with  extrication  of 
oxygen,  spongy  metallic  silver  being  left ;  the  sun's  rays  also  effect  its  de- 
composition to  a  small  extent. 

Peroxide  of  silver.  —  This  is  a  black  crystalline  substance  which  forms 
upon  the  positive  electrode  of  a  voltaic  arrangement  employed  to  decompose 
a  solution  of  nitrate  of  silver.     It  is  reduced  by  heat,  evolves  chlorine  when 


298  SILVER. 

acted  upon  by  hydrochloric  acid,  explodes  when  mixed  with  phosphorus  and 
struck,  and  decomposes  solution  of  ammonia  with  great  energy  and  rapid 
disengagement  of  nitrogen  gas. 

Nitrate  of  silver,  AgOjNOj. — The  nitrate  is  prepared  by  directly  dis- 
solving silver  in  nitric  acid  and  evaporating  the  solution  to  dryness,  or  until 
it  is  strong  enough  to  crystallize  on  cooling.  The  crystals  are  colourless, 
transparent,  anhydrous  tables,  soluble  in  an  equal  weight  of  cold,  and  in 
half  that  quantity  of  boiling  water ;  they  also  dissolve  in  alcohol.  They  fuse 
when  heated  like  those  of  nitre,  and  at  a  higher  temperature  suffer  decom- 
position ;  the  lunar  caustic  of  the  surgeon  is  nitrate  of  silver  which  has  been 
melted  and  poured  into  a  cylindrical  mould.  The  salt  blackens  when  exposed 
to  light,  more  particularly  if  organic  matters  of  any  kind  be  present,  and  is 
frequently  employed  to  communicate  a  dark  stain  to  the  hair ;  it  enters  into 
the  composition  of  the  "indelible"  ink  used  for  marking  linen.  The  black 
Btain  has  been  thought  to  be  metallic  silver ;  it  may  possibly  be  suboxide. 
Pure  nitrate  of  silver  may  be  prepared  from  the  metal  alloyed  with  copper : 
the  alloy  is  dissolved  in  nitric  acid,  the  solution  evaporated  to  dryness,  and 
the  mixed  nitrates  cautiously  heated  to  fusion.  A  small  portion  of  the  melted 
mass  is  removed  from  time  to  time  for  examination ;  it  is  dissolved  in  water, 
filtered,  and  ammonia  added  to  it  in  excess.  While  any  copper-salt  remains 
undecomposed,  the  liquid  will  be  blue,  but  when  that  no  longer  happens,  the 
nitrate  may  be  suffered  to  cool,  dissolved  in  water,  and  filtered  from  the  inso- 
luble black  oxide  of  copper. 

Sulphate  of  silver,  AgO,SOs.  —  The  sulphate  may  be  prepared  by  boil- 
ing together  oil  of  vitriol  and  metallic  silver,  or  by  precipitating  a  concen- 
trated solution  of  nitrate  of  silver  by  an  alkaline  sulphate.  It  dissolves  in 
88  parts  of  boiling  water,  and  separates  in  great  measure  in  a  crystalline 
form  on  cooling,  having  but  a  feeble  degree  of  solubility  at  a  low  tempera- 
ture. It  forms  a  crystallizable  compound  with  ammonia,  freely  soluble  in 
water,  containing  AgO,S03-f-2NH3. 

Hyposulphate  of  Silver,  AgO,Sg05-|-HO,  is  a  soluble  crystallizable  salt, 
permanent  in  the  air.  The  hyposulphite  is  insoluble,  white,  and  very  prone 
to  decomposition ;  it  combines  with  the  alkaline  hyposulphites,  forming  solu- 
ble compounds  distinguished  by  an  intensely  sweet  taste.  The  alkaline  hy- 
posulphites dissolve  both  oxide  and  chloride  of  silver,  and  give  rise  to  similar 
salts,  an  oxide  or  chloride  of  the  alkaline  metal  being  at  the  same  time 
formed.  Carbonate  of  silver  is  a  white  insoluble  substance  obtained  by  mix- 
ing solutions  of  nitrate  of  silver  and  of  carbonate  of  soda.  It  is  blackened 
and  decomposed  by  boiling. 

Chloride  of  silver,  AgCl. — This  substance  is  almost  invariably  produced 
when  a  soluble  salt  of  silver  and  a  soluble  chloride  are  mixed.  It  falls  as  a 
white  curdy  precipitate,  quite  insoluble  in  water  and  nitric  acid,  but  one 
part  of  chloride  of  sUver  is  soluble  in  200  parts  of  hydrochloric  acid  when 
concentrated,  and  in'about  600  parts  when  diluted  with  double  its  weight 
of  water.  When  heated  it  melts,  and  on  cooling  becomes  a  greyish  crystal- 
line mass,  which  cuiSs  like  horn ;  it  is  found  native  in  this  condition,  consti- 
tuting the  horn-silver  of  the  mineralogist.  Chloride  of  silver  is  decomposed 
by  light  both  in  a  dry  and  wet  state,  very  slowly  if  pure,  and  quickly  if  or- 
ganic matter  be  present:  it  is  reduced  also  when  put  into  water  with  metal- 
lic zinc  or  iron.  It  is  soluble  with  great  ease  in  ammonia  and  in  a  solution 
of  cyanide  of  potassium.  In  practical  analysis  the  proportion  of  chlorine 
or  hydrochloric  acid  in  a  compound  is  always  estimated  by  precipitation  by 
solution  of  silver.  The  liquid  is  acidulated  with  nitric  acid,  and  an  excess 
of  nitrate  of  silver  added ;  the  chloride  is  collected  on  a  filter,  or  better  by 
subsidence,  washed,  dried,  and  fused;  100  parts  correspend  to  24-7  of  chlo- 
rine, or  25-43  of  hydrochloric  acid. 


GOLD.  29^ 

Iodide  of  silver,  Agl.  —  The  iodide  is  a  pale  yellow  insoluble  precipitate 
produced  by  adding  nitrate  of  silver  to  iodide  of  potassium;  it  is  insoluble, 
or  nearly  so,  in  ammonia,  and  forms  an  exception  to  the  silver-salts  in  gene- 
ral in  "this  respect.  The  bromide  of  silver  vei'y  closely  resembles  the 
chloride. 

Sulphide  of  silver,  AgS. — This  is  a  soft,  grey,  and  somewhat  malleable 
substance,  found  native  in  a  crystallized  state,  and  easily  produced  by  melt- 
ing together  its  constituents,  or  by  precipitating  a  solution  of  silver  by  sul- 
phuretted hydrogen.  It  is  a  strong  sulphur-base,  and  combines  with  the 
sulphides  of  antimony  and  arsenic:  examples  of  such  compounds  are  found 
in  the  beautiful  minerals  dark  and  light  red  silver  ore. 

Ammonia  compound  of  silver  ;  Berthollet's  fulminatikq  silver.  — 
When  precipitated  oxide  of  silver  is  digested  in  ammonia,  a  black  substance 
is  produced,  possessing  exceedingly  dangerous  explosive  properties.  It 
explodes  while  moist  when  rubbed  with  a  hard  body,  but  when  dry  the  touch 
of  a  feather  is  sufficient.  The  ammonia  retains  some  of  this  substance  in 
solution,  and  deposits  it  in  small  crystals  by  spontaneous  evaporation.  A 
similar  compound  containing  oxide  of  gold  exists.  It  is  easy  to  understand 
the  reason  why  these  bodies  are  subject  to  such  violent  and  sudden  decom- 
position by  the  slightest  cause,  on  the  supposition  that  they  contain  an  oxide 
of  an  easily  reducible  metal  and  ammonia ;  the  attraction  between  the  two 
constituents  of  the  substance  is  very  feeble,  while  that  between  the  oxygen 
of  the  one  and  the  hydrogen  of  the  other  is  very  powerful.  The  explosion 
is  caused  by  the  sudden  evolution  of  nitrogen  gas  and  vapour  of  water,  the 
metal  being  set  free. 


A  soluble  salt  of  silver  is  perfectly  characterized  by  the  white  curdy  pre- 
cipitate of  chloride  of  silver,  darkening  by  exposure  to  light,  and  insoluble 
in  hot  nitric  acid,  which  is  produced  by  the  addition  of  any  soluble  chlo- 
ride. Lead  is  the  only  metal  which  can  be  confounded  with  it  in  this  re- 
spect, but  chloride  of  lead  is  soluble  to  a  great  extent  in  boiling  water,  and 
is  deposited  in  brilliant  acicular  crystals  when  the  solution  cools.  Solutions 
of  silver  are  reduced  to  the  metallic  state  by  iron,  copper,  mercury,  and  other 
metals. 

The  economical  uses  of  silver  are  many :  it  is  admirable  for  culinary  and 
other  similar  purposes,  not  being  attacked  in  the  slightest  degree  by  any 
of  the  substances  used  for  food.  It  is  necessai'y,  however,  in  these  cases 
to  diminish  the  softness  of  the  metal  by  a  small  addition  of  copper.  The 
standard  silver  of  England  contains  222  parts  of  silver  and  18  parts  of 
copper. 

gold. 

Gold,  in  small  quantities,  is  a  very  widely  diffused  metal ;  traces  are  con- 
stantly found  in  the  iron  pyrites  of  the  more  ancient  rocks.  It  is  always 
met  with  in  the  metallic  state,  sometimes  beautifully  crystallized  in  the  cubic 
form,  associated  with  quartz,  oxide  of  iron,  and  other  substances,  in  regular 
mineral  veins.  The  sands  of  various  rivers  have  long  furnished  gold  derived 
from  this  source,  and  separable  by  a  simple  process  of  washing ;  such  is  the 
gold-dust  of  commerce.  When  a  veinstone  is  wrought  for  gold,  it  is  stamped 
to  powder,  and  shaken  in  a  suitable  apparatus  with  water  and  mercury ;  an 
amalgam  is  formed,  which  is  afterwards  separated  from  the  mixture  and  de- 
composed by  distillation. 

The  pure  metal  is  obtained  by  solution  in  nitro-hydrochloric  &cid  and  pre- 
cipitation by  a  salt  of  protoxide  of  iron,  which,  by  undergoing  peroxidation, 


300  GOLD 

reduces  the  gold.     The  latter  falls  as  a  brown  powder,  which  acquu'es  the 
metallic  lustre  by  friction. 

Gold  is  a  soft  metal,  having  a  beautiful  yellow  colour.  It  surpasses  all 
other  metals  in  malleability,  the  thinnest  gold-leaf  not  exceeding,  it  is  said, 
2{F(jViny  ^^  ^^  ^^^^  ^^  thickness,  while  the  gilding  on  the  silver  wire  used  in 
the  manufacture  of  gold-lace  is  still  thinner.  It  may  also  be  drawn  into  very 
fine  wire.  Gold  has  a  density  of  19-5 ;  it  melts  at  a  temperature  a  little 
above  the  fusing-point  of  silver.  Neither  air  nor  water  aflFect  it  in  the  least 
at  any  temperature  ;  the  ordinary  acids  fail  to  attack  it,  singly.  A  mixture 
of  nitric  and  hydrochloric  acids  dissolves  gold,  however,  with  ease,  the  ac- 
tive agent  being  the  liberated  chlorine.  Gold  forms  two  compounds  with 
oxygen,  and  two  corresponding  compounds  with  chlorine,  iodine,  sulphur, 
&c.     Both  oxides  refuse  to  unite  with  acids. 

The  equivalent  of  gold  is  197.     Its  symbol  is  Au  (aurum). 
.  Pkotoxtde  of  gold,  AuO.  —  The  protoxide  is  produced  when  caustic  pq- 
tassa  in  solution  is  poured  upon  the  protochloride.     It  is  a  green  powder, 
partly  soluble  in  the  alkaline  liquid ;  the  solution  rapidly  decomposes  into 
metallic  gold,  which  subsides,  and  into  teroxide,  which  remains  dissolved. 

Teroxide  of  gold  ;  auric  acid  ;  AuOg. — When  magnesia  is  added  to  the 
terchloride  of  gold,  and  the  sparingly  soluble  aurate  of  that  base  well  washed 
and  digested  with  nitric  acid,  the  teroxide  is  left  as  an  insoluble  reddish- 
yellow  powder,  which,  when  dry,  becomes  chestnut-brown.  It  is  easily  re- 
duced by  heat,  and  also  by  mere  exposure  to  light ;  it  is  insoluble  in  oxygen 
acids  with  the  exception  of  strong  nitric  acid,  insoluble  in  hydrofluoric  acid, 
easily  dissolved  by  hydrochloric  and  hydrobromic  acids.  Alkalis  dissolve  it 
freely;  indeed,  the  acid  properties  of  this  substance  are  very  strongly 
marked  ;  it  partially  decomposes  a  solution  of  chloride  of  potassium  when 
boiled  with  that  liquid,  potassa  being  produced.  When  digested  with  ammo- 
nia, it  furnishes  fulminating  gold. 

Protochloride  of  gold,  AuCl.  —  This  substance  is  produced  when  the 
terchloride  is  evaporated  to  dryness  and  exposed  to  a  heat  of  440°  (226° -60) 
until  chlorine  ceases  to  be  exhaled.  It  forms  a  yellowish-white  mass,  inso- 
luble in  water.  In  contact  with  that  liquid  it  is  decomposed  slowly  in  the 
cold,  and  rapidly  by  the  aid  of  heat,  into  metallic  gold  and  terchloride. 

Terchloride  of  gold,  AuClg.  —  This  is  the  most  important  compound  of 
the  metal ;  it  is  always  produced  when  gold  is  dissolved  in  nitro-hydrochloric 
acid.  The  deep  yellow  solution  thus  obtained,yields,  by  evaporation,  yellow 
crystals  of  the  double  chloride  of  gold  and  hydrogen  ;  when  this  is  cautiously 
heated,  hydrochloric  acid  is  expelled,  and  the  residue,  on  cooling,  solidifies 
to  a  red  crystalline  mass  of  terchloride  of  gold,  very  deliquescent,  and  so- 
luble in  water,  alcohol,  and  ether.  The  terchloride  of  gold  combines  with  a 
number  of  metallic  chlorides,  forming  a  series  of  double  salts,  of  which  the 
general  formula  in  the  anhydrous  state  is  MCl-j-AuClgjM  representing  an 
equivalent  of  the  second  metal.  These  compounds  are  mostly  yellow  when 
in  crystals,  and  red  when  deprived  of  water. 

A  mixture  of  terchloride  of  gold  with  excess  of  bicarbonate  of  potassa  or 
Hoda  is  used  for  gilding  small  ornamental  articles  of  copper;  these  are 
cleaned  by  dilute  nitric  acid,  and  then  boiled  in  the  mixture  for  some  time, 
by  which  means  they  acquire  a  thin  but  perfect  coating  of  reduced  gold. 

The  other  compounds  of  gold  are  of  very  little  importance. 


The  presence  of  this  metal  in  solution  may  be  known  by  the  brown  pre- 
cipitate with  sulphate  of  protoxide  of  iron,  fusible  before  the  blowpipe  into 
a  bead  of  gold ;  and  by  the  purple  compound  formed  when  the  tei'chloride 
of  gold  is  added  to  a  solution  of  protochloride  of  tin. 


MERCURY,    OR    QUICKSILVER.  301 

Oold  intended  for  coin,  and  most  other  purposes,  is  always  alloyed  with  a 
certain  proportion  of  silver  or  copper,  to  increase  its  hardness  and  durability ; 
the  first  named  metal  confers  a  pale  greenish  colour.  English  standard  gold 
contains  yV  of  alloy,  now  always  copper.  Gold-leaf  is  made  by  rolling  out 
plates  of  pure  gold  as  thin  as  possible,  and  then  beating  them  between  folds 
of  membrane  by  a  heavy  hammer,  until  the  requisite  degree  of  tenuity  has 
been  reached.     The  leaf  is  made  to  adhere  to  wood,  &c.,  by  size  or  varnish. 

Gilding  on  copper  has  very  generally  been  performed  by  dipping  the  arti- 
cles into  a  solution  of  nitrate  of  mercury,  and  then  shaking  them  with  a 
small  lump  of  a  soft  amalgam  of  gold  with  that  metal,  which  thus  becomes 
spread  over  their  surfaces ;  the  articles  are  subsequently  heated  to  expel  the 
mercury  and  then  burnished.  Gilding  on  steel  is  done  either  by  applying  a 
solution  of  terchloride  of  gold,  in  ether,  or  by  roughening  the  surface  of  the 
metal,  heating  it,  and  applying  gold-leaf,  with  a  burnisher.  Gilding  by 
electrolysis — an  elegant  and  simple  method,  now  rapidly  superseding  many 
of  the  others — has  already  been  noticed.  The  solution  usually  employed  is 
obtained  by  dissolving  oxide  or  cyanide  of  gold  in  a  solution  of  cyanide  of 
potassium.' 

MEKCUEY,    OR   QUICKSILVEB. 

This  very  remarkable  metal  has  been  known  from  an  early  period,  and» 
perhaps  more  than  all  others,  has  excited  the  attention  and  curiosity  of  ex- 
perimenters, by  reason  of  its  peculiar  physical  properties.  Mercury  is  of 
great  importance  in  several  of  the  arts,  and  enters  into  the  composition  of 
many  valuable  medicaments. 

Metallic  mercury  is  occasionally  met  with  in  globules  disseminated  through 
the  native  sulphide,  which  is  the  ordinary  ore.  This  latter  substance, 
sometimes  called  cinnabar,  is  found  in  considerable  quantity  in  several 
localities,  of  which  the  most  celebrated  are  Almaden  in  New  Castile  and 
Idria  in  Carniola.  Only  recently  it  has  been  discovered  in  great  abundance, 
and  of  remarkable  purity,  in  California.  The  metal  is  obtained  by  heating 
the  sulphide  in  an  iron  retort  with  lime  or  scraps  of  iron,  or  by  roasting  it 
in  a  furnace,  and  conducting  the  vapours  into  a  large  chamber,  where  the 
mercury  is  condensed,  while  the  sulphurous  acid  is  allowed  to  escape. 
Mercury  is  imported  into  this  country  in  bottles  of  hammered  iron,  contain- 
ing seventy-five  pounds  each,  and  in  a  state  of  considerable  purity.  When 
purchased  in  smaller  quantities,  it  is  sometimes  found  adulterated  "with  tin 
and  lead,  which  metals  it  dissolves  to  some  extent  without  much  loss  of 
fluidity.  Such  admixture  may  be  known  by  the  foul  surface  the  mercury 
exhibits  when  shaken  in  a  bottle  containing  air,  and  by  the  globules,  when 
made  to  roll  upon  the  table,  having  a  train  or  tail. 

Mercury  has  a  nearly  silver-white  colour,  and  a  very  high  degree  of  lustre  ; 
It  is  liquid  at  all  ordinary  temperatures,  and  only  solidifies  when  cooled  to 
_  40°  (—  40°C),  In  this  state  it  is  soft  and  malleable.  At  662°  (350°C)  it 
boils,  and  yields  a  transparent,  colourless  vapour,  of  great  density.  The 
metal  volatilizes,  however,  to  a  sensible  extent  at  all  temperatures  above  68° 
<'20°C)  or  70°  (21°C) ;  below  this  point  its  volatility  is  imperceptible.  The 
volatility  of  mercury  at  the  boiling  heat  is  singularly  retarded  by  the  pre- 
sence of  minute  quantities  of  lead  or  zinc.  The  specific  gravity  of  mercur/ 
at  60°  (15°-5C)  is  13-59 ;  that  of  frozen  mercury  about  14,  great  contraction 
taking  place  in  the  act  of  solidification. 

Pure  quicksilver  is  quite  inaltera,ble  in  the  air  at  common  temperatures, 
but  when  heated  to  near  its  boiling  point  it  slowly  absorbs  oxygen,  and  be- 
comes converted  into  a  crystalline  dark  red  powder,  which  is  the  highest 

*  Messrs.  Elkington,  A;pplication  of  EIectro-M«tallurgy  to  the  Arts. 


802  MERCURY,    OR    QUICKSILVER. 

oxide.  At  a  dull  red-heat  this  oxide  is  again  decomposed  into  its  constituents. 
Hydrochloric  acid  has  little  or  no  action  on  mercury,  and  the  same  may  be 
said  of  sulphuWc  acid  in  a  diluted  state ;  when  the  latter  is  concentrated  and 
boiling  hot,  it  oxidizes  the  metal,  converting  it  into  sulphate  of  the  red  oxide, 
with  evolution  of  sulphurous  acid.  Nitric  acid,  even  dilute  and  in  the  cold, 
dissolves  mercury  freely,  with  an  evolution  of  binoxide  of  nitrogen. 

Mercury  combines  with  oxygen 'in  two  proportions,  forming  a  grey  and  a 
red  oxide,  both  of  which  are  salifiable.  As  the  salts  of  the  red  oxide  are 
the  most  stable  and  permanent,  that  substance  may  be  regargded  as  the  true 
protoxide,  instead  of  the  grey  oxide,  to  which  the  term  has  formerly  been 
applied.  Until,  however,  isomorphous  relations  connecting  mercury  with 
the  other  metals  shall  be  established,  the  constitution  of  the  two  oxides 
and  that  of  the  corresponding  chlorides,  iodides,  &c.,  must  remain  somewhat 
unsettled.' 

The  equivalent  of  mercury  on  the  above  supposition,  will  be  100;  its 
symbol  is  Hg  (hydrargyrum). 

Suboxide  of  mercury  ;  grey  oxide  ;  HgjO.  —  The  suboxide  is  easily 
prepared  by  adding  caustic  potassa  to  the  nitrate  of  this  substance,  or  by 
digesting  calomel  in  solution  of  caustic  alkali.  It  is  a  dark  grey,  nearly 
black,  heavy  powder,  insoluble  in  water.  It  is  slowly  decomposed  by  the 
action  of  light  into  metallic  mercury  and  red  oxide.  The  preparations  known 
in  pharmacy  by  the  names  blue  pill,  grey  ointment,  mercury  with  chalk,  &c., 
often  supposed  to  owe  their  efficacy  to  this  substance,  merely  contain  the 
finely  divided  metal. 

Protoxide  of  mercury  ;  red  oxide  ;  HgO. — There  are  numerous  methods 
by  which  this  method  may  be  obtained ;  the  following  may  be  cited  as  the 
most  important :  —  (1)  By  exposing  mercury  in  a  glass  flask,  with  a  long 
narrow  neck,  for  several  weeks  to  a  temperature  approaching  600°  (3 15° -50) ; 
the  prodjict  has  a  dark  red  colour  and  is  highly  crystalline ;  it  is  the  red 
precipitate  of  the  old  writers,  (2)  By  cautiously  heating  any  of  the  nitrates 
of  either  oxide  to  complete  decomposition,  when  the  acid  is  decomposed  and 
expelled,  oxidizing  the  metal  to  a  maximum,  if  it  happen  to  be  in  the  con- 
dition of  a  suboxide.  The  product  is  in  this  case  also  crystalline  and  very 
dense,  but  has  a  much  paler  colour  than  the  preceding ;  while  hot  it  is  nearly 
black.  It  is  by  this  method  that  the  oxide  is  generally  prepared ;  it  is  apt 
to  contain  undecomposed  nitrate,  which  may  be  discovered  by  strongly 
hoating  a  portion  in  a  test-tube :  if  red  fumes  are  produced  or  the  odour  of 
nitrous  acid  exhaled,  the  oxide  has  been  insufficiently  heated  in  the  process 
of  manufacture.  (3)  By  adding  caustic  potassa  in  excess  to  a  solution  of 
corrosive  sublimate,  by  which  a  bright  yellow  precipitate  of  oxide  is  thrown 
down,  which  only  differs  from  the  foregoing  preparations  in  being  destitute 
of  crystalline  texture  and  much  more  minutely  divided.''  It  must  be  well 
washed  and  dried. 

Red  oxide  of  mercury  is  slightly  soluble  in  water,  communicating  to  the 
latter  an  alkaline  reaction  and  metallic  taste  ;  it  is  highly  poisonous.  When 
strongly  heated,  it  is  decomposed,  as  before  observed,  into  metallic  mercury 
and  oxygen  gas. 

Nitrates  of  the  oxides  of  mercury.  —  Nitric  acid  varies  in  its  action 
upon  mercury,  according  to  the  temperature.  When  cold  and  somewhat 
diluted,  only  salts  of  the  grey  oxide  are  formed,  and  these  are  neutral  or 

*  By  referring  to  cyanogen,  it  will  be  perceived  that  when  the  equivalent  of  mercury  is 
considered  to  be  100,  the  constitution  of  the  cyanide  of  mercury  is  analogous  to  the  other 
metallic  cyanides,  but  when  taken  at  200,  it  becomes  a  bicyanide,  and  then  differs  from  all 
others. — R.  B. 

»  This  precipitate  is  considered  by  Shauffner  to  be  a  hydrate,  HgO,3nO,  for  by  exposure  to 
♦he  temperature  of  392°,  it  loses  water  amounting  to  over  20  per  cent,  of  its  weight.  —  R.  B. 


MERCURY,    OR    QUICKSILVER.  303 

basic  (t.  e.  with  excess  of  f;xidc),  as  the  acid  or  the  metal  happens  to  be  in 
excess.  When,  on  the  contrary,  the  nitric  acid  is  concentrated  and  hot,  the 
mercury  is  raised  to  its  highest  state  of  oxidation,  and  a  salt  of  the  red  oxide 
produced.  Both  classes  of  salts  are  apt  to  be  decomposed  by  a  large 
quantity  of  water,  giving  rise  to  insoluble,  or  sparingly  soluble,  compounds 
containing  an  excess  of  base. 

Neutral  nitrate  of  the  suboxide,  IIg20,N05-{-2HO,  forms  large  colourless 
crystals,  soluble  in  a  small  quantity  of  water  without  decomposition ;  it  is 
made  by  dissolving  mercury  in  an  excess  of  cold  dilute  nitric  acid. 

When  excess  of  mercury  has  been  employed,  a  finely  crystallized  basic 
salt  is,  after  some  time,  deposited,  containing  3Hg20,2N05-(-3HO;  this  is 
also  decomposed  by  water.  The  two  salts  are  easily  distinguished  when 
rubbed  in  a  mortar  with  a  little  chloride  of  sodium  ;  the  neutral  compound 
gives  nitrate  of  soda  and  calomel ;  the  basic  salt,  nitrate  of  soda  and  a  black 
compound  of  calomel  with  oxide  of  mercury.  A  black  substance,  called 
Hahnemann^ s  soluble  mercury,  is  produced  when  ammonia  in  small  quantity 
is  dropped  into  a  solution  of  the  nitrate  of  the  suboxide ;  it  contains  SHg^O, 
NOg-f-NHj,  or,  according  to  Sir  R.  Kane,  2HgO,N05-|-NH3;  the  composition 
of  this  preparation  evidently  varies  according  to  the  temperature  and  the 
concentration  of  the  solutions. 

Nitrates  of  the  Protoxide  {Red  Oxide)  of  Mercury.  —  By  dissolving  red  oxide 
of  mercury  in  excess  of  nitric  acid  and  evaporating  gently,  a  syrupy  liquid 
is  obtained,  which,  enclosed  in  a  bell-jar  over  lime  or  sulphuric  acid,  de- 
posits voluminous  crystals  and  crystalline  crusts.  The  crystals  and  crusts 
have  the  same  composition,  2(HgO,N05)-j-HO.  The  same  substance  is  de- 
posited from  the  syrupy  liquid  as  a  crystalline  powder  by  dropping  it  into 
concentrated  nitric  acid.  The  syrupy  liquid  itself  appears  to  be  a  definite 
compound  containing  HgOjNOg-f  2H0.  By  saturating  hot  dilute  nitric  acid 
with  the  red  oxide,  a  salt  is  obtained  on  cooling  which  crystallizes  in  needles, 
permanent  in  the  air,  containing  2 HgO,N05-f  HO.  ^^®  preceding  crystal- 
lized salts  are  decomposed  by  water,  with  production  of  compounds  more  and 
more  basic  as  the  washing  is  prolonged  or  the  temperature  of  the  water 
raised.    The  nitrates  of  the  protoxide  of  mercury  combine  with  ammonia. 

Sulphate  of  the  Suboxide  of  Mercury,  Hg20,S03,  falls  as  a  white  crystalline 
powder  when  sulphuric  acid  is  added  to  a  solution  of  the  nitrate  of  the  sub- 
oxide ;  it  is  but  slightly  soluble  in  water.  Sulphate  of  the  protoxide,  HgO, 
SO3,  is  readily  prepared  by  boiling  together  oil  of  vitriol  and  metallic  mer- 
cury until  the  latter  is  wholly  converted  into  a  heavy  white  crystalline  pow- 
der, which  is  the  salt  in  question ;  the  excess  of  acid  is  then  removed  by 
evaporation,  carried  to  perfect  dryness.  Equal  weights  of  acid  and  metal 
may  be  conveniently  employed.  Water  decomposes  the  sulphate,  dissolving 
out  an  acid  salt  and  leaving  an  insoluble,  yellow,  basic  compound,  formerly 
called  turpeth  or  turbith  mineral,  containing,  according  to  Kane's  analysis, 
3HgO,SOg.  Long-continued  washing  with  hot  water  entirely  removes  the 
remaining  acid,  and  leaving  pure  protoxide  of  mercury. 

SuBCHLORiDE  OF  MERCURY ;  CALOMEL ;  HgjCl.  —  This  vcry  importont  sub- 
{;tance  may  be  easily  and  well  prepared  by  pouring  a  solution  of  the  nitrate  of 
the  suboxide  into  a  large  excess  of  dilute  solution  of  common  salt.  It  falls 
as  a  dense  white  precipitate,  quite  insoluble  in  water  ;  it  must  be  thorouglily 
washed  with  boiling  distilled  water,  and  dried.  Calomel  is  generally  pro- 
cured by  another  and  more  complex  process.  Dry  sulphate  of  the  red  oxide 
is  rubbed  in  a  mortar  with  as  much  metallic  mercury  as  it  already  contains, 
and  a  quantity  of  common  salt,  until  the  globules  disappear,  and  an  uniform 
mixture  has  been  produced.  This  is  subjected  to  sublimation,  the  vapour  of 
the  calomel  being  carried  into  an  atmosphere  of  steam,  or  into  a  chamber 
COD  taining  air ;  it  is^  thus  condensed  in  a  minutely-divided  =tate,  and  the  la- 


S04  MERCURY,     OR    QUICKSILVER. 

borious  process  of  pwlverization  of  the  sublimed  mass  avoided.    The  reaction 
is  thus  explained:' — 

r  1  eq.  mercury^^ ^Calomel,  Hg^Cl. 

1  eq.  sulphate]   1  eq.  oxygen  ~~^ 

of  mercury    1    1  eq.  sul-       /  ^  -"""'^^ 

j^  phuric  acid.  ^ 

1  eq.  metallic  mercury 
1  eq.  common  \   1  eq.  chlorine 
salt  )   1  eq.  sodium     ^^  Sulphate  of  soda 

Pure  calomel  is  a  heavy,  white,  insoluble,  tasteless  powder;  it  rises  in 
vapour  at  a  \emperature  below  redness,  and  is  obtained  by  ordinary  subli- 
mation as  a  yellowish-white  crystalline  mass.  It  is  as  insoluble  in  cold  di- 
luted nitric  acid  as  the  chloride  of  silver  ;  boiling-hot  sti-ong  nitric  acid  oxi- 
dizes and  dissolves  it.  Calomel  is  instantly  decomposed  by  an  alkali,  or  by 
lime-water,  with  production  of  sub-oxide.  It  is  sometimes  apt  to  contain  a 
little  chloride,  which  would  be  a  very  dangerous  contamination  in  calomel 
employed  for  medical  purposes.  This  is  easily  discovered  by  boiling  with 
water,  filtering  the  liquid,  and  adding  caustic  potassa.  Any  corrosive  sub- 
limate is  indicated  by  a  yellow  precipitate. 

Protochloride  of  mercury  ;  corrosive  sublimate  ;  HgCl.  —  The  chlo- 
ride may  be  obtained  by  several  diflferent  processes.  (1)  When  metallic 
mercury  is  heated  in  chlorine  gas,  it  takes  fire  and  burns,  producing  this 
substance.  (2)  It  may  be  made  by  dissolving  the  red  oxide  in  hot  hydro- 
chloric acid,  when  crystals  of  corrosive  sublimate  separate  on  cooling.  (3) 
Or,  more  economically,  by  subliming  a  mixture  of  equal  parts  of  sulphate  of 
the  red  oxide  of  mercury  and  dry  common  salt ;  and  this  is  the  plan  gene- 
rally followed.     The  decomposition  is  thus  easily  explained :  ^  — 

f  1  eq.  mercury -^^  Corrosive  sublimate. 

1  eq.  sulphate  of  j  1  eq.  oxygen 
mercury 1  1  eq.  sul-     1 

[  phuric  acid  j 
-                            li.  f  1  eq.  chlorine  "^           '■■"^-^;:::i:v^ 
1  eq.  common  salt  |  ^  ^^  ^^^.^^   Il^S^lphate  of  soda. 

The  sublimed  protochloride  forms  a  white,  transparent,  crystalline  mass, 
of  great  density;  it  melts  at  509°  (265°C),  and  boils  and  volatilizes  at  a 
somewhat  higher  temperature.  It  is  soluble  in  16  parts  of  cold  and  3  of 
boiling  water,  and  crystallizes  from  a  hot  solution  in  long  white  prisms.  Al- 
cohol and  ether  also  dissolves  it  with  facility  ;  the  latter  even  withdraws  it 
from  a  watery  solution.    Chloride  of  mercury  combines  with  a  great  number 

«  If  the  grey  oxide  be  considered  as  protoxide,  the  sulphate  will  be  sulphate  of  the  binox- 
»de.  HgOa,  2S03,  and  the  decomposition  will  stand  thus : — 

1  1  v  +     C  1  eq.  mercury  — — ^  2  eq.  calomel,  IlgCl. 

1  eq.  sulphate   N  2  eq.  oxygen     ^^ 

of  mercury    ^  g  eq.  sulphuric  acjd 

1  eq.  metallic  mercury 

2  eq.  common    )   2  eq.  chlorine 
salt  \  2  eq.  sodium     -^  2  eq.  sulphate  of  soda. 

Or  on  the  other  supposition : — 

1  ea  sulDhate  of  f^  ''^-  "'^^^"^^ —^Bichloride  of  mercury. 

1  eq.  suipnate  oi  j  g  g,,  oxygen ^         _, — "^ 

"mercury ^2  4  sulphuric acid:^<^ 

<.  li  f  2  eq.  chlorine  '-     ^^"^^^^^5-^ 

2  ey.  common  salt  |  ^  ^  ^^^^^^ _:^**^2  eq.  sulphate  of  soda. 


MERCURY,     OR    QUICKSILVER.  305 

of  otlier  metallic  chlorides,  forming  a  series  of  beautiful  double  salts,  of 
•w^hich  the  ancient  sal  alemhroth  may  be  taken  as  a  good  example :  it  contains 
HgCl-f-NH^Cl-f-HO.  Corrosive  sublimate  absorbs  ammoniacal  gas  with  grea* 
avidity,  generating  a  compound  supposed  to  contain  2HgCl-f-NH,. 

When  excess  of  ammonia  is  added  to  a  solution  of  corrosive  sublimate,  p 
white  insoluble  substance  is  thrown  down,  long  known  under  the  name  of 
white  precipitate.  Sir  Robert  Kane,  who  has  devoted  much  attention  to  the 
salts  of  mercury,  represents  this  white  precipitate  as  a  double  amide  and 
chloride  of  mercury,  or  HgCl-j-HgNHj,  2  equivalents  of  chloride  of  mercury 
and  1  of  ammonia,  yielding  1  equivalent  of  the  new  body  and  1  of  hydro- 
chloric acid,  A  corresponding  black  compound,  HgjCl-f-HgNHj,  is  produced 
when  ammonia  is  digested  with  calomel,  which  must  be  carefully  distin- 
guished from  the  suboxide. 

Several  compounds  of  protochloride  of  mercury  with  protoxide  of  mercury 
also  exist.  These  are  produced  by  several  processes,  as  when  an  alkaline 
carbonate  or  bicarbonate  is  added  in  varying  proportions  to  a  solution  of 
corrosive  sublimate.  They  differ  greatly  in  colour  and  physical  character, 
and  are  mostly  decomposed  by  water. 

Corrosive  sublimate  forms  insoluble  compounds  with  many  of  the  azotized 
organic  principles,  as  albumin,  &c.  It  is  perhaps  to  this  property  that  its 
great  antiseptic  virtues  are  due.  Animal  and  vegetable  substances  are  pre- 
served by  it  from  decay,  as  in  Mr.  Kyan's  method  of  preserving  timber  and 
cordage.  Albumin  is  on  this  account  an  excellent  antidote  to  corrosive  sub- 
limate in  cases  of  poisoning. 

SuBiODiDE  OF  MERCURY,  HgjT.  —  The  subiodidc  is  formed  when  a  solution 
of  iodide  of  potassium  is  added  to  nitrate  of  the  suboxide  of  mercury ;  it 
separates  as  a  dirty  yellow,  insoluble  precipitate,  with  a  cast  of  green.  It 
may  be  prepared  by  rubbing  together  in  a  mortar  mercury  and  iodine  in  the 
proportion  of  2  equivalents  of  the  former  to  1  of  the  latter,  the  mixture  being 
moistened  from  time  to  time  with  a  little  alcohol. 

Protiodide  of  mercury,  Hgl.  —  When  solution  of  iodide  of  potassium  is 
mixed  with  protochloride  of  mercury,  a  precipitateTalls,  which  is  at  first 
yellow,  but  in  a  few  moments  changes  to  a  most  brilliant  scarlet,  which  colour 
is  retained  on  drying.  This  is  the  neutral  iodide ;  it  may  be  made,  although 
of  rather  duller  tint,  by  triturating  single  equivalents  of  iodine  and  mercury 
with  a  little  alcohol.  AVhen  prepared  by  precipitation,  it  is  better  to  weigh 
out  the  proper  proportions  of  the  two  salts,  as  the  iodide  is  soluble  in  an 
excess  of  either,  more  especially  in  excess  of  iodide  of  potassium.  The  iodide 
of  mercury  exhibits  a  very  remarkable  case  of  dimorphism,  attended  with 
differenc'e  of  colour,  the  latter  being  red  or  yellow,  according  to  the  figure 
assumed.  Thus,  when  the  iodide  is  suddenly  exposed  to  a  high  temperature, 
it  becomes  bright  yellow  throughout,  and  yields  a  copious  sublimate  of  minute 
but  brilliant  yellow  crystals.  If  in  this  state  it  be  touched  by  a  hard  body, 
it  instantly  becomes  red,  and  the  same  change  happens  spontaneously  after 
a  certain  lapse  of  time.  On  the  other  hand,  by  a  very  slow  and  careful  heat- 
ing, a  sublimate  of  red  crystals,  having  a  totally  different  form,  may  bo 
obtained,  which  are  permanent.  The  same  kind  of  change  happens  with  the 
freshly  precipitated  iodide,  as  Mr.  Warington  has  shown  the  yellow  crystals 
first  formed  breaking  up  in  the  course  of  a  few  seconds  from  the  passage  of 
the  salt  to  the  red  modification.* 

SuBsuLPHiDE  OF  MERCURY,  Hg^S.  —  The  black  precipitate  thrown  down 
from  a  solution  of  the  nitrate  of  suboxide  of  mercui-y  by  sulphuretted  hydro- 
gen, is  a  subsulphide ;  it  is  decomposed  by  heat  into  metallic  mercury  and 
neutral  sulphide. 

'  Memoirs  of  Chemical  Society  of  London,  i.  85. 
26* 


'806  MERCURY,     OR     QUICKSILVER. 

Sulphide  op  mercury  ;  artificial  cinnabar  ;  vermilion  ;  HgS.  —  Sul- 
phuretted hydrogen  gas  causes  a  precipitate  of  a  white  colour  when  passed 
in  small  quantity  into  a  solution  of  corrosive  sublimate  or  nitrate  of  the  red 
oxide ;  this  is  a  combination  of  sulphide  with  the  salt  itself.  An  excess  of 
the  gas  converts  the  whole  into  sulphide,  the  colour  at  the  same  time  chang- 
ing to  black.  When  this  black  sulphide  is  sublimed,  it  becomes  dark  red 
and  crystalline,  but  undergoes  no  change  of  composition ;  it  is  then  cinnabar. 
The  sulphide  is  most  easily  prepared  by  subliming  an  intimate  mixture  of  6 
parts  of  mercury  and  1  of  sulphur,  and  reducing  to  a  very  fine  powder  the 
resulting  cinnabar,  the  beauty  of  the  tint  depending  much  upon  the  extent 
to  which  division  is  carried.  The  red  or  crystalline  sulphide  may  also  be 
formed  directly,  without  sublimation,  by  heating  the  black  precipitated  sub- 
stance in  a  solution  of  pentasulphide  of  potassium ;  the  sulphide  of  mercury 
is  in  fact  soluble  to  a  certain  extent  in  the  alkaline  sulphides,  and  forms  with 
them  crystallizable  compounds. 

When  vermilion  is  heated  in  the  air,  it  yields  metallic  mercury  and  sul- 
phurous acid ;  it  resists  the  action  both  of  caustic  alkali  in  solution,  and  of 
strong  mineral  acids,  even  nitric,  and  is  only  attacked  by  aqua  regia. 


When  protoxide  of  mercury  is  put  into  a  large  excess  of  pure  caustic 
ammonia,  a  compound  is  obtained,  the  colour  of  which  varies  with  the  state 
of  the  oxide.  If  the  latter  be  amorphous,  it  is  pale  yellow ;  if  crystalline, 
then  the  action  of  the  ammonia  is  much  less  energetic,  and  the  product 
dai-ker  in  colour.  This  substance  possesses  very  extraordinary  properties, 
those,  namely,  of  a  most  powerful  base,  and  probably  belongs  to  the  same 
class  as  the  compound  bases  containing  platinum,  described  under  that 
metal.  The  body  in  question  bears  a  temperature  of  260°  (126° -SC),  with- 
out decomposition,  becoming  brown  and  anhydrous  by  the  loss  of  3  equiva- 
lents of  water.  In  this  state  it  contains  NH2Hg403=NH2Hg20-f-2HgO  or 
NHg40-|-2HO.  It  is  insoluble  in  watei',  alcohol,  and  ammonia;  cold  solu- 
tion of  potassa  has  no  action  on  the  hydrate,  but  at  a  boiling  heat  some 
ammonia  is  disengaged.  The  anhydrous  base  is  only  acted  on  by  hydrate 
of  potassa  in  fusion.  It  combines  directly  and  energetically  with  acids,  form- 
ing well-defined  compounds ;  it  absorbs  carbonic  acid  with  avidity  from  the 
air,  like  baryta  or  lime.  It  even  decomposes  ammoniacal  salts  by  boiling, 
expelling  the  ammonia  and  combining  with  the  acid.' 


The  salts  of  mercury  are  all  volatilized  or  decomposed  by  a  temperature 
of  ignition ;  those  which  fail  to  yield  the  metal  b3'  simple  heating  may  in  all 
cases  be  made  to  do  so  by  heating  in  a  test-tube  with  a  little  dry  carbonate 
of  soda.  The  metal  is  precipitated  from  its  soluble  combinations  by  a  plate 
of  copper,  and  also  by  a  solution  of  protochlox-ide  of  tin,  used  in  excess. 
The  behaviour  of  the  protochloride  and  soluble  salts  of  the  red  oxide  with 
»austic  potassa  and  ammonia  is  also  highly  characteristic. 


Alloys  of  mercury  with  other  metals  are  termed  amalgams  ;  mercury  dis- 
solves in  this  manner  many  of  the  metals,  as  gold,  silver,  tin,  lead,  &c. 
These  combinations  sometimes  take  place  with  considerable  violence,  as  in 
the  case  of  potassium,  where  light  and  heat  are  produced ;  besides  this,  many 
of  the  amalgams  crystallize  after  a  while,  becoming  solid.     The  amalgam  of 


Ann.  Chim.  et  Phys.  3d  series  xviii.  333. 


PLATINUM.  307 

tin  used  in  silvering  lookhig-glasses,  and  that  of  silver  sometimes  employed 
for  stopping  hollow  teeth,  are  examples. 

PLATINUM. 

Platinum,  palladium,  rhodium,  iridium,  ruthenium,  and  osmium,  form  a 
small  group  of  metals,  allied  in  some  cases  by  properties  in  common,  and 
still  more  closely  by  their  natural  association.  Crude  platinum,  a  native  alloy 
of  platinum,  palladium,  rhodium,  iridium,  and  a  little  iron,  occurs  in  grains 
and  rolled  masses,  sometimes  of  tolerably  large  dimensions,  mixed  with 
gravel  and  transported  materials,  on  the  slope  of  the  Ural  Mountains  in 
Russia,  in  Ceylon,  and  in  a  few  other  places.  It  has  never  been  seen  in  the 
rock,  which,  however,  is  judged,  from  the  accompanying  minerals,  to  have 
been  serpentine.  It  is  stated  to  be  always  present  in  small  quantities  with 
native  silver. 

From  this  substance  platinum  is  prepared  by  the  following  process  : — The 
crude  metal  is  acted  upon  as  far  as  possible  by  nitro-hydrochloric  acid,  con- 
taining an  excess  of  hydrochloric  acid,  and  slightly  diluted  with  water,  in 
order  to  dissolve  as  small  a  quantity  of  iridium  as  possible ;  to  the  deep  yel- 
lowish-red and  highly  acid  solution  thus  produced  sal-ammoniac  is  added,  by 
which  nearly  the  whole  of  the  platinum  is  thrown  down  in  the  state  of  am- 
monio-chloride.  This  substance  is  washed  with  a  little  cold  water,  dried 
and  heated  to  redness  ;  metallic  platinum  in  spongy  state  is  left.  Although 
this  metal  cannot  be  fused  into  a  compact  mass  by  any  furnace-heat,  yet  the 
same  object  may  be  accomplished  by  taking  advantage  of  its  property  of 
welding,  like  iron,  at  a  very  high  temperature.  The  spongy  platinum  is 
made  into  a  thin  uniform  paste  with  water,  introduced  into  a  slightly  conical 
mould  of  brass,  and  subjected  to  a  graduated  pressure,  by  which  the  water 
is  squeezed  out,  and  the  mass  rendered  at  length  sufficiently  solid  to  bear 
handling.  It  is  then  dried,  very  carefully  heated  to  whiteness,  and  ham- 
mered, or  subjected  to  powerful  pressure  by  suitable  means.  If  this  opera- 
tion has  been  properly  conducted,  the  platinum  will  now  be  in  a  state  to  bear 
forging  into  a  bar,  which  can  afterwards  be  rolled  into  plates,  or  drawn  into 
wire,  at  pleasure. 

Platinum  is  in  point  of  colour  a  little  whiter  than  iron ;  it  is  exceedingly 
malleable  and  ductile,  both  hot  and  cold,  and  is  very  infusible,  melting  only 
before  the  oxy-hydrogen  blowpipe.  It  is  the  (except  Iridium)  heaviest  sub- 
stance known,  its  specific  gravity  being  21-5.  Neither  air,  moisture,  nor  the 
ordinary  acids  attack  platinum  in  the  slightest  degree  at  any  temperature ; 
hence  its  high  value  in  the  coaistruction  of  chemical  vessels.  It  is  dissolved 
by  aqua  regia,  and  superficially  oxidized  by  fused  hydrate  of  potassa,  which 
enters  into  combination  with  the  oxide. 

The  remarkable  property  of  the  spongy  metal  to  determine  the  union  of 
oxygen  and  hydrogen  has  been  already  noticed.  There  is  a  still  more  curious 
state  in  which  platinum  can  be  obtained,  that  of  platinum-black,  where  the 
division  is  pushed  much  farther.  It  is  easily  prepared  by  boiling  a  solution 
of  bichloride  of  platinum  to  which  an  excess  of  carbonate  of  soda  and  a  quan- 
tity of  sugar  have  been  added,  until  the  precipitate  formed  after  a  little  time 
becomes  perfectly  black,  and  the  supernatant  liquid  colourless.  The  black 
powder  is  collected  on  a  filter,  washed,  and  dried  by  gentle  heat.  This  sub- 
stance appears  to  possess  the  property  of  condensing  gases,  more  especially 
oxygen,  into  its  pores  to  a  very  great  extent ;  when  placed  in  contact  with  a 
solution  of  formic  acid,  it  converts  the  latter,  with  copious  effervescence,  into 
carbonic  acid  ;  alcohol,  dropped  on  the  platinum-black,  becomes  changed  by 
oxidation  to  acetic  acid,  the  rise  of  temperature  being  often  sufficiently  great 
to  cause  inflammation.  When  exposed  to  a  red-heat,  the  black  substance 
shrinks  in  volume,  assumes  the  appearance  of  common  spongy  platinum,  and 


"S'^ 


PLATINUM. 


loses  these  peculiarities,  which  are  no  doubt  the  result  of  its  excessively  com- 
minuted state.  Platinum  forms  two  compounds  with  oxygen,  chlorine,  &c. 
The  equivalent  of  platinum  is  98-7/    Its  symbol  is  Pt. 

Protoxide  of  platinum,  PtO.  —  When  protochloride  of  platinum  is  di- 
gested with  caustic  potassa,  a  black  powder,  soluble  in  excess  of  alkali,  is  pro- 
duced :  this  is  the  protoxide.  It  is  soluble  in  acids  with  brown  colour,  and 
the  solutions  are  not  precipitated  by  sal-ammoniac.  When  binoxide  of  pla- 
tinum is  heated  with  solution  of  oxalic  acid,  it  is  reduced  to  protoxide,  which 
remains  dissolved.  The  liquid  has  a  dark  blue  colour,  and  deposits  fine  cop- 
per-red needles  of  oxalate  of  the  protoxide  of  platinum. 

Binoxide  op  platinum,  PtOj.  —  This  is  best  prepared  by  adding  nitrate 
of  baryta  to  sulphate  of  the  binoxide  of  platinum ;  sulphate  of  baryta  and 
nitrate  of  the  binoxide  are  produced.  From  the  latter,  caustic  soda  precipi- 
tates one-half  of  the  binoxide  of  platinum.  The  sulphate  is  itself  obtained 
by  acting  with  strong  nitric  acid  upon  the  bisulphide  of  platinum,  which  falls 
as  a  black  powder  when  a  solution  of  bichloride  is  dropped  into  sulphide  of 
potassium.  The  hydrate  of  the  binoxide  is  a  bulky  brown  powder,  which, 
when  gently  heated,  becomes  black  and  anhydrous.  It  may  also  be  formed 
by  boiling  bichloride  of  platinum  with  a  great  excess  of  caustic  soda,  and 
then  adding  acetic  acid.  It  dissolves  in  acids,  and  also  combines  with  bases ; 
the  salts  have  a  yellow  or  red  tint,  and  a  great  disposition  to  unite  with  salts 
of  the  alkalis  and  alkaline  earths,  giving  rise  to  a  series  of  double  compounds, 
which  are  not  precipitated  by  excess  of  alkali.  A  combination  of  binoxide 
of  platinum  with  ammonia  exists,  which  is  explosive.  Both  oxides  of  plati- 
num are  reduced  to  the  metallic  state  by  ignition. 

Protochloride  of  platinum,  PtCl. — The  protochloride  is  produced  when 
bichloride  of  platinum,  dried  and  powdered,  is  exposed  for  some  time  to  a 
heat  of  400°  (204°  -SC),  by  which  half  of  the  chlorine  is  expelled ;  also,  when 
sulphurous  acid  is  passed  into  a  solution  of  the  bichloride  until  the  latter 
ceases  to  give  a  precipitate  with  sal-ammoniac.  It  is  a  greenish-grey  pow- 
der, insoluble  in  water,  but  dissolved  by  hydrochloric  acid.  The  latter  solu- 
tion, mixed  with  sal-ammoniac  or  chloride  of  potassium,  deposits  a  double 
salt  in  fine  red  prismatic  crystals,  containing  in  the  last  case,  PtCl-f-KCl. 
The  corresponding  sodium-compound  is  very  soluble  and  difficult  to  crystal- 
lize. The  protochloride  is  decomposed  by  heat  into  chlorine  and  metallic 
platinum. 

Bichloride  or  perchlobidb  of  Platinum,  PtCl,. — This  substance  is  al- 
ways formed  when  platinum  is  dissolved  in  nitro-hydrochloric  acid.  The 
acid  solution  yields  on  evaporation  to  dryness*  a  red  or  brown  residue,  deli- 
quescent, and  very  soluble  both  in  water  and  alcohol ;  the  aqueous  solution 
has  a  pure  orange-yellow  tint.  Bichloride  of  platinum  combines  to  double 
salts  with  a  great  variety  of  metallic  chlorides ;  the  most  important  of  these 
compounds  are  those  containing  the  metals  of  the  alkalis  and  ammonium. 
Bichloride  of  platinum  and  chloride  of  potassium,  VtQ\^,  KCl,  forms  a  bright  yel- 
low crystalline  precipitate,  being  produced  whenever  solutions  of  the  chlo- 
rides of  platinum  and  of  potassium  are  mixed,  or  a  salt  of  potassa,  mixed 
with  a  little  hydrochloric  acid,  added  to  bichloride  of  platinum.  It  is  feebly 
soluble  in  water,  still  less  soluble  in  dilute  alcohol,  and  is  decomposed  with 
some  difficulty  by  heat.  It  is  readily  reduced  by  hydrogen  at  a  high  tem- 
perature, furnishing  a  mixture  of  chloride  of  potassium  and  platinum-black  ; 
the  latter  substance  may  thus,  indeed,  be  very  easily  prepared.  The  sodium- 
salt,  PtClj,  NaCl-f-6H0,  is  very  soluble,  crystallizing  in  large,  transparent, 
yellow-red  prisms  of  great  beauty.  The  ammonio-chloride  of  platinum,  PtClg, 
NH^Cl,  is  indistinguishable,  in  physical  characters,  from  the  potassium-salt; 

»  98-94,  Prof.  Andi-ews,  Chem.  Gar.,  Oct.  1852. 


PLATINUM.  dVU 

it  is  thrown  down  as  a  precipitate  of  small,  transparent,  yellow,  octuhedral 
crystals  when  feal-amraoniac  is  mixed  with  chloride  of  platinum ;  it  is  but 
feebly  soluble  in  water,  still  less  so  in  dilute  alcohol,  and  is  decomposed  by 
heat,  yielding  spongy  platinum,  while  sal-ammoniac,  hydrochloric  acid,  and 
nitrogen  are  driven  off.  Compounds  of  platinum  with  iodine,  bromine,  sul- 
phur, and  phosphorus  have  been  formed,  but  are  comparatively  unim- 
portant. 

Some  very  extraordinary  compounds  have  been  derived  from  the  proto- 
chloride  of  platinum. 

When  ammonia  in  excess  is  added  to  a  hot  solution  of  the  protochloride 
of  platinum  and  ammonium,  a  green  crystalline  salt  separates  after  a  time, 
which  is  quite  insoluble  in  water,  and  is  not  affected  by  hydrochloric  or  sul- 
phuric acids,  ammonia,  or  even  a  boiling-hot  solution  of  potassa.  This  sub- 
stance is  known  as  the  green  salt  of  Magnus,  and  contains  the  elements  of 
protochloride  of  platinum  and  ammonia,  or  PtCl+NHg. 

When  the  above  compound  is  heated  with  concentrated  nitric  acid,  it  be- 
comes converted  into  a  white,  granular,  crystalline  powder,  which  on  addition 
of  water  dissolves,  leaving  a  residue  of  metallic  platinum.  The  solution 
yields  on  standing  small,  brilliant,  colourless  prisms  of  a  substance  very  so- 
luble in  water,  containing  the  elements  of  protochloride  of  platinum,  ammo- 
nia, nitric  acid,  and  an  additional  equivalent  of  oxygen : — 

PtCl,N2HaO+N06. 

The  platinum  and  chlorine  in  this  curious  body  are  insensible  to  ordinary 
reagents,  and  ammonia  is  evolved  from  it  only  on  boiling  with  caustic  alkali ; 
the  presence  of  nitric  acid  can  be  detected  immediately  by  gently  heating  a 
small  portion  with  copper-filings  and  oil  of  vitriol.  Prom  this  substance  a 
series  of  salt-like  bodies  can  be  obtained,  some  of  which  have  been  carefully 
studied  by  M.  Gros.  Thus,  when  treated  with  hydrochloric  acid,  the  nitrio 
acid  is  wholly  displaced,  and  a  compound  formed  which  crystallizes  in  small, 
transparent,  yellowish  octahedrons,  sparingly  soluble  in  boiling  water,  con- 
taining PtCljNj^e^^*  With  sulphuric  acid  it  gives  a  substance  which  crys- 
tallizes in  small,  sparingly  soluble,  colourless  needles,  containing  PtCl, 
NjHgO-f-SOg.  The  oxalic  acid  compound  is  white  and  insoluble ;  it  contains 
PtCl,N2HgO-f-C203.  Crystallizabie  compounds  containing  phosphoric,  tar- 
taric, citric,  malic,  formic,  and  even  carbonic  acids,  were  obtained  by  similar 
means.  These  substances  have  very  much  the  characters  of  salts  of  a  com- 
pound base  or  gwase-metal  containing  PtCl,N2Hg,  and  which  yet  remains  un- 
known in  a  separate  state.  M.  Raewsky  has  repeated  and  extended  the 
observations  of  M.  Gros. 

MM.  Reiset  and  Peyrone  have  also  described  two  other  basic  bodies  con- 
taining platinum  in  the  same  remarkable  condition :  these  differ  from  the 
preceding  in  being  free  from  chlorine. 

Protochloride  of  platinum  put  into  ammonia  becomes  rapidly  converted 
into  a  green  powder,  which,  by  boiling,  slowly  dissolves ;  the  solution,  on 
evaporation  and  cooling,  furnishes  beautiful  yellowish  crystals  of  the  chlorine- 
compound  of  one  of  these  bases,  compounded  of  platinum  and  the  elements 
of  ammonia.  The  crystals  contained  PtNgHgCl-f-HO.  The  equivalent  of 
water  is  easily  expelled  by  heat,  and  regained  by  absorption  from  the  air. 
The  green  salt  of  Magnus,  boiled  with  ammonia,  yields  the  same  product. 

A  solution  of  this  substance,  mixed  with  nitrate  of  silver,  gives  chloride 
of  silver  and  the  nitrate  of  the  new  base,  which  crystallizes  on  evaporation 
in  fine,  white,  transparent  needles,  containing  PtNjHgO-j-NOj.  The  sulphide, 
iodide,  and  bromide  are  also  crystallizabie.  Two  carbonates  exist.  By  adding 
baryta-water  to  a  solution  of  the  sulphate,  or  by  treating  the  chloride  with 
protoxide  of  silver,  and  evaporating  the  filtered  liquid  in  vactco,  a  white, 


310  PLATINUM. 

crystalline,  deliquescent  mass  is  obtained,  which  is  the  hydrate  of  the  base, 
PtNgHgO-f-HO.  It  is  almost  comparable  in  point  of  alkalinity  with  potassa 
itself,  absorbing  carbonic  acid  with  energy,  and  decomposing  ammoniacal 
salts.  When  this  hydrate  is  heated  to  230°  (110°C),  it  abandons  water  and 
ammonia,  and  leaves  a  greyish,  porous,  insoluble  mass  containing  PtNHjjO. 
This  is  probably  an  isomeric  modification  of  the  second  base,  whose  salts  are 
mentioned  below. 

When  a  solution  of  the  iodide,  PtNgHgl,  is  long  boiled,  it  deposits  a  spar- 
ingly soluble  yellow  powder,  the  composition  of  which  is  expressed  by  the 
formula  PtNHjI :  this  is  the  iodine-compound  of  a  second  basic  substance, 
PtNHg ;  and  from  it  by  double  decomposition  a  series  of  analogous  salts  can 
be  obtained.  When  the  iodine-compound  is  treated  with  protoxide  of  silver, 
the  base  itself  is  obtained  in  the  form  of  a  powerfully  alkaline  solution.  The 
green  salt  of  Magnus  has  the  same  composition  as  the  chloride  of  this- new 
base,  which  is  yellow  and  soluble  in  boiling  water,  and  may  be  converted  into 
it.  The  salts  of  the  first  base  are  generally  convertible  into  those  of  the 
second  by  heat,  and  the  converse  change  may  also  be  often  efiected  by  ebul- 
lition with  ammonia. 

The  subject  of  the  platinum-bases  appears  to  be  by  no  means  exhausted. 
Only'quite  recently  another  remarkable  basic  compound  containing  ammonia 
and  platinum  has  been  discovered  by  M.  Gerhardt.  The  chloride  of  Reiset's 
second  base,  the  compound  PtNHgCl,  when  treated  with  chlorine,  absorbs 
this  element,  and  becomes  converted  into  a  lemon-yellow  powder,  consisting 
of  small  octahedrons,  and  having  the  composition  PtNHgClg.  Boiled  with 
nitrate  of  silver,  this  substance  yields  chloride  of  silver  and,  according  to  the 
quantity  of  nitric  acid  present,  a  salt,  PtNH302,2N05,  or  PtNHgOjiNOg-j- 
8H0.  On  adding  ammonia  to  the  latter  nitrate,  a  crystalline  precipitate 
takes  place,  which  consists  of  PtNH302-|-2HO.  This  substance,  which  is 
slightly  soluble  in  water,  may  be  viewed  as  the  hydrated  base  existing  in  the 
bichloride  and  in  the  nitrates  previously  described. 


The  bichloride,  or  a  solution  of  binoxide  of  platinum,  can  be  at  once  re- 
cognized by  the  yellow  precipitate  with  sal-ammoniac,  decomposable  by  heat, 
itith  production  of  spongy  metal. 


Bichloride  of  platinum  and  the  sodio-chloride  of  platinum  are  employed 
in  analytical  investigations  to  detect  tlie  presence  of  potassa,  and  separate  it 
from  soda.  For  the  latter  purpose,  the  alkaline  salts  are  converted  into 
chlorides,  and  in  this  condition  mixed  with  four  times  their  weight  of  sodio- 
chloride  of  platinum  in  crystals,  the  whole  being  dissolved  in  a  little  water^ 
When  the  formation  of  the  yellow  salt  appears  complete,  alcohol  is  added, 
and  the  precipitate  collected  on  a  weighed  filter,  washed  with  weak  spirit, 
carefully  dried,  and  weighed.  The  chloride  of  potassium  is  then  easily  reck- 
oned from  the  weight  of  the  double  salt,  and  this,  subtracted  from  the  weight 
of  the  mixed  chlorides  employed,  gives  that  of  the  chloride  of  sodium  by 
difference;  100  parts  of  potasso-chloride  of  platinum  correspond  to  35  06 
parts  of  chloride  of  potassium. 

Capsules  and  crucibles  of  platinum  are  of  great  value  to  the  chemist;  the 
latter  are  constantly  used  in  mineral  analysis  for  fusing  siliceous  matter  with 
alkaline  carbonates.  They  suffer  no  injury  in  this  operation,  although  the 
caustic  alkali  roughens  and  corrodes  the  metal.  The  experimenter  must  be 
particularly  careful  to  avoid  introducing  any  oxide  of  any  easily  fusible 
metal,  as  that  of  lead  or  tin,  into  a  platinum  crucible.  If  reduction  should 
by  any  means  occui,  these  metals  will  at  once  alloy  themselves  with  the  pla- 


PALLADIUM.  311 

tinura,  and  the  vessel  will  be  destroyed.  A  platinum  crucible  must  never  be 
put  naked  into  the  fire,  but  be  always  placed  within  a  covered  earthen 
crucible. 

PALLADIUM. 

The  solution  of  crude  platinum,  from  which  the  greater  part  of  that  metal 
has  been  precipitated  by  sal-ammoniac,  is  neutralized  by  carbonate  of  soda, 
and  mixed  with  a  solution  of  cyanide  of  mercury ;  cyanide  of  palladium 
separates  as  a  whitish  insoluble  substance,  which,  on  being  washed,  di'ied, 
and  heated  to  redness,  yields  metallic  palladium  in  a  spongy  state.  The  pal- 
ladium is  then  welded  into  a  mass,  in  the  same  manner  as  platinum. 

Palladium  closely  corresponds  with  platinum  in  colour,  appearance,  and 
difl&cult  fusibility ;  it  is  also  very  malleable  and  ductile.  In  density  it  differs 
very  much  from  that  metal,  being  only  11-8.  Palladium  is  more  oxidable 
than  platinum.  When  heated  to  redness  in  the  air,  especially  in  the  state 
of  sponge,  it  acquires  a  blue  or  purple  superficial  film  of  oxide,  which  is 
again  reduced  at  a  white  heat.  This  metal  is  slowly  attacked  by  nitric  acid ; 
its  best  solvent  is  aqua  regia.  There  are  two  compounds  of  palladium  and 
oxygen. 

The  equivalent  of  palladium  is  53-3 ;  its  symbol  is  Pd. 

Protoxide  qf  palladium,  PdO.  —  This  is  obtained  by  evaporating  to  dry- 
ness, and  cautiously  heating,  the  solution  of  palladium  in  nitric  acid.  It  is 
black,  and  but  little  soluble  in  acids.  The  hydrate  falls  as  a  dark  brown 
precipitate  when  carbonate  of  soda  is  added  to  the  above  solution.  It  is 
decomposed  by  a  strong  heat. 

Binoxide  of  palladium,  PdOjj.  —  The  pure  binoxide  is  very  difficult  to 
obtain.  When  solution  of  caustic  potassa  is  poured,  little  by  little,  with 
constant  stirring,  upon  the  double  chloride  of  palladium  and  potassium  in  a 
dry  state,  the  latter  is  converted  into  a  yellowish -brown  substance,  wMch  is 
the  binoxide,  in  combination  with  water  and  a  little  alkali.  It  is  but  feebly 
soluble  in  acids. 

Pkotochloride  of  palladium,  PdCl.  —  The  solution  of  the  metal  in  aqua 
regia  yields  this  substance  when  evaporated  to  drynesss.  It  is  a  dark  brown 
mass,  soluble  in  water  when  the  heat  has  not  been  too  great,  and  forms 
double  salts  with  many  metallic  chlorides.  The  potassio-  and  ammonio- 
chlorides  of  palladium  are  much  more  soluble  than  those  of  platinum ;  they 
have  a  brownish-yellow  tint. 

Bichloride  of  palladium  only  exists  in  solution,  and  in  combination  with 
the  alkaline  chlorides.  It  is  formed  when  the  protochloride  of  palladium  is 
digested  in  aqua  regia.  The  solution  has  an  intense  brown  colour,  and  is 
decomposed  by  evaporation.  Mixed  with  chloride  of  potassium  or  sal-ammo- 
niac, it  gives  rise  to  a  red  crystalline  precipitate  of  double  salt  which  is  but 
little  soluble  in  water. 

A  sulphide  of  palladium,  PdS,  is  formed  by  fusing  the  metal  with  sulphur, 
or  by  precipitating  a  solution  of  protochloride  by  sulphuretted  hydrogen. 


A  palladium-salt  is  well  marked  by  the  pale  yellowish-white  precipitate 
with  solution  of  cyanide  of  mercury,  convertible  by  heat  into  the  spongy 
metal.    This  precipitate  is  a  double  salt,  having  the  formula  PdCy,HgCy,HO. 


Palladium  is  readily  alloyed  with  other  metals,  as  copper :  one  of  these 
compounds,  namely,  the  alloy  with  silver,  has  been  applied  to  useful  pur- 
poses. A  native  alloy  of  gold  with  palladium  is  found  in  the  Brazils,  and 
imported  into  England. 


312  RHODIUM  —  IRIDIUM. 


EHODIUM. 


The  solution  from  "wliich  platinum  and  palladium  have  been  separated  in 
the  manner  described  is  mixed  with  hydrochloric  acid,  and  evaporated  to 
dryness.  The  residue  is  treated  with  alcohol  of  specific  gravity  0-837, 
which  dissolves  everything  except  the  double  chloride  of  rhodium  and  sodium. 
This  is  well  washed  with  spirit,  dried,  heated  to  whiteness,  and  then  boiled 
with  water ;  chloride  of  sodium  is  dissolved  out,  and  metallic  rhodium  re- 
mains. Thus  obtained,  rhodium  is  a  white,  coherent,  spongy  mass,  which 
is  more  infusible  and  less  capable  of  being  welded  than  platinum.  Its  spe- 
cific gravity  varies  from  10-6  to  11. 

Rhodium  is  very  brittle:  reduced  to  powder  and  heated  in  the  air,  it  be- 
comes oxidized,  and  the  same  alteration  happens  to  a  greater  extent  when  it 
is  fused  with  nitrate  or  bisulphate  of  potassa.  None  of  the  acids,  singly  or 
conjoined,  dissolve  this  metal,  unless  it  be  in  the  state  of  allo}^,  as  with  pla- 
tinum, in  which  it  is  attacked  by  aqua  regia. 

The  equivalent  of  rhodium  is  52-2 ;  its  symbol  is  R. 

Protoxide  of  rhodium,  RO,  is  obtained  by  roasting  finely  divided  me- 
tallic rhodium.     It  is  but  little  known. 

Sesquioxide  of  rhodium,  R3O3.  —  Finely-powdered  metallic  rhodium  is 
heated  in  a  silver  crucible  with  a  mixture  of  hydrate  of  potassa  and  nitre ; 
the  fused  mass  boiled  with  water  leaves  a  dark  brown,  insoluble  substance, 
consisting  of  sesquioxide  of  rhodium  in  union  with  potassa.  This  is  digested 
with  hydrochloric  acid,  which  removes  the  potassa  and  leaves  a  greenish- 
grey  hydrate  of  the  sesquioxide  of  rhodium,  insoluble  in  acids.  A  soluble 
modification  of  the  same  substance,  retaining,  however,  a  portion  of  alkali, 
may  be  had  by  adding  an  excess  of  carbonate  of  potassa  to  the  double  chlo- 
ride of  rhodium  and  potassium,  and  evaporating. 

Sesquichloride  of  rhodium,  RgClg. — The  pure  sesquichloride  is  prepared 
by  adding  hydrofluosilicic  acid  to  the  double  chloride  of  rhodium  and  potas- 
sium, evaporating  the  filtered  solution  to  dryness,  and  dissolving  the  residue 
in  water.  It  forms  a  brownish-red  deliquescent  mass,  soluble  in  water,  with 
a  fine  red  colour.  It  is  decomposed  by  heat  into  chlorine  and  metallic  rho- 
dium. The  chloride  of  rhodium  and  potassium,  R2Cl3-j-2KCl-}-2HO,  is  pre- 
pared by  heating  in  a  stream  of  chlorine  a  mixture  of  equal  parts  finely 
powdered  rhodium  and  chloride  of  potassium.  This  salt  has  a  fine  red 
colour,  is  soluble  in  water,  and  crystallizes  in  four-sided  prisms.  Chloride  of 
rhodium  and  sodium  is  also  a  very  beautiful  red  salt,  obtained  by  a  similar 
process;  it  contains  RgCla-f^NaCl-f-lSHO.  The  chloride  of  rhodium  and 
ammonium  resembles  the  potassium-compound. 

Sulphate  of  rhodium,  RjOgjSSOj.  —  The  sulphide  of  rhodium,  obtained 
by  precipitating  one  of  the  salts  by  a  soluble  sulphide,  is  oxidized  by  strong 
nitric  acid.  The  product  is  a  browapowder,  nearly  insoluble  in  nitric  acid, 
but  dissolved  by  water ;  it  cannot  be  made  to  crystallize.  Sulphate  of  rho- 
dium and  potassium,  is  produced  when  metallic  rhodium  is  strongly  heated 
with  bisulphate  of  potassa.     It  is  a  yellow  salt,  slowly  soluble  in  cold  water. 

An  alloy  of  steel  with  a  small  quantity  of  rhodium  is  said  to  possess  ex- 
tremely valuable  properties. 

IRIDIUM. 

When  crude  platinum  is  dissolved  in  aqua  regia,  a  small  quantity  of  a  grey 
scaly  metallic  substance  usually  remains  behind,  having  altogether  resisted 
the  action  of  the  acid ;  this  is  a  native  alloy  of  iridium  and  osmium.  It  is 
reduced  to  powder,  mixed  with  an  equal  weight  of  dry  chloride  of  sodium, 
and  heated  to  redness  in  a  glass  tube,  through  which  a  stream  of  moist  chlo- 


IRIDIUM.  813 

rine  gas  is  transmitted.  The  farther  extremity  of  the  tube  is  connected  with 
a  receiver  containing  solution  of  ammonia.  The  gas,  under  these  circum- 
stances, is  rapidly  absorbed,  chloride  of  iridium  and  chloride  of  osmium  be- 
ing produced :  the  former  remains  in  combination  with  the  chloride  of  so- 
dium; the  latter,  being  a  volatile  substance,  is  carried  forward  into  the 
receiver,  where  it  is  decomposed  by  the  water  into  osmic  and  hydrochloric 
acids,  which  combine  with  the  alkali.  The  contents  of  the  tube  when  cold 
are  treated  with -water,  by  which  the  double  chloride  of  iridium  and  sodium 
is  dissolved  out ;  this  is  mixed  with  an  excess  of  carbonate  of  soda,  and 
evaporated  to  dryness.  The  residue  is  ignited  in  a  crjicible,  boiled  with 
water,  and  dried ;  it  then  consists  of  a  mixture  of  sesquioxide  of  iron,  and 
a  combination  of  oxide  of  iridium  with  soda ;  it  is  reduced  by  hydrogen  at 
a  high  temperature,  and  treated  successively  with  water  and  strong  hydro- 
chloric acid,  by  which  the  alkali  and  the  iron  are  removed,  while  metallic 
iridium  is  left  in  a  divided  state.  By  strong  pressure  and  exposure  to  a 
white  heat,  a  certain  degree  of  compactness  may  be  communicated  to  the 
metal. 

Iridium  is  a  white  brittle  metal,  fusible  with  great  diflBculty  before  the 
oxy-hydrogen  blowpipe.*  It  is  not  attacked  by  any  acid,  but  is  oxidized  by 
fusion  with  nitre,  and  by  ignition  to  redness  in  the  air. 

The  equivalent  of  iridium  is  99.     Its  symbol  is  Ir. 

Oxides  of  iridium. — Four  of  these  compounds  are  described.  Proioxidt 
of  iridium,  IrO,  is  prepared  by  adding  caustic  alkali  to  the  protochloride, 
and  digesting  the  precipitate  in  an  acid.  It  is  a  heavy  black  powder,  inso- 
luble in  acids.  It  may  be  had  in  the  state  of  hydrate  by  precipitating  the 
protochloride  of  iridium  and  sodium  by  caustic  potassa.  The  hydrate  is  so- 
luble in  acids  with  dirty  green  colour.  Sesquioxide,  Ir^Oj,  is  produced  when 
iridium  is  heated  in  the  air,  or  with  nitre  ;  it  is  best  prepared  by  fusing  in 
a  silver  crucible  a  mixture  of  carbonate  of  potassa  and  the  terchloride  of 
iridium  and  potassium,  and  boiling  the  product  witli  water.  This  oxide  is 
bluish-black,  and  is  quite  insoluble  in  acids.  It  is  reduced  by  combustible 
substances  with  explosion.  Binoxide  of  iridium,  IrO^,  is  unknown  in  a  sepa- 
rate state ;  it  is  supposed  to  exist  in  the  sulphate,  produced  when  the  sul- 
phide is  oxidized  by  nitric  acid.  A  solution  of  sulphate  heated  with  excess 
cf  alkali  evolves  oxygen  gas,  and  deposits  sesquioxide  of  iridium.  Teroxide 
of  iridium,  IrOj,  is  produced  when  carbonate  of  potassa  is  gently  heated  with 
the  terchloride  of  iridium ;  it  forms  a  greyish-yellow  hydrate,  which  con- 
tains alkali. 

Chlorides  of  iridium.  — Protochloride,  IrCl,  is  formed  when  the  metal  is 
brought  in  contact  with  chlorine  at  a  dull  red-heat;  it  is  a  dark  olive-green 
insoluble  powder.  ^  It  is  dissolved  by  hydrochloric  acid,  and  forms  double 
salts  with  the  alkaline  chlorides,  which  have  a  green  colour.  The  sesquichlo- 
ride,  IrjClg,  is  prepared  by  strongly  heating  iridium  with  nitre,  adding  water, 
and  enough  nitric  acid  to  saturate  the  alkali,  warming  the  mixture,  and  then 
dissolving  the  precipitated  hydrate  of  the  sesquioxide  in  hydrochloric  acid. 
It  forms  a  dark  yellowish-brown  solution.  This  substance  combines  with 
metallic  chlorides.  Bichloride  of  iridium  is  obtained  in  solution  by  adding 
hydrofluosilicic  acid  to  the  bichloride  of  iridium  and  potassium,  formed 
when  chlorine  is  passed  over  a  heated  mixture  of  iridium  and  chloride 
of  potassium.  It  forms  vrith  metallic  chlorides  a  number  of  double  salts, 
which  resemble  the  platinum-compounds  of  the  same  order.  Terchloride  c^ 
iridium,  IrClg,  is  unknown  in  a  separate  state.  Terchloride  of  iridium  ana 
potassium  is  obtained  by  heating  iridium  with  nitre,  and  then  dissolving  the 

«  It  is  the  heaviest  substance  known,  its  specific  gravity,  according  to  Trofcssor  Hare,  belnic 
21-9.    Proceedings  of  the  Amer.  Phih  Soc.  May  and  June,  1842. —R,  B 
27 


314  RUTHENIUM  —  OSMIUM. 

whole  In  aqua  regia,  and  evaporating  to  dryness.  The  excess  of  chloride  of 
potassium  may  be  extracted  by  a  small  quantity  of  water.  The  crystallized 
salt  has  a  beautiful  red  colour.  The  variety  of  tints  exhibited  by  the  diffe- 
rent soluble  compounds  af  iridium  is  very  remarkable,  and  suggested  the 
name  of  the  metal,  from  the  word  iris. 

Platinum,  palladium,  and  iridium  combine  with  carbon  when  heated  in  the 
flame  of  a  spirit-lamp ;  they  acquire  a  covering  of  soot,  which,  when  burned, 
leaves  a  kind  of  skeleton  of  spongy  metal. 

,  BUTHENIUM. 

M.  Claus  has  described  under  this  name  a  new  metal  contained  in  the 
residue  from  crude  platinum,  insoluble  in  aqua  regia.  It  closely  resembles 
iridium  in  its  general  characters,  but  yet  possesses  distinctive  features  of 
its  own.  It  was  obtained  in  the  form  of  small  angular  masses,  with  perfect 
metallic  lustre,  very  brittle  and  infusible.  Its  specific  gravity  is  8-6.  It 
resists  the  action  of  acids,  but  oxidizes  readily  when  heated  in  the  air. 

The  equivalent  of  ruthenium  is  52-2,  and  its  symbol  Ru. 

Oxides  of  ruthenium.  —  Protoxide  of  ruthenium,  RuO,  is  a  greyish-black 
metallic-looking  powder,  obtained  by  heating  bichloride  of  ruthenium  with 
excess  of  carbonate  of  soda  in  a  stream  of  carbonic  acid  gas,  and  then  wash- 
ing away  the  soluble  saline  matter.  It  is  insoluble  in  acids.  The  sesquioxide, 
RugOg,  in  the  anhydrous  condition  is  a  bluish-black  powder  formed  by  heating 
the  metal  in  the  air.  It  is  also  precipitated  by  alkalis  from  the  sesquichlo- 
ride  as  a  blackish-brown  hydrate,  soluble  in  acids  with  orange-yellow  colour. 
The  binoxide,  RuO,,  is  a  deep  blue  powder,  procured  by  roasting  the  bisul- 
phide. A  hydrate  of  this  oxide  is  known  in  an  impure  condition.  An  acid 
of  ruthenium  is  also  supposed  to  exist. 

Sesquichloride  of  ruthenium,  RujClg,  is  an  orange-yellow  soluble  salt  of 
astringent  taste ;  when  the  solution  is  heated,  it  becomes  green  and  finally 
blue,  by  reduction,  in  all  probability,  to  protochloride.  Sesquichloride  of 
ruthenium  forms  double  salts  with  the  chlorides  of  potassium  and  ammonium. 


The  solution  of  osmic  acid  in  ammonia,  already  mentioned,  is  gently  heated 
for  some  time  in  a  loosely-stopped  vessel ;  its  original  yellow  colour  becomes 
darker,  and  at  length  a  brown  precipitate  falls,  which  is  a  combination  of 
sesquioxide  of  osmium  with  ammonia :  it  results  from  the  reduction  of  the 
osmic  acid  by  the  hydrogen  of  the  volatile  alkali.  A  little  of  the  precipitate 
is  held  in  solution  by  the  sal-ammoniac,  but  may  be  recovered  by  heating 
the  clear  liquid  with  caustic  potassa.  The  brown  substance  is  dissolved  in 
hydrochloric  acid,  a  little  chloride  of  ammonium  added,  and  the  whole  evapo- 
rated to  dryness.  The  residue  is  strongly  heated  in  a  small  porcelain  retort ; 
the  oxygen  of  the  oxide  combines  with  hydrogen  from  the  ammonia,  vapour 
of  water,  hydrochloric  acid,  and  sal-ammoniac  are  expelled,  and  osmium  left 
behind,  as  a  greyish  porous  mass,  having  the  metallic  lustre. 

In  the  most  compact  state  in  which  this  metal  can  be  obtained,  it  has  a 

luish-white  colour,  and,  although  somewhat  flexible  in  thin  plates,  is  yet 

asily  reduced  to  powder.     Its  specific  gravity  is  10;  it  is  neither  fusible 

nor  volatile.     It  burns  when  heated  to  redness,  yielding  osmic  acid,  which 

volatilizes.     Osmate  of  potassa  is  produced  when  the  metal  is  fused  with 

nitre.     When  in  a  finely  divided  state,  it  is  oxidized  by  strong  nitric  acid. 

The  equivalent  of  osmium  is  99-6 ;  its  symbol  is  Os. 

Oxides  op  osmium. — Five  compounds  of  osmium  with  oxygen  are  known. 

Protoxide,  OsO,  is  obtained,  in  combination  with  a  little  alkali,  vhcn  caustic 

potassa  is  added  to  a  solution  of  protochloride  of  osmium  and  potassium.    It 

is  a  dark  green  powder,  slowly  soluble  in  acids.     Sesquioxide^  OsjOg,  has 


OSMIUM.  315 

already  been  noticed ;  it  is  generated  by  the  deoxidation  of  osmate  of  am- 
monia ;  it  is  black,  and  but  little  soluble  in  acids.  It  always  contains 
ammonia,  and  explodes  feebly  when  heated.  Binoxide  of  osmium,  OsOj,  is  pre- 
pared by  strongly  heating  in  a  retort  a  mixture  of  carbonate  of  soda  and  the 
bichloride  of  osmium  and  potassium,  and  treating  the  residue  with  water,  and 
afterwards  with  hydrochloric  acid.  The  binoxide  is  a  black  powder,  insoluble 
in  acids,  and  burning  to  osmic  acid  when  heated  in  the  air.  Osmious  acid 
OsOj  is  known  only  in  combination.  On  adding  alcohol  to  a  solution  of 
osmate  of  potassa,  the  alcohol  is  oxidized  at  the  expense  of  the  osmic  acid, 
and  a  rose-red  crystalline  powder  of  osmite  of  potassa  is  produced.  On  at- 
tempting to  separate  the  acid,  it  is  decomposed  into  the  binoxide  and  osmic 
acid.  Osmic  acid,  OSO4,  is  by  far  the  most  important  and  interesting  of  the 
oxides  of  this  metal.  It  is  prepared  by  heating  osmium  in  a  current  of  pure 
oxygen  gas ;  it  condenses  in  the  cool  part  of  the  tube  in  which  the  experi- 
ment is  made  in  colourless  transparent  crystals.  Osmic  acid  melts  and  even 
boils  below  212°  (100°C) ;  its  vapour  has  a  peculiar  offensive  odour,  and  is 
exceedingly  irritating  and  dangerous.  Water  slowly  dissolves  this  substance. 
It  has  acid  properties,  and  combines  with  bases.  Nearly  all  the  metals  pre- 
cipitate osmium  from  a  solution  of  osmic  acid.  By  the  action  of  ammonia 
on  osmic  acid,  a  new  acid  has  been  formed,  containing  osmium,  nitrogen, 
and  oxygen.  It  has  been  called  osman-osmic  acid  or  osmamic  acid.  Some 
doubts  are  hanging  over  the  formula  of  this  substance.  It  produces  salts 
with  many  bases. 

Chlorides  of  osmium.  —  ProiocMoride,  OsCl,  is  a  dark  green  crystalline 
substance,  formed  by  gently  heating  osmium  in  chlorine  gas.  It  is  soluble 
in  a  small  quantity  of  water,  with  green  colour,  but  decomposed  by  a  large 
quantity  into  osmic  and  hydrochloric  acids  and  metallic  osmium.  It  forms 
double  salts  with  the  metallic  chlorides.  The  sesquichloride,  Os^Clj,  has  not 
been  isolated ;  it  exists  in  the  solution  obtained  by  dissolving  the  sesquioxide 
in  hydrochloric  acid.  Bichloride,  OsClg,  in  combination  with  chloride  of 
potassium,  is  produced  when  a  mixture  of  equal  parts  metallic  osmium  and 
the  last-named  salt  is  strongly  heated  in  chlorine  gas.  It  forms  fine  red  oc- 
tahedral crystals,  containing  OsClj-j-KCl. 

Osmium  combines  also  with  sulphur  and  with  phosphorus. 


PART  III. 

ORGANIC   CHEMISTRY. 


INTRODUCTION. 


Organic  substances,  -whether  directly  derived  from  the  vegetable  or  ani- 
mal kingdom,  or  produced  by  the  subsequent  modification  of  bodies  which 
thus  originate,  are  remarkable  as  a  class  for  a  degree  of  complexity  of  con- 
stitution far  exceeding  that  observed  in  any  of  the  compounds  yet  described. 
And  yet  the  number  of  elements  which  enter  into  the  composition  of  these 
substances  is  extremely  limited  ;  very  few,  comparatively  speaking,  contain 
more  than  four,  viz.,  carbon,  hydrogen,  oxygen,  and  nitrogen;  sulphur  and 
phosphorus  are  occasionally  associated  with  these  in  certain  mineral  pro- 
ducts ;  and  compounds  containing  chlorine,  bromine,  iodine,  arsenic,  anti- 
mony, zinc,  &c.,  have  been  formed  by  artificial  means.  This  paucity  of 
elementary  bodies  is  compensated  by  the  very  peculiar  and  extraordinary 
properties  of  the  four  first-mentioned,  which  possess  capabilities  of  combi- 
nation to  which  the  remaining  elements  are  strangers.  There  appears  to  be 
absolutely  no  limit  to  the  number  of  definite,  and  often  crystallizable,  sub- 
stances which  can  be  thus  generated,  each  marked  by  a  perfect  individuality 
of  its  own. 

The  mode  of  association  of  the  elements  of  organic  substances  is  in  gene- 
ral altogether  different  from  that  so  obvious  in  the  other  division  of  the 
science.  The  latter  is  invariably  characterized  by  what  may  be  termed  a 
binary  plan  of  combination,  union  taking  place  between  pairs  of  elements, 
and  the  compounds  so  produced  again  uniting  themselves  to  other  compound 
bodies  in  the  same  manner.  Thus,  copper  and  oxygen  combine  to  oxide  of 
copper,  potassium  and  oxygen  to  potassa,  sulphur  and  oxygen  to  sulphuric 
acid ;  sulphuric  acid,  in  its  turn,  combines  both  with  oxide  of  copper  and  oxide 
of  potassium,  generating  a  pair  of  salts,  which  are  again  capable  of  uniting 
to  form  the  doiible  compound,  GuOjSOj-j-KOjSOg. 

The  most  complicated  products  of  inorganic  chemistry  may  be  thus  shown 
to  be  built  up  by  this  repeated  pairing  on  the  part  of  their  constituents. 
With  organic  bodies,  however,  the  case  is  strikingly  different ;  no  such  ar- 
rangement can  here  be  traced.  In  sugar,  CigHuOj,,  or  morphine,  C34Hj9N0g, 
or  the  radical  of  bitter  almond  oil,  C,4H502,  and  a  multitude  of  similar  cases, 
the  elements  concerned  are,  as  it  were,  bound  up  together  into  a  single 
whole,  which  can  enter  into  combination  with  other  substances,  and  be  thence 
disengaged  with  properties  unaltered. 

A  curious  consequence  of  this  peculiarity  is  to  be  found  in  the  compara- 
tively instable  character  of  organic  compounds,  and  their  general  proneness 
to  decomposition  and  change,  when  the  balance  of  opposing  forces,  to  which 
they  owe  their  existence,  becomes  deranged  by  some  external  cause. 

If  a  complex  inorganic  substance  be  attentively  considered,  it  will  usually 
be  found  that  the  elements  are  combined  in  such  a  manner  as  to  satisfy  the 
most  powerful  affinities,  and  to  give  rise  to  a  state  of  very  considerable  per- 
manence and  durability     But  in  the  case  of  an  organic  substance  coiitaininfj 

(31G) 


y^^-y- 


INTRODUCTI(#>^    TO   ORGANIC   CHEiMISTRY.  317 

three  or  four  elements  associated  in  the  way  described,  this  is  very  far  from 
being  true :  the  carbon  and  oxygen  strongly  tend  to  unite  to  form  carbonic 
acid ;  the  hydrogen  and  oxygen  attract  each  other  in  a  powerful  manner, 
and  the  nitrogen,  if  that  body  be  present,  also  contributes  its  share  to  these 
internal  sources  of  weakness  by  its  disposition  to  generate  ammonia.  While 
the  opposing  forces  remain  exactly  balanced,  the  integrity  of  the  compound 
is  preserved;  but  the  moment  one  of  them,  from  some  accidental  cause, 
acquires  preponderance  over  the  rest,  equilibrium  is  destroyed  and  the 
organic  principle  breaks  up  into  two  or  more  new  bodies  of  simpler  and  more 
permanent  constitution.  The  agency  of  heat  produces  this  effect  by 
exalting  the  attraction  of  oxygen  for  hydrogen  and  carbon ;  hence  the  almost 
universal  destructibility  of  organic  substances  by  a  high  temperature.  Mere 
molecular  disturbance  of  any  kind  may  cause  destruction  when  the  insta- 
bility is  very  great. 

As  a  general  rule,  it  may  be  assumed  that  those  bodies  which  are  most 
complex  from  the  number  of  elements,  and  the  want  of  simplicity  in  their 
equivalent  relations,  are  by  constitution  weakest,  and  least  capable  of  resist- 
ing the  action  of  disturbing  forces ;  and  that  this  susceptibility  of  change 
diminishes  with  increased  simplicity  of  structure,  until  it  reaches  its  minimum 
in  those  bodies  which,  like  the  carbides  of  hydrogen,  like  cyanogen,  and 
oxalic  acid,  connect,  by  imperceptible  gradations,  the  organic  and  the  mineral 
departments  of  chemical  science. 

The  definite  organic  principles  of  the  vegetable  and  animal  kingdoms  form 
but  a  very  small  proportion  of  the  immense  mass  of  compounds  included 
within  the  domain  of  organic  chemistry :  by  far  the  greater  number  of  these 
are  produced  by  modifying  by  suitable  means  the  bodies  furnished  by  the 
plant  or  the  animal,  and  which  have  themselves  been  formed  from  the 
elements  of  the  air  by  processes  for  the  most  part  unknown,  carried  on  under 
the  control  of  vitality.  Unlike  these  latter,  the  artificial  modifications 
referred  to,  by  oxidation,  by  the  action  of  other  powerful  reagents,  by  the 
influence  of  heat,  and  by  numerous  other  sources  of  disturbance,  are,  for 
the  most  part,  changes  of  descent  in  order  of  complexity,  new  products  being 
thus  generated  more  simple  in  constitution  and  more  stable  in  character  than 
the  bodies  from  which  they  were  derived.  These,  in  turn,  by  repetition  of 
such  treatment  under  perhaps  varied  circumstances,  may  be  broken  «p  into 
other  and  still  simpler  organic  combinations  ;  until  at  length  the  binary 
compounds  of  inorganic  chemistry,  or  bodies  so  allied  to  them  that  they  may 
be  placed  indifferently  in  either  group,  ai'C  by  such  means  reached. 

Organic  Substitution-products :  Law  of  Substitution. — The  study  of  the  action 
of  chlorine,  bromine,  iodine,  and  nitric  acid  upon  various  organic  substances 
has  led  to  the  discovery  of  a  very  remarkable  law  regulating  the  formation 
of  chlorinetted  and  other  analogous  compounds,  which,  without  being  of 
necessity  absolute  in  every  case,  is  yet  of  sufficient  generality  and  import- 
ance to  require  careful  consideration.  This  peculiar  mode  of  action  consists 
in  the  replacement  of  the  hydrogen  of  the  organic  substance  by  chlorine, 
bromine,  iodine,  the  elements  of  hyponitric  acid,  and  more  rarely  other  sub- 
stances of  the  same  class,  equivalent  for  equivalent,  without  the  destruction 
of  the  primitive  type  or  constitution  of  the  compound  so  modified.  The 
hydrogen  thus  removed  takes  of  course  the  form  of  hydrochloric  or  hydro- 
bromic  acid,  &c.,  or  that  of  water,  by  combination  with  another  portion  of 
the  active  body.  Strange  as  it  may  appear,  and  utterly  opposed  to  the  ordi- 
nary views  of  the  functions  of  powerful  salt-radicals,  this  loss  of  hydrogen 
and  assumption  of  the  new  element  do  actually  occur  with  a  great  variety 
of  substances  belonging  to  different  groups  with  comparatively  trifling  dis 
turbance  of  physical  and  chemical  properties ;  the  power  of  saturation,  the 
density  of  the  vapour,  and  other  pecularities  of  the  original  substance  remain 
27* 


518  INTEODUCTION    TO 

the  same,  saving  the  modification  they  may  suffer  from  the  difference  of  the 
equivalent  weights  of  hydrogen  and  the  bodies  by  which  it  is  replaced. 

This  change  may  take  place  by  several  successive  steps,  giving  rise  to  a 
series  of  substitution-compounds,  which  depart  more  and  more  in  properties 
from  the  original  substance  with  each  successive  increase  in  the  proportion 
of  the  replacing  body.  The  substitution  may  even  be  total,  the  whole  of  the 
hydrogen  being  lost,  and  its  place  supplied  by  a  similar  number  of  equiva- 
lents of  the  new  element.  And  even  in  these  extreme  cases,  of  very  common 
occurrence,  however,  with  one  class  of  substances,  the  resulting  compound 
retains  generally  the  stamp  of  its  origin. 

Although  numerous  examples  of  these  changes  will  be  found  described  in 
detail  in  the  following  pages,  it  will  be  well  perhaps  to  mention  here  two  or 
three  oases  by  way  of  illustration. 

Dutch-liquid,  the  compound  formed  by  the  union  of  equal  measures  of 
olefiant  gas  and  chlorine,  containing  C4H4CI2,  is  affected  by  chlorine  in 
obedience  to  the  law  of  substitution ;  one,  two,  three,  four  equivalents  of 
hydrogen  being  successively  removed  by  the  prolonged  action  of  the  gas 
aided  by  sunshine,  and  one,  two,  three,  or  four  equivalents  of  chlorine  intro- 
duced in  place  of  the  hydrogen  withdrawn  as  hydrochloric  acid.  In  the  last 
product,  the  sesquichloride  of  carbon,  C4CI5,  the  replacement  is  total;  the 
intermediate  products  are  volatile  liquids  not  differing  very  much  in  general 
characters  from  Dutch-liquid  itself.  A  great  number  of  compound  ethers 
of  the  ethyl-  and  methyl-series  are  attacked  by  chlorine  and  bromine  in  a 
similar  manner ;  indeed,  the  majority  of  the  examples  of  the  law  in  question 
are  to  be  found  in  the  history  of  this  class  of  bodies. 

Concentrated  acetic  acid,  placed  in  a  vessel  of  dry  chlorine  and  exposed  to 
the  sun,  gives  rise  to  chloracetic  acid,  containing  €401303,110,  and  in  which, 
consequently,  the  whole  hydrogen  of  the  real  acid  is  replaced  by  chlorine. 
Chloracetic  acid  is  a  stable  substance,  of  strong  acid  characters,  and  forms 
a  series  of  salts,  some  of  which  bear  no  slight  resemblance  to  the  normal  ace- 
tates. 

Basic  substitution-products  have  been  obtained  indirectly;  chloraniline, 
bromaniline,  and  iodaniline  are  the  most  striking  examples.  These  will  be 
found  fully  described  in  the  sections  on  organic  bases. 

The  action  of  fuming  nitric  acid  upon  organic  substances  very  commonly 
indeed  gives  rise  to  substitution-products  containing  the  elements  of  hypo- 
nitric  acid,  NO4,  in  place  of  hydrogen.  The  benzoyl-compounds,  and  several 
of  the  essential  oils  natural  and  derived  from  resins,  will  be  found  to  furnish 
illustrations. 

In  formulsB  representing  substitution-compounds  retaining  some  hydrogen, 
the  practice  is  often  adopted  of  placing  the  substituting  body  beneath  or  be- 
sides this  residual  hydrogen,  and  uniting  them  by  a  bracket  on  each  side. 
Thus,  the  formulae  of  the  first  two  products  of  the  action  of  chlorine  on  Dutch- 
liquid  are  thus  written : — 

C4  {  ^{  }  Cl„  and  C4  {  ^j2  }  CI2.  or  C4,  (H3CI)  Cl^  and  C4  (H.Cl^)  CI,. 

And  pyroxlin,  or  gun-cotton,  which  is  supposed  to  be  a  substitution-product 
from  lignin,  C^^^O^q,  having  6  equivalents  of  hydrogen  replaced  by  the  ele- 
ments of  hyponitric  acid,  will  stand: — 

^^^    {  5NO4  }  ^2o>  or  C,4  [H,5  (NO4),]  0^. 

Isomeric  bodies,  or  substances  different  in  properties,  yet  identical  in  com- 
position, are  of  constant  occurrence  in  organic  chemistry,  and  stand,  indeed, 
among  its  most  striking  and  peculiar  features.  Every  year  brings  to  light 
fresh  examples  of  compounds  so  related.     In  most  cases,  discordance  in  pT<»- 


ORGANIC    CHEMISTRY.  3K 

perties  is  fairly  and  properly  ascribed  to  difference  of  constitution,  the  ele- 
ments being  differently  arranged.  For  instance,  formic  ether  and  acetate  of 
methyl  are  isomeric,  both  containing  CgHg04  ;  but  then  the  first  is  supposed 
to  consist  of  formic  acid,  C2HO3,  combined  with  ether,  C4HgO ;  while  the 
second  is  imagined  in  accordance  with  the  same  views,  to  be  made  np  of  ace- 
tic acid,  C4H3O3,  and  the  ether  of  wood-spirit,  CjHgO.  And  this  method  of 
explanation  is  generally  suflBcient  and  satisfactory ;  when  it  can  be  shown 
that  a  difference  of  constitution,  or  even  a  difference  in  the  equivalent  num- 
bers, exists  between  two  or  more  bodies  identical  in  ultimate  composition, 
the  reason  of  their  discordant  characters  becomes  to  a  certain  extent  intelli- 
gible. 

Organic  bodies  may  be  thus  classified : — 

1.  Quasi-elementaTy  Substances,  and  their  compounds. — These  affect  the 
disposition  and  characters  of  the  true  elements,  and,  like  the  latter,  evince  a 
tendency  to  unite  on  the  one  hand  with  hydrogen  and  the  metals,  and  on  the 
other  with  chlorine,  iodine,  and  oxygen.  The  former  are  designated  organic 
gait-radicals,  and  the  latter  organic  salt-basyles.  Few  of  either  kind  have  been 
yet  isolated,  and  it  is  very  possible  that  very  many  of  them  are  unable  to 
exist  in  a  separate  state.  Some  of  these  quasi-elements  are  among  the  most 
important  and  interesting  substances  in  organic  chemistry. 

2.  Organic  Salt-bases,  not  being  the  oxides  of  known  radicals.  —  The  prin- 
cipal members  of  this  class  are  the  vegeto-alkalis ;  they  form  crystallizable 
compounds  with  acids,  organic  and  inorganic,  and  even  possess  in  some  cases 
a  distinct  alkaline  reaction  to  test-paper. 

3.  Organic  acids,  not  being  compounds  of  known  radicals. —  These  bodies 
are  very  numerous  and  important.  Many  of  them  have  an  intensely  sour 
taste,  redden  vegetable  blues,  and  are  almost  comparable  in  chemical  energy 
with  the  acids  of  mineral  origin. 

4.  Neutral  non-azotized  substances,  containing  oxygen  and  hydrogen  in  the 
proportions  to  form  water. — The  term  neutral,  as  applied  to  these  compounds, 
is  not  strictly  correct,  as  they  usually  manifest  feeble  acid  properties  by  com- 
bining with  metallic  oxides.  This  group  comprehends  the  sugars,  the  dif- 
ferent modifications  of  starch,  gum,  &c. 

5.  Neutral  azotized  substances ;  the  albuminous  principles  and  their  allies, 
the  great  components  of  the  animal  frame.  — These  are  in  the  highest  degree 
complex  in  constitution,  and  are  destitute  of  the  faculty  of  crystallization. 

6.  Carbides  of  Hydrogen,  their  oxides  and  derivatives. 

7.  Fatty  bodies. 

8.  Compound  acids,  containing  the  elements  of  an  organic  substance  in  com- 
bination with  those  of  a  mineral  or  other  acid.  —  These  bodies  form  a  largo 
and  very  interesting  class,  of  which  sulphovinic  acid  may  be  taken  as  the 
type  or  representative. 

9.  Colouiing  principles f  and  other  substances  not  referable  to  either  of  the 
preceding  classes. 

The  action  of  heat  on  organic  substances  presents  many  important  and 
interesting  points,  of  which  a  few  of  the  more  prominent  maybe  noticed. 
Bodies  of  simple  constitution  and  of  some  permanence,  which  do  not  sublime 
unchanged,  as  many  of  the  organic  acids,  yield,  when  exposed  to  a  high,  but 
regulated  temperature,  in  a  retort,  new  compounds,  perfectly  definite  and 
often  crystallizable,  which  partake,  to  a  certain  extent,  of  the  properties  of 
the  original  substance :  the  numerous  pyro-acids,  of  which  many  examples 
will  occur  in  the  succeeding  pages,  are  thus  produced.  Carbonic  acid  and 
water  are  often  eliminated  under  these  circumstances.  If  the  heat  be  sud- 
denly raised  to  redness,  then  the  regularity  of  the  decomposition  vanishes, 
while  the  products  become  more  uncertain  and  more  numerous ;  carbonic 
acid  and  watery  vapor  are  succeeded  by  inflammable  gases  as  carbonic  oxide 


320  THE     ULTIMATE     ANALYSIS     OF 

and  carbonetted  hydrogen ;  oily  matter  and  tar  distil  over,  and  increase  in 
quantity  until  the  close  of  the  operation,  when  the  retort  is  found  to  contain, 
in  most  cases,  a  residue  of  charcoal.     Such  is  destructive  distillation. 

If  the  organic  substance  contain  nitrogen,  and  be  not  of  a  kind  capable 
of  taking  a  new  and  permanent  form  at  a  moderate  degree  of  heat,  then 
that  nitrogen  is  in  most  instances  partly  disengaged  in  the  shape  of  ammo- 
nia, or  substances  analogous  to  it,  partly  left  in  combination  with  the  carbo- 
naceous matter  in  the  distillatory  vessel.  The  products  of  dry  distillation 
thus  become  still  more  complicated 

A  much  greater  degree  of  regularity  is  observed  in  the  effects  of  heat  on 
fixed  organic  matters,  when  these  are  previously  mixed  with  an  excess  of 
strong  alkaline  base,  as  potassa  or  lime.  In  such  cases  an  acid,  the  nature 
of  which  is  chiefly  dependent  upon  the  temperature  applied,  is  produced,  and 
remains  in  union  with  the  base,  the  residual  element  or  elements  escaping 
in  some  volatile  form.  Thus,  benzoic  acid  distilled  with  hydrate  of  lime,  at 
a  dull  red-heat,  yields  carbonate  of  lime  and  a  bicarbide  of  hydrogen,  ben- 
zole ;  woody  fibre  and  caustic  potassa,  heated  to  a  very  moderate  tempera- 
ture, yield  ulmic  acid  and  free  hydrogen ;  with  a  higher  degree  of  heat, 
oxalic  acid  appears  in  the  place  of  the  ulmic ;  and,  at  the  temperature  of 
ignition,  carbonic  acid,  hydrogen  being  the  other  product. 

The  spontaneous  changes  denominated  decay  and  putrefaction,  to  which 
many  more  of  the  complicated  organic,  and,  more  particularly,  azotized  prin 
ciples  are  subject,  have  lately  attracted  much  attention.  By  the  expression 
decay,*  Liebig  and  his  school  understand  a  decomposition  of  moist  organic 
matter,  freely  exposed  to  the  air,  by  the  oxygen  of  which  it  is  gradually 
burned  and  destroyed,  without  sensible  elevation  of  temperature ;  the  term 
putrefaction,  on  the  other  hand,  is  limited  to  changes  occurring  in  and  be- 
neath the  surface  of  water,  the  effect  being  a  mere  transposition  of  ele- 
ments, or  metamorphosis  of  the  organic  body.  The  conversion  of  sugar  into 
alcohol  and  carbonic  acid  furnishes,  perhaps,  the  simplest  case  of  the  kind. 
It  is  proper  to  remark,  however,  that  contact  of  oxygen  is  indispensable,  in 
the  first  instance,  to  the  change,  which,  when  once  begun,  proceeds,  without 
the  aid  of  any  other  substance  external  to  the  decomposing  body,  unless  it 
be  water  or  its  elements.  Every  case  of  putrefaction  thus  begins  with  de- 
cay ;  and  if  the  decay  or  its  cause,  namely,  the  absorption  of  oxygen,  be 
prevented,  no  putrefaction  occurs.  The  most  putrescible  substances,  as  an- 
imal flesh  intended  for  food,  milk,  and  highly  azotized  vegetables,  are  pre 
served  indefinitely,  by  enclosure  in  metalKc  cases,  from  which  the  air  has 
been  completely  removed  and  excluded. 

Some  of  the  curious  phenomena  of  communicated  chemical  activity,  where 
a  decomposing  substance  seems  to  involve  others  in  destructive  change, 
which,  without  such  influence,  would  have  remained  in  a  permanent  and 
quiescent  state,  will  be  found  noticed  in  their  proper  places,  as  under  the 
head  of  Vinous  Fermentation.  These  actions  are  yet  very  obscure,  and  re- 
quire to  be  discussed  with  great  caution. 


THE  ULTIMATE  ANALYSIS  OP  OHGANTC  BODIES. 

A»  organic  substances  cannot  be  produced  at  will  from  their  elements,  the 
analytical  method  of  research  is  alone  applicable  to  the  investigation  of  their 
exact  chemical  composition ;  hence  the  ultimate  analysis  of  these  substances 
becomes  a  matter  of  great  practical  importance.  The  operation  is  always 
executed  by  causing  complete  combustion  of  a  known  weight  of  the  body  to 

»  Or  erema&iitsis,  that  is,  slow  burning. 


ORGANIC    BODIES.  821 

be  examined,  in  such  a  manner  that  the  carbonic  acid  and  water  produced 
shall  be  collected,  and  their  quantity  determined ;  the  carbon  and  hydrogen 
they  respectively  contain  may  from  these  data  be  easily  calculated.  When 
nitrogen,  sulphur,  phosphorus,  chlorine,  &c.,  are  present,  special  and  sepa- 
rate means  are  resorted  to  for  their  estimation. 

The  method  to  be  described  for  the  determination  of  the  carbon  and  hy- 
drogen owes  its  convenience  and  efficiency  to  the  improvements  of  Professor 
Liebig ;  it  has  superseded  all  other  processes,  and  is  now,  invariably  employed 
in  inquiries  of  the  kind.  With  proper  care,  the  results  obtained  are  wonder- 
fully correct;  and  equal,  if  not  surpass  in  precision,  those  of  the  best 
mineral  analyses.  The  principle  upon  which  the  whole  depends  is  the  fol- 
lowing :  —  When  an  organic  substance  is  heated  with  the  oxides  of  copper, 
lead,  and  several  other  metals,  it  undergoes  complete  combustion  at  the  ex- 
pense of  the  oxygen  of  the  oxide,  the  metal  being  at  the  same  time  reduced, 
either  completely  or  to  a  lower  state  of  oxidation.  This  effect  takes  place 
with  greatest  ease  and  certainty  with  the  black  oxide  of  copper,  which,  al- 
though unchanged  by  heat  alone,  gives  up  oxygen  to  combustible  matter 
with  extreme  facility.  When  nothing  but  carbon  and  hydrogen,  or  those  bo- 
dies together  with  oxygen,  are  present,  one  experiment  suffices ;  the  carbon 
and  hydrogen  are  determined  directly,  and  the  oxygen  by  difference. 

It  is  of  course  indispensable  that  the  substance  to  be  analyzed  should 
possess  the  physical  characters  of  purity,  otherwise  the  inquiry  cannot  lead 
to  any  good  result ;  if  in  the  solid  state,  it  must  also  be  freed  with  the  most 
scrupulous  care  from  the  moisture  which  many  substances  retain  with  great 
obstinacy.  If  it  will  bear  the  application  of  moderate  heat,  this  desiccation 
is  very  easily  accomplished  by  a  water  or  steam-bath ;  in  other  cases,  expo- 
sure at  common  temperatures  to  the  absorbent  powers  of  a  large  surface  of 
oil  of  vitriol  in  the  vacuum  of  an  air-pump  must  be  substituted. 

The  operation  of  weighing  the  dried  powder  is  conducted  in  a  narrow  open 
tube  (fig.  153),  about  2^  or  3  inches  long;  the  tube 
and  substance  are  weighed  together,  and,  when  the  Fig.  153. 

latter  has  been  removed,  the  tube  with  any  little 
adherent  matter  is  re- weighed.  This  weight,  sub- 
tracted from  the  former,  gives  the  weight  of  the  sub- 
stance employed  in  the  experiment.  As  only  5  or  6 
grains  are  used,  the  weighings  should  not  evolve  a 
greater  error  than  oW*^  P^^*  of  a  grain. 

The  protoxide  of  copper  is  best  made  from  the 
nitrate  by  complete  ignition  in  an  earthen  crucible : 
it  is  reduced  to  powder,  and  re-heated  just  before 
use,  to  expel  hygroscopic  moisture,  which  it  absorbs, 
even  while  warm,  with  avidity.  The  combustion  is 
performed  in  a  tube  of  hard  white  Bohemian  glass, 
having  a  diameter  of  0-4  or  0-5  inch,  and  in  length  varying  from  14  to  18 
inches  ;  this  kind  of  glass  bears  a  moderate  red-heat  without  becoming  soft 
enough  to  lose  its  shape.  One  end  of  the  tube  is  drawn  out  to  a  point,  as 
shown  in  fig.  154,  and  closed;  the  other  is  simply  heated  to  fuse  and  soften 
the  sharp  edges  of  the  glass.     The  tube  is  now  two-thirds  filled  with  the  ye» 

Fig.  154. 
Oxide  copper.  Mixture.  Oxide  copper. 


(^a 


322 


THE     ULTIMATE    ANALYSIS    OP 


warm  protoxide  of  copper,  nearly  the  whole  of  which  is  transferred  to  a 
small  porcelain  or  Wedgwood  mortar,  and  very  intimately  mixed  with  the 
organic  substance.  The  mixture  is  next  transferred  to  the  tube,  and  the 
mortar  rinsed  with  a  little  fresh  and  hot  oxide,  which  is  added  to  the  rest ; 
the  tube  is,  lastly,  filled  to  within  an  inch  of  the  open  end  with  oxide  from 
the  crucible.  A  few  gentle  taps  on  the  table  suffice  to  shake  together  the 
contents,  so  as  to  leave  a  free  passage  for  the  evolved  gases  from  end  to  end. 
The  arrangement  of  the  mixture  and  oxide  in  the  tube  is  represented  in  the 
sketch. 

The  tube  is  then  ready  to  be  placed  in  the  furnace  or  chauffer  :  this  latter 
is  constructed  of  thin  sheet-iron,  and  is  furnished  with  a  series  of  supports 
of  equal  height,  which  serve  to  prevent  flexure  in  the  combustion-tube  when 
softened  by  heat.     Fig.  155.     The  chauffer  is  placed  upon  flat  bricks  or  a 

Fig.  155. 


piece  of  stone,  so  that  but  little  air  can  enter  the  grating,  unless  the  whole 
be  purposely  raised.  A  slight  inclination  is  also  given  towards  the  extremity 
occupied  by  the  mouth  of  the  combustion-tube,  which  passes  through  a  hole 
provided  for  the  purpose. 

To  collect  the  water  produced  in  the  experiment,  a  small  light  tube  of  the 
form  represented  in  fig.  156,  filled  with  fragments  of  spongy  chloride  of  cal- 
cium, is  attached  by  a  perforated  cork,  thoroughly  dried,  to  the  open  ex- 


Fig.  156. 


Fig.  157. 


e=s=^^^ 


tremity  of  the  combustion-tube.  The  carbonic  acid  is  condensed  into  a  solu- 
tion of  caustic  potassa,  of  specific  gravity  1-27,  which  is  conttiined  in  a  small 
glass  apparatus  on  the  principle  of  a  Woulfe's  bottle,  shown  in  fig.  157. 
The  connection  between  the  latter  and  the  chloride  of  calcium-tube  is  com- 
pleted by  a  little  tube  of  caoutchouc,  secured  with  silk  cord.  Tlie  whole  is 
shown  in  fig.  158,  as  arranged  for  use.  Both  the  chloride  of  calcium-tube 
und  the  potass-apparatus  are  weighed  with  the  utmost  care  before  the  ex- 
periment. 

The  tightness  of  the  junctions  may  be  ascertained  by  slightly  rarefying 
the  included  air  by  sucking  a  few  bubbles  from  the  interior  'through  the 
liquid,  using  the  dry  lips,  or  better,  a  little  bent  tube  with  a  perforated  cork  : 
f  the  difference  of  the  level  of  the  liquid  in  the  two  limbs  of  the  potass- 


ORGANIC     BODIES. 


323 


apparatus  be  preserved  for  several  minutes,  the  joints  are  perfect.     Red- 
hot  charcoal  is  now  placed  around  the  anterior  portion  of  the  combustion- 
Fig.  158. 


Drawing  of  the  whole  arrangement. 

tube,  containing  the  pure  oxide  of  copper,  and  when  this  is  red-hot,  the  fire 
is  slowly  extended  towards  the  farther  extremity  by  shifting  the  moveable 
screen  ^,  represented  in  the  drawing.  The  experiment  must  be  so  conducted, 
that  an  uniform  stream  of  carbonic  acid  shall  enter  the  potass-apparatus  by 
bubbles  which  may  be  easily  counted :  when  no  nitrogen  is  present,  these 
bubbles  are  towards  the  termination  of  the  experiment  almost  completely 
absorbed  by  the  alkaline  liquid,  the  little  residue  of  air  alone  escaping.  In 
the  case  of  an  azotized  body,  on  the  contrary,  bubbles  of  nitrogen  gas,  pass 
through  the  potassa-solution  during  the  whole  process. 

When  the  tube  has  become  completely  heated  from  end  to  end,  and  no 
more  gas  is  disengaged,  but,  on  the  other  hand,  absorption  begins  to  be 
evident,  the  coals  are  removed  from  the  farther  extremity  of  the  combustion- 
tube,  and  the  point  of  the  latter  broken  off.  A  little  air  is  drawn  through 
the  whole  apparatus,  by  which  the  remaining  carbonic  acid  and  watery 
vapour  are  secured.  The  parts  are,  lastly,  detached,  and  the  chloride  of 
calcium  tube  and  potass-apparatus  re-weighed.  The  following  account  of  a 
real  experiment  will  serve  as  an  illustration  ;  the  substance  examined  was 
crystallized  sugar. 

Quantity  of  sugar  employed 4-750  grains. 

Potass-apparatus  weighed  after  experiment....   781-13 
•*  "  before  experiment..  773-82 

Carbonic  acid 7-31 

Chloride  of  calcium-tube  after  experiment 226-05 

"  "  before  experiment ...  223-30 

Water 2-75 

7-31  gr.  carbonic  acid=l-994  gr.  carbon:  and  2-75  gr.  water=0-3056  gx 
hydrogen ;  or  in  100  parts  of  sugar,' 


•  The  theoretical  composition  of  sugar  CuHnOu,  reckoned  to  100  parts  gives  — 

Carbon 42-11 

Hydrogen 6-43 

Oxygen 61-46 

lOO-OO 


324  THE    ULTIMATE    ANALYSIS    OP 

CarI)on 41-98 

Hydrogen 6*43 

Oxygen,  by  diflFerence 51-59 

100-00 

When  the  organic  substances  cannot  be  mixed  with  the  protoxide  of  copper 
in  the  manner  described,  the  process  must  be  slightly  modified  to  meet  the 
particular  case.  If,  for  example,  a  volatile  liquid  is  to  be  examined,  it  is 
enclosed  in  a  little  glass  bulb  with  a  narrow  stem,  which  is  weighed  before 
and  after  the  introduction  of  the  liquid,  the  point  being  hermetically  sealed. 
The  combustion-tube  must  have,  in  this  case,  a  much  greater  length ;  and, 
as  the  protoxide  of  copper  cannot  be  introduced  hot,  it  must  be  ignited  and 
cooled  out  of  contact  with  the  atmosphere,  to  pre- 
Fig.  159.  "^cnt  absorption  of  watery  vapour.     This  is  most 

conveniently  eflfected  by  transferring  it,  in  a  heated 
state,  to  a  large  platinum  crucible,  to  which  a 
close-fitting  cover  can  be  adapted.  When  quite 
cold,  the  cover  is  removed,  and  instantly  replaced 
by  a  dry  glass  funnel,  by  the  assistance  of  which 
the  oxide  may  be  directly  poured  into  the  com- 
^^  bustion-tube,  with  mere  momentary  exposure  to 

the  air.  A  little  oxide  is  put  in,  then  the  bulb, 
with  its  stem  broken  at  a,  fig.  159,  a  file-scratch 
having  been  previously  made ;  and  lastly,  the  tube 
is  filled  with  the  cold  and  dry  protoxide  of  copper. 
^  It  is   arranged  in  the  chauffer,  the  chloride  of 

calcium  tube  and  potass-apparatus  adjusted,  and 
then,  some  six  or  eight  inches  of  oxide  having  been  heated  to  redness,  the 
liquid  in  the  bulb  is,  by  the  approximation  of  a  hot  coal,  expelled,  and  slowly 
converted  into  vapour,  which,  in  passing  over  the  hot  oxide,  is  completely 
burned.  The  experiment  is  then  terminated  in  the  usual  manner.  Fusible 
fatty  substances,  and  volatile  concrete  bodies,  as  camphor,  require  rather 
different  management,  which  need  not  be  here  described. 

Protoxide  of  copper,  which  has  been  used,  may  be  easily  restored  by 
moistening  with  nitric  acid,  and  ignition  to  redness;  it  becomes,  in  fact, 
rather  improved  than  otherwise,  as  after  frequent  employment  its  density  is 
increased,  and  its  troublesome  hygroscopic  powers  diminished.  For  sub- 
stances which  are  very  difficult  of  combustion,  from  the  large  proportion  of 
carbon  they  contain,  and  for  compounds  into  which  chlorine  enters  as  a  con- 
stituent, fused  and  powdered  chromate  of  lead  is  very  advantageously  sub- 
stituted for  the  protoxide  of  copper,  Chromate  of  lead  freely  gives  up 
oxygen  to  combustible  matters,  and  even  evolves,  when  strongly  heated,  a 
little  of  that  gas,  which  thus  ensures  the  perfect  combustion  of  the  organic 
body. 

/Inah/sis  of  azotized  Substances. — The  presence  of  nitrogen  in  an  organic 
compound  is  easily  ascertained  by  heating  a  small  portion  with  solid  hydrate 
of  potassa  in  a  test-tube  ;  the  nitrogen,  if  present,  is  converted  into  ammo- 
nia, which  may  be  recognized  by  its  odour  and  alkaline  reaction.  There  are 
several  methods  of  determining  the  proportion  of  nitrogen  in  azotized  organic 
substances,  the  experimenter  being  guided  in  his  choice  of  means  by  the 
nature  of  the  substance  and  its  comparative  richness  in  that  element.  The 
carbon  and  hydrogen  are  first  determined  in  the  usual  manner,  a  longer  tube 
than  usual  is  employed,  and  four  or  five  inches  of  its  anterior  portion  filled 
witn  spongy  metallic  copper,  made  by  reducing  the  protoxide  by  hydrogen ; 
this  serves  to  decompose  any  nitrous  acid  or  biD  oxide  of  nitrogen,  which  may 


ORGANIC    BODIES. 


325 


h»  formed  in  the  act  of  combustion.  During  the  experiment  some  idea  of 
thtt  abundance  or  paucity  of  the  nitrogen  may  be  formed  from  the  number 
of  bubbles  of  incondensible  gas  which  traverse  the  solution  of  potassa. 

In  the  case  of  compounds  abounding  in  nitrogen,  and  readily  burned  by 
protoxide  of  copper,  a  method  may  be  employed,  which  is  very  easy  of  execu- 
tion ;  this  consists  in  determining  the  ratio  borne  by  the  liberated  nitrogen 
to  the  carbonic  acid  produced  in  the  combustion.  A  tube  of  hard  glass,  of 
the  usual  diameter,  and  about  15  inches  long,  is  sealed  at  one  end;  a  little 
of  the  organic  substance,  mixed  with  protoxide  of  copper,  is  introduced,  and 
allowed  to  occupy  about  two  inches  of  the  tube ;  about  as  much  pure  oxide 
is  placed  over  it,  and  then  another  portion  of  a  similar  mixture ;  after  which 
the  tube  is  filled  up  with  a  second  and  larger  portion  of  the  pure  oxide,  and 
a  quantity  of  spongy  metallic  copper.  A  short  bent  tube,  made  moveable 
by  a  caoutchouc  joint,  is  fitted  by  a  perforated  cork,  and  made  to  dip  into  a 
mercurial  trough,  while  the  combustion-tube  itself  rests  in  the  chauffer. 
(Fig.  160.) 

Fig.  160. 


Fire  is  first  applied  to  the  anterior  part  of  the  tube  containing  the  metal 
and  unmixed  oxide,  and,  when  this  is  red-hot,  to  the  extreme  end.     Com- 
bustion of  the  first  portion  of  the  mixture  takes  place,  the  gaseous  products 
sweeping  before  them  nearly  the  whole  of  the  air  of  the  apparatus,    j-jg.  igl. 
When  no  more  gas  issues,  the  tube  is  slowly  heated  by  half  an  inch 
at  a  time,  in  the  usual  manner,  and  all  the  gas  very  carefully  col- 
lected in  a  graduated  jar,  until  the  operation  is  at  an  end.     The 
volume  is  then  read  off,  and  some  strong  solution  of  caustic  po- 
tassa thrown  up  into  the  jar  by  a  pipette  with  a  curved  extremity. 
(Fig.  161.)   When  the  absorption  is  complete,  the  residual  volume 
of  nitrogen  is  observed,  and  compared  with  that  of  the  mixed 
gases,  proper  correction  being  made  for  difference  of  level  in  the 
mercury,  and  from  these  data  the  exact  proportion  borne  by  the 
nitrogen  to  the  carbon  can  be  at  once  determined.' 

If  the  proportion  of  nitrogen  be  but  small,  the  error  from  the  ni- 
trogen of  the  residual  atmospheric  air  becomes  so  great  as  to  de- 
stroy all  confidence  in  the  result  of  the  experiment ;  and  the  same 
thing  happens  when  the  substance  is  incompletely  burned  by  pro- 
toxide of  copper;   other  means  must  then  be   employed.     The 

*  Volumes  of  the  two  gases  represents  equivalents;  for 

100  cubic  inches  carbonic  acid  weigh  47-26  grains. 
100  „  nitrogen        „  30-14 

47-26    :    30-14    =    22    :    14-01 

The  last  two  term?  are  the  equivalent  numbers:  one  equiralent  of  carbonic  v>i  lOot 
on*  equivalent  of  carbon, 
28 


U 


326  THE    ULTIMATE    ANALYSIS    OP 

absolute  method  of  determination,  also  known  by  the  name  of  Dumas's  me- 
thod, may  be  had  recourse  to  when  the  foregoing,  or  comparative  method, 
fails  from  the  first  cause  mentioned ;  it  gives  excellent  results,  and  is  appli- 
cable to  all  azotized  substances. 

A  tube  of  good  Bohemian  glass,  ^8  inches  long,  is  securely  sealed  at  one 
end ;  into  this  enough  dry  bicarbonate  of  soda  is  put  to  occupy  6  inches.  A 
little  pure  protoxide  of  copper  is  next  introduced,  and  afterwards  the  mix- 
ture of  oxide  and  organic  substance,  the  weight  of  the  latter,  between  4-5 
and  9  grains,  in  a  dry  state,  having  been  correctly  determined.  The  remain- 
der of  the  tube,  amounting  to  nearly  one-half  of  its  length,  is  then  filled  up 
with  pure  protoxide  of  copper  and  spongy  metal,  and  a  round  cork,  perfo- 
rated by  a  piece  of  narrow  tube,  is  securely  adapted  to  its  mouth.  This 
tube  is  connected  by  means  of  a  caoutchouc  joint  with  a  bent  delivery  tube, 
a,  fig.  162,  and  the  combustion-tube  arranged  in  the  furnace.     A  few  coals 

Fig.  162. 


ar  e  now  applied  to  the  farther  end  of  the  tube,  so  as  to  decompose  a  portion 
of  the  bicarbonate  of  soda,  the  remainder  of  the  carbonate  as  well  as  of  the 
other  part  of  the  tube  being  protected  from  the  heat  by  a  screen  n.  The 
current  of  carbonic  acid  thus  produced  is  intended  to  expel  all  the  air  from 
the  apparatus.  In  order  to  ascertain  that  this  object,  on  which  the  success 
of  the  whole  operation  depends,  is  accomplished,  the  delivery-tube  is  de- 
pressed under  the  level  of  a  mercurial  trough,  and  the  gas,  which  is  evolved, 
collected  in  a  test-tube  filled  with  cwicentrated  potassa-solution.  If  the  gas 
be  perfectly  absorbed,  or,  after  the  introduction  of  a  considerable  quantity, 
only  a  minute  bubble  be  left,  the  air  may  be  considered  as  expelled.  The  next 
step  is  to  fill  a  graduated  glass-jar  two-thirds  with  mercury  and  one-third 
with  a  strong  solution  of  potassa,  and  to  invert  it  over  the  delivery-tube,  as 
represented  in  fig.  162. 

This  done,  fire  is  applied  to  the  tube,  commencing  at  the  front  end,  and 
gradually  proceeding  to  the  closed  extremity,  which  yet  contains  some  unde- 
oomposed  bicarbonate  of  soda.  This,  when  the  fire  at  length  reaches  it, 
yields  up  carbonic  acid,  which  chases  forward  the  nitrogen  lingering  in  the 
tube.  The  carbonic  acid  generated  during  the  combustion  is  wholly  absorbed 
by  the  potassa  in  the  jar,  and  nothing  is  left  but  the  nitrogen.  When  the 
operation  is  at  an  end,  the  jar,  with  its  contents,  is  transferred  to  a  vessel 
of  water,  and  the  volume  of  the  nitrogen  read  off.  This  is  properly  corrected 
for  temperature,  pressure,  and  aqueous  vapour,  and  its  weight  determined 
by  calculation.  When  the  operation  has  been  very  successful,  and  all  pre- 
cautions minutely  observed,  the  result  still  leaves  an  error  in  excess,  amount- 
ing to  0-3  or  0-5  per  cent.,  due  to  the  residual  air  of  the  apparatus,  or  that 
ooiidensed  into  the  pores  of  the  protoxide  of  copper. 

A  most  elegant  "process  for  estimating  nitrogen  in  all  organic  compounds, 
tfTcept  those  containing  the  nitrogen  in  the  form  of  nitrous,  hyponitric  and 


ORGANIC    BODIES.  827^ 

nitric  acids,  has  been  put  into  practice  by  MM.  Will  and  Varrentrapp.  When 
a  non-azotized  organic  substance  is  lieated  to  redness  with  a  large  excess  of 
hydrate  of  potassa  or  soda,  it  suffers  complete  and  speedy  combustion  at  the 
expense  of  the  water  of  the  hydrate,  the  oxygen  combining  with  the  carbon 
of  the  organic  matter  to  carbonic  acid,  which  is  retained  by  the  alMlli,  while 
its  hydrogen,  together  with  that  of  the  substance,  is  disengaged,  sometimes 
in  union  with  a  little  carbon.  The  same  change  happens  when  nitrogen  is 
present,  but  with  this  addition :  the  whole  of  the  nitrogen  thus  abandoned 
combines  with  a  portion  of  the  liberated  hydrogen  to  form  ammonia.  It  is, 
evident,  therefore,  that  if  this  experiment  be  made  on  a  weighed  quantity 
of  matter,  and  circumstances  allow  the  collection  of  the  whole  of  the  ammonia 
thus  produced,  the  proportion  of  nitrogen  can  be  easily  calculated. 

An  intimate  mixture  is  made  of  1  part  caustic  soda,  and  2  or  3  parts  quick- 
lime, by  slaking  lime  of  good  quality  with  the  proper  proportion  of  strong 
caustic  soda,  drying  the  mixture  in  an  iron  vessel,  and  then  heating  it  to 
strong  redness  in  an  earthen  crucible.  The  ignited  mass  is  rubbed  to  powder 
in  a  warm  mortar,  and  carefully  preserved  from  the  air.  The  lime  is  useful 
in  many  ways :  it  diminishes  the  tendency  to  deliquescence  of  the  alkali,  fa- 
cilitates mixture  with  the  organic  substance,  and  prevents  fusion  and  lique- 
faction. A  proper  quantity  of  the  substance  to  be  analyzed,  from  5  to  10 
grains  namely,  is  dried  and  accurately  weighed  out ;  this  is  mixed  in  a  warm 
porcelain  mortar  with  enough  of  the  soda-lime  to  fill  two-thirds  of  an  ordi- 
nary combustion-tube,  the  mortar  being  rinsed  with  a  little  more  of  the 
alkaline  mixture,  and,  lastly,  with  a  small  quantity  of  powdered  glass,  which 
completely  removes  everything  adherent  to  its  surface ;  the  tube  is  then  filled 
to  within  an  inch  of  the  open  end  with  the  lime-mixture,  and  arranged  in 
the  chauffer  in  the  usual  manner.  The  ammonia  is  collected  in  a  little  ap- 
paratus of  three  bulbs  (fig.  163)  containing  moderately  strong  hydrochloric 

Fig.  163. 


acid,  attached  by  a  cork  to  the  combustion-tube.  Matters  being  thus  ad- 
justed, fire  is  applied  to  the  tube  commencing  with  the  anterior  extremity. 
When  ignited  throughout  its  whole  length,  and  when  no  more  gas  issues  from 
the  apparatus,  the  point  of  the  tube  is  broken,  and  a  little  air  drawn  through 
the  whole.  The  acid  liquid  is  then  emptied  into  a  capsule,  the  bulbs  rinsed 
into  the  same,  first  with  a  little  alcohol,  and  then  repeatedly  with  distilled 
water ;  an  excess  of  pure  bichloride  of  platinum  is  added,  and  the  whole 
evaporated  to  dryness  in  a  water-bath.  The  dry  mass,  when  cold,  is  treated 
with  a  mixture  of  alcohol  and  ether,  which  dissolves  out  the  superfluous  bi- 
chloride of  platinum,  but  leaves  untouched  the  yellow  crystalline  double 
chloride  of  platinum  and  ammonium.  The  latter  is  collected  upon  a  small 
weighed  filter,  washed  with  the  same  mixture  of  alcohol  and  ether,  dried  at 
212°  (100°C),  and  weighed ;  100  parts  correspond  to  6-272  parts  of  nitrogen  ; 
or,  the  salt  with  its  filter  may  be  very  carefully  ignited,  and  the  filter  burned 
in  a  platinum  crucible,  and  the  nitrogen  reckoned  from  the  weight  of  the 
spongy  metal,  100  parts  of  that  substance  corresponding  to  14-18  parts  of 
nitrogen.     The  former  plan  is  to  be  preferred  in  most 


228      ULTIMATE    ANALYSIS    OF    ORGANIC    BODIES. 

Bodies  very  rich  in  nitrogen,  as  urea,  must  be  mixed  with  about  an  equwv 
quantity  of  pure  sugar,  to  furnisli  incondensible  gas,  and  thus  diminish  the 
violence  of  the  absorption  which  otherwise. occurs;  and  the  same  precaution 
must  be  taken,  for  a  different  reason,  with  those  which  contain  little  or  no 
hydrogelH 

A  modification  of  this  process  has  been  lately  suggested  by  M.  P^ligot, 
which  is  very  convenient  if  a  large  number  of  nitrogen-determinations  are 
to  be  made.  By  this  plan  the  ammonia,  instead  of  being  received  in  hydro- 
chloric acid,  is  conducted  into  a  known  volume  (from  ^  to  1  cubic  inch)  of 
a  standard  solution  of  sulphuric  acid,  contained  in  the  ordinary  nitrogen- 
b\ilbs.  After  the  combustion  is  finished,  the  acid  containing  the  ammonia  is 
poured  out  into  a  beaker,  coloui-ed  with  a  drop  of  tincture  of  litmus,  and 
then  neutralized  with  a  standard  solution  of  soda  in  water  or  of  lime  in 
sugar-water,  the  point  of  neutralization  becoming  perceptible  by  the  sudden 
appearance  of  a  blue  tint.  The  lime-solution  is  conveniently  poured  out 
from  the  graduated  glass- tube,  fig.  136,  described  under  the  head  of  alkali- 
metry (page  227).  The  volume  of  lime-solution  necessary  to  neutralize  the 
same  amount  of  acid,  which  is  used  for  condensing  the  ammonia,  having 
been  ascertained  by  a  preliminary  experiment,  it  is  evident  that  the  differ- 
ence of  the  quantities  used  in  the  two  experiments  gives  the  ammonia  col- 
lected during  the  combustion  in  the  acid ;  the  amount  of  nitrogen  may  thus 
be  calcvilated.  If,  for  instance,  an  acid  be  prepared,  containing  20  grains 
of  pure  hydrated  sulphuric  acid  (SOgjHO)  in  1,000  grain-measures  —  200 
grain-measures  of  this  acid  —  the  quantity  introduced  into  the  bulbs — cor- 
respond to  1-38  grains  of  ammonia,  or  1-14  grains  of  nitrogen.  The  alka- 
line solution  is  so  graduated  that  1,000  grain-measures  will  exactly  neutra- 
lize the  200  grain-measures  of  the  standard  acid.  If  we  now  find  that  the 
acid  partly  saturated  with  the  ammonia,  disengaged  during  the  combustion 
of  a  nitrogenous  substance,  requires  only  700  grain-measures  of  the  alkaline 

200  X  300 
solution,  it  is  evident  that  — —^- —  =  60  grain-measures  were  saturated 

by  the  ammonia,  and  the  quantity  of  nitrogen  is  obtained  by  the  proportion 

1-14  X  60 
200  :  1-14  =  60  :  a;,  wherefrom  z  =  — —- —  =  0-342  grains  of  nitrogen. 

Estimation  of  Sulphur  in  organic  compounds. — When  bodies  of  this  class 
containing  sulphur  are  burned  with  protoxide  of  copper,  a  small  tube  con- 
taining binoxide  of  lead  must  be  interposed  between  the  chloride  of  calcium 
tube  and  the  potass-apparatus  to  retain  any  sulphurous  acid  which  may  be 
formed.  It  is  better,  however,  to  use  chromate  of  lead  in  such  cases.  The 
proportion  of  sulphur  is  determined  by  oxidizing  a  known  weight  of  the  sub- 
stance by  strong  nitric  acid,  or  by  fusion  in  a  silver  vessel  with  ten  or  twelve 
times  its  weight  of  pure  hydrate  of  potassa  and  half  as  much  nitre.  The 
sulphur  is  thus  converted  into  sulphuric  acid,  the  quantity  of  which  can  be 
determined  by  dissolving  the  fused  mass  in  water,  acidulating  with  nitric 
acid,  and  adding  a  salt  of  baryta.  Phosphorus  is,  in  like  manner,  oxidized 
to  phosphoric  acid,  the  quantity  of  which  is  determined  by  precipitation  in 
combination  with  sesquioxide  of  iron,  or  otherwise. 

Estimation  of  Chlorine. — The  case  of  a  volatile  liquid  containing  chlorine 
is  of  most  frequent  occurrence,  and  may  be  taken  as  an  illustration  of  the 
general  plan  of  proceeding.  The  combustion  with  protoxide  of  copper 
must  be  very  carefully  conducted,  and  two  or  three  inches  of  the  anterior 
portion  of  the  tube  kept  cool  enough  to  prevent  volatilization  of  the  chloride 
of  copper  into  the  chloride  of  calcium  tube.  Chromate  of  lead  is  much 
better  for  the  purpose.  The  chlorine  is  correctly  determined  by  placing  a 
small  weighed  bulb  of  liquid  in  a  combustion-tube,  which  is  afterwards 


EMPIRICAL    AND    RATIONAL     FORMULA.  329 

filled  witli  fragments  of  pure  quick-lime.  The  lime  is  iDrought  to  a  red- 
heat,  and  the  vapour  of  the  liquid  driven  over  it,  -when  the  chlorine  dis- 
places oxygen  from  the  lime,  and  gives  rise  to  chloride  of  calcium.  When 
cold,  the  contents  of  the  tube  are  dissolved  in  the  dilute  nitric  acid,  filtered, 
and  the  chlorine  precipitated  by  nitrate  of  silver. 

EMPIBICAL   AND   KATIONAL   FOBMUL^. 

A  chemical  formula  is  termed  empirical  when  it  merely  gives  the  simplest 
possible  expression  of  the  composition  of  the  substance  to  which  it  refers. 
A  rational  formula,  on  the  contrary,  aims  at  describing  the  exact  composition 
of  one  equivalent,  or  combining  proportion  of  the  substance,  by  stating  the 
absolute  number  of  equivalents  of  each  of  its  elements  essential  to  that 
object,  as  well  as  the  mere  relations  existing  between  them.  The  empirical 
formula  is  at  once  deduced  from  the  analysis  of  the  substance,  reckoned  to 
100  parts ;  the  rational  requires  in  addition  a  knowledge  of  its  combining 
quantity,  which  can  only  be  obtained  by  direct  experiment,  by  synthesis,  or 
by  the  careful  examination  of  one  or  more  of  its  most  definite  compounds. 
Farther,  the  rational  may  either  coincide  with  the  empirical  formula,  or  it 
may  be  a  multiple  of  the  latter. 

Thus,  the  composition  of  acetic  acid  is  expressed  by  the  formula  C4H3O3, 
which  exhibits  the  simplest  relations  of  the  three  elements,  and  at  the  same 
time  expresses  the  quantities  of  these,  in  equivalents,  required  to  make  up 
an  equivalent  of  acetic  acid ;  hence,  it  is  both  empirical  and  rational.  On 
the  other  hand,  the  empirical  formula  of  crystallized  kinic  acid  is  C^HgOg, 
while  its  rational  formula,  determined  by  its  capacity  of  saturation,  is  double, 
or  CJ4H12O12,  otherwise  written  C(4Hj,0jj,H0.  In  like  manner,  the  empi- 
rical formula  of  the  artificial  alkaloids /wr/wn/je  and  amarine  are  respectively 
CigHgNOg  and  CajHgN.  The  equivalents  of  these  substances,  that  is  to  say, 
the  quantities  required  to  form  neutral  salts  with  one  equivalent  of  any  well- 
defined  monobasic  acid,  will,  however,  be  expressed  by  the  formulae  CgjHjj 
N20g  and  C^gHjgNj ;  hence  these  latter  deserve  the  name  of  rational. 

The  deduction  of  an  empirical  formula  from  the  ultimate  analysis  is  very 
easy ;  the  case  of  sugar,  already  cited,  may  be  taken  as  an  example.  This 
contains,  according  to  the  analysis,  in  100  parts 

Carbon 41-98 

Hydrogen 6-43 

Oxygen 51-59 

100^ 

If  each  of  these  quantities  be  divided  by  the  equivalent  of  the  element, 
the  quotients  will  express  in  equivalents  the  relations  existing  between  them  ; 
these  are  afterwards  reduced  to  their  simplest  expression.  This  is  the  only 
part  of  the  calculation  attended  with  any  difficulty ;  if  the  numbers  were  rigidly 
correct,  it  would  only  be  necessary  to  divide  each  by  the  greatest  divisor 
common  to  the  whole ;  as  they  are,  however,  only  approximative,  something 
is  of  necessity  left  to  the  judgment  of  the  experimenter,  who  is  obliged  to 
use  more  indirect  means. 

41-98  51-59 

— g— =6-99;  6-43;  -g— =6-44, 

or  699  eq.  carbon,  643  eq.  hydrogen,  and  644  eq.  oxygen. 
It  will  be  evident,  in  the  first  place,  that  the  hydrogen  and  oxygen  are 
present  in  the  proportions  to  form  water,  or  as  many  equivalents  of  one  as 
»f  the  other.     Again,  the  equivalents  of  carbon  and  hydrogen  are  nearly  in 
28  * 


330 


DETERMINATION   OP  TH*  DENSITY  OP  VAPOURS. 


the  proportion  of  12 :  11,  so  that  the  formula  CjgHjiOjj  appears  likely  to  be 
correct.  It  is  now  easy  to  see  how  far  this  is  admissible,  by  reckoning  it 
back  to  100  parts,  comparing  the  result  with  the  numbers  given  by  the  actual 
analysis,  and  observing  whether  the  diflFerence  falls  fairly  in  direction  and 
amount  within  the  limits  of  error  of  what  may  be  termed  a  good  experiment, 
viz.,  two  or  three-tenths  per  cent,  deficiency  in  the  carbon,  and  not  more  than 
one-tenth  per  cent,  excess  in  the  hydrogen. 

Carbon 6x12=72 

Hydrogen 11  eq.  =  ll 

Oxygen... 8x11=88 


171  :  72=100  :  42-11 
171  :  11  =  100  :  6-43 
171  :  88=100  :  51-46 


171 


Organic  acids  and  salt-radicals  have  their  proper  equivalents  most  fre- 
quently determined  by  an  analysis  of  their  lead-  and  silver-salts,  by  burning 
these  latter  with  suitable  precautions  in  a  thin  porcelain  capsule,  and  noting 
the  weight  of  the  protoxide  of  lead  or  metallic  silver  left  behind.  If  the 
protoxide  of  lead  be  mixed  with  globules  of  reduced  metal,  the  quantity  of 
the  latter  must  be  ascertained  by  dissolving  away  the  oxide  by  acetic  acid. 
Or  the  lead-salt  may  be  converted  into  sulphate,  and  the  silver-compound 
into  chloride,  and  both  metals  thus  estimated.  An  organic  base,  on  the  con- 
trary, or  a  basyle,  has  its  equivalent  fixed  by  the  observation  of  the  quantity 
of  a  mineral  acid,  or  an  inorganic  salt-radical,  required  to  form  with  it  a 
combination  having  the  characters  of  neutrality. 

DETERMINATION  OF  THE  DENSITY  OF  VAPOUES. 

The  determination  of  the  specific  gravity  of  the  vapour  of  a  volatile  sub- 
stance is  frequently  a  point  of  great  importance,  inasmuch 
Fig.  164.  as  it  gives  the  means,  in  conjunction  with  the  analysis,  of 

representing  the  constitution  of  the  substance  by  measure 
in  a  gaseous  state.  The  following  is  a  sketch  of  the  plan 
of  operation  usually  followed  :  —  A  light  glass  globe,  fig. 
164,  about  three  inches  in  diameter,  is  taken,  and  its  neck 
softened  and  drawn  out  in  the  blowpipe-flame,  as  repre- 
sented in  the  figure,  this  is  accurately  weighed.  About 
one  hundred  grains  of  the  volatile  liquid  are  then  intro- 
duced, by  gently  warming  the  globe  and  dipping  the  point 
into  the  liquid,  which  is  then  forced  upwards  by  the  pres- 
sure of  the  air  as  the  vessel  cools.  The  globe  is  next 
firmly  attached  by  wire  to  a  handle,  in  such  a  manner  that 
it  may  be  plunged  into  a  bath  of  boiling  water  or  heated 
oil,  and  steadily  held  with  the  point  projecting  upwards. 
The  bath  must  have  a  temperature  considerably  above 
that  of  the  boiling-point  of  the  liquid.  The  latter  becomes 
rapidly  converted  into  vapour,  which  escapes  by  the  nar- 
row orifice,  chasing  before  it  the  air  of  the  globe.  When 
the  issue  of  vapour  has  wholly  ceased,  and  the  temperature  of  the  bath,  care- 
fully observed,  appears  pretty  uniform,  the  open  extremity  of  the  point  is 
hermetically  sealed  by  a  small  blowpipe-flame.  The  globe  is  removed  from 
the  bath,  suffered  to  cool,  cleansed  if  necessary,  and  weighed,  after  which 
the  neck  is  broken  off  beneath  the  surface  of  water  which  has  been  boiled 
and  cooled  out  of  contact  of  air,  or  better,  mercury.  The  liquid  enters  the 
globe,  and,  if  the  expulsion  of  the  air  by  the  vapour  has  been  complete,  filla 


DETERMINATION  OP  THE  DENSITY  OP  VAPOURS.    331 

it ;  if  otherwise,  an  air-bubble  is  left,  whose  volume  can  be  easily  ascertained 
by  pouring  the  liquid  from  the  globe  into  a  jar  graduated  to  cubic  inches, 
and  then  re-filling  the  globe,  and  repeating  the  same  observation.  Thf 
capacity  of  the  vessel  is  thus  at  the  same  time  known ;  and  these  are  all  thd 
data  required.     An  example  will  render  the  whole  intelligible. 

Determination  of  the  density  of  the  vapour  of  Acetone. 

Capacity  of  globe 31-61  cubic  inches 

Weight  of  globe  filled  with  dry  air  at  52°  (11°-11C) 

and  30-24  inches  barometer 2070-88  grains. 

Weight  of  globe  filled  with  vapour  at  212°  (100°C) 

temp,  of  the  bath  at  the  moment  of  sealing  the 

point,  and  30-24  inches  barometer 2076-81  grains. 

Residual  air,  at  45°  (7° -220,  and  30-24  inches 

barometer 0-60  cubic  inch. 


31-61  cub.  inches  of  air  at  52°  and  30-24  in  bar. =32-36  cub.  inches  at  60<» 

(15°-C)  and  30  inch,  bar.,  weighing 10-035  grains. 

Hence,  weight  of  empty  globe 2070-88—10-035=2060-845  grains. 


0-6  c.  inch  of  air  at  45°=:0-8  c.  inch  at  212°  ;  weight  of  do.  by  calculation 

=0-191  grain. 
31-61—0-8  =  30-81  cubic  inches  of  vapour  at  212°  and  30-24  in.  bar.,  which, 

on  the  supposition  that  it  could  hear  cooling  to  60°  without  liquefaction,  would, 

at  that  temperature,  and  under  a  pressure  of  30  inch,  bar.,  become  reduced 

to  24-18  cubic  inches. 
Hence, 

Weight  of  globe  and  vapour 2076-810  grains. 

,,  residual  air 0-191 

2076-619 
Weight  of  globe 2060-845 

Weight  of  the  24-18  cubic  inches  of  vapour 15-774 

Consequently,  100  cubic  inches  of  such  vapour  must 

weigh,. 65-23 

100  cubic  inches  of  air,  under  similar  circumstances, 

weigh 31-01 

65-23 

■  =2-103,  the  specific  gravity  of  the  vapour  in  question,  an 
"1*"1     being  unity. 


_  In  the  foregoing  statement  a  correction  has  been,  for  the  sake  of  simpli 
city,  omitted,  which,  in  very  exact  experiments,  must  not  be  lost  sight  of 
viz.,  the  expansion  and  change  of  capacity  of  the  glass  globe  by  the  elevated 
temperature  of  the  bath.  The  density  so  obtained  will  be  always  en  this 
account  a  little  too  high. 

The  error  to  which  the  mercurial  thermometer  is,  at  high  temperatures, 
liable,  tends  in  the  opposite  direction. 


J32  DETERMINATION   OF   THE   DENSITY   OF    VAPOURS. 

It  is  easy  to  compare  the  actual  specific  gravity  of  the  vapour  found  in  the 
manner  above  described  with  the  theoretical  specific  gravity  deduced  from  the 
formula  of  the  substance: — 

The  formula  of  acetone  is  CjHgO.  In  combining  volumes  this  is  repre- 
sented by  3  vols,  of  the  hypothetical  vapour  of  carbon,  3  vols,  of  hydrogen, 
and  half  a  volume  of  oxygen.  Or  the  weight  of  the  unit  of  volume  of  ace- 
tone-vapour will  be  equal  to  three  times  the  specific  gravity  of  carbon-va- 
pour, three  times  that  of  hydrogen,  and  one-half  that  of  oxygen  added 
together,  one  volume  of  the  compound  vapour  containing  6^  volumes  of  its 
components : 

3  vols,  hypothetical  vapour  of  carbon 0-4183  x  3=1-2549 

3  vols,  hydrogen 0-0693x3=0-2079 

J  vol.  oxygen =0-5528 

Theoretical  specific  gravity 2-0156 


CANE    AND    GRAPE-SUGAE.  833 


SECTION  I. 

NON-AZOTIZED  BODIES  OF  THE  SACCHARINE  AND  AMYLACEOUS 

GROUP. 


SUaAR,    STARCH,    GUM,    LIGNIN,    AND   ALLIED    SUBSTANCES. 

The  members  of  this  remarkable  and  very  natural  group  present  several 
interesting  cases  of  isomerism.  They  are  characterized  by  their  feeble 
aptitude  to  enter  into  combination,  and  also  by  containing,  with  perhaps  one 
exception,  oxygen  and  hydrogen  in  the  proportions  to  form  water. 

Table  of  Saccharine  and  Amylaceous  Substances. 

Cane-sugar,  crystallized C24H22O22 

Cane-sugar,  in  combination 024H,gO,g 

Grape-sugar,  crystallized C24H2802g 

Grape-sugar,  in  combination 024H2i02i 

Milk-sugar,  crystallized  C24H24O24 

Milk-sugar,  in  combination ^^fin^i^ 

Sugar  from  Secale  cornutum 024H2gO26 

Mannite Cg  H^  Og 

Starch,  unaltered,  dried  at  212°  (lOOoC) C24H20O20 

Amidin,  or  gelatinous  starch OjjiHgoOgo 

Dextrin,  or  gummy  starch O24H2QO20 

Starch  from  Cetraria  Islandica O24H20O20 

Inulin O24H21O21 

Gum- Arabic C24H22O22 

Gum-tragacanth O24H20O20 

Lignin,  or  cellulose O24H20O20 

Cane-sugar  ;  ordinary  sugar,  C24H22O22. — This  most  useful  substance  is 
found  in  the  juice  of  many  of  the  grasses,  in  the  sap  of  several  forest-trees, 
in  the  root  of  the  beet  and  the  mallow,  and  in  several  other  plants.  It  is 
extracted  most  easily  and  in  greatest  abundance  from  the  sugar-cane,  culti- 
vated for  the  purpose  in  many  tropical  countries.  The  canes  are  crushed 
between  rollers,  and  the  expressed  juice  suffered  to  flow  into  a  large  vessel 
where  it  is  slowly  heated  nearly  to  its  boiling-point.  A  small  quantity  of 
hydrate  of  lime  mixed  with  water  is  then  added,  which  occasions  the  separa- 
tion of  a  coagulum  consisting'chiefly  of  earthy  phosphates,  waxy  matter,  a 
peculiar  albuminous  principle,  and  mechanical  impurities.  The  clear  liquid 
separated  from  the  coagulum  thus  produced  is  rapidly  evaporated  in  open 
pans  heated  by  a  fierce  fire  made  with  the  crushed  canes  of  the  preceding 
year,  dried  in  the  sun  and  preserved  for  the  purpose.  When  sufficiently 
concentrated  the  syrup  is  transferred  to  a  shallow  vessel,  and  left  to  crys- 
tallize, during-  which  time  it  is  frequently  agitated  in  order  to  hasten  the 
change  and  hinder  the  formation  of  large  crystals.     It  is,  lastly,  drained 


834  CANE    AND    GRAPE-SUGAR. 

from  the  dark  uncrystallizable  syrup,  or  molasses,  and  sent  into  commerce, 
under  the  name  of  rato  or  Muscovado  sugar.  The  refining  of  this  crude  pro- 
duct is  effected  by  re-dissolving  it  in  water,  adding  a  quantity  of  albumen  in 
the  shape  of  serum  of  blood  or  white  of  egg,  and  sometimes  a  little  lime- 
water,  and  heating  the  whole  to  the  boiling-point ;  the  albumen  coagulates, 
and  forms  a  kind  of  net-work  of  fibres,  which  inclose  and  separate  from  the 
liquid  all  mechanically  suspended  impurities.  The  solution  is  decolorized  by 
filtration  through  animal  charcoal,  evaporated  to  the  crystallizing-point,  and 
put  into  conical  earthen  moulds,  wheie  it  solidifies,  after  some  time,  to  a 
confusedly-crystalline  mass,  which  is  drained,  washed  with  a  little  clean 
syrup,  and  dried  in  a  stove ;  the  product  is  ordinary  loaf-sugar.  When  the 
crystallization  is  allowed  to  take  place  quietly  and  slowly,  sugar-candy  re- 
sults, the  crystals  under  these  circumstances  acquiring  large  volume  and 
regular  form.  The  evaporation  of  the  decolorized  syrup  is  best  conducted 
in  strong  close  boilers  exhausted  of  air ;  the  boiling-point  of  the  syrup  is 
reduced  in  consequence  from  230°  (110°C)  to  150°  (65°-5C)  or  below,  and 
and  the  injurious  action  of  the  heat  upon  the  sugar  in  great  measure  pre- 
vented. Indeed,  the  production  of  molasses  in  the  rude  colonial  manufacture 
is  chiefly  the  result  of  the  high  and  long-continued  heat  applied  to  the  cane- 
juice,  and  might  be  almost  entirely  prevented  by  the  use  of  vacuum-pans, 
the  product  of  sugar  being  thereby  greatly  increased  in  quantity,  and  so  far 
improved  in  quality  as  to  become  almost  equal  to  the  refined  article. 

In  liiany  parts  of  the  continent  of  Europe  sugar  is  manufactured  on  a  large 
scale  from  beet-root,  which  contains  about  8  per  cent,  of  that  substance.  The 
process  is  far  more  complicated  and  troublesome  than  that  just  described, 
and  the  product  much  inferior.  When  refined,  however,  it  is  scarcely  to  be 
distinguished  from  the  preceding.  The  inhabitants  of  the  Western  States  of 
America  prepare  sugar  in  considerable  quantity  from  the  sap  of  the  sugar- 
maple,  Acer  saccharinum,  which  is  common  in  those  parts.  The  tree  is  tapped 
in  the  spring  by  boring  a  hole  a  little  way  into  the  wood,  and  inserting  a 
small  spout  to  convey  the  liquid  into  a  vessel  placed  for  its  reception.  This 
is  boiled  down  in  an  iron  pot,  and  furnishes  a  coarse  sugar,  which  is  almost 
wholly  employed  for  domestic  purposes,  but  little  finding  its  way  into  com^ 
merce. 

Pure  sugar  slowly  separates  from  a  strong  solution  in  large,  transparent 
colourless  crystals,  having  the  figure  of  a  modified  oblique  rhombic  prism. 
It  has  a  pure,  sweet  taste,  is  very  soluble  in  water,  requiring  for  solution 
only  one-third  of  its  weight  in  the  cold,  and  is  also  dissolved  by  alcohol,  but 
with  more  difficulty.  When  moderately  heated  it  melts,  and  solidifies  on 
cooling  to  a  glassy  amorphous  mass,  familiar  under  the  name  of  barley  sugar: 
at  a  higher  temperature  it  blackens  and  suffers  decomposition ;  and  the  same 
effect  is  produced,  as  already  remarked,  by  long-continued  boiling  of  the 
aqueous  solution,  which  loses  its  faculty  of  crystallizing  and  acquires  colour. 
The  crystals  have  a  specific  gravity  of  1*6,  and  are  unchanged  in  the  air. 

The  deep  brown  soluble  substance  called  caramel,  used  for  colouring  spirits, 
and  other  purposes,  is  a  product  of  the  action  of  heat  upon  cane-sugar.  It 
contains  C24H18O18,  and  is  isomeric  with  cane-sugar  in  combination. 

The  following  is  the  composition  assigned  to  the  principal  compounds  of 
cane-sugar  by  M.  P^ligot,  who  has  devoted  much  attention  to  the  subject.' 

Crystallized  cane-sugar C24ll,80,8-f  4H0 

Compound  of  sugar  with  common  salt CjiHigOjg-i-NaCl-j-SHO 

Compound  of  sugar  with  baryta C24Hj80,g-j-2BaO-f-4HO 

Compound  of  sugar  with  lime C24HigO,g-j-2CaO-|-4HO 

(Compound  of  sugar  with  protoxide  of  lead  ....  C24H,gOig-f-4PbO 

»  Ann.  Chim.  et  Phys.  Ixrii.  113. 


CANE    AND    GRAPE-SUGAR.  335 

The  compounds  with  baryta  and  lime  are  prepared  by  digesting  sugar  at 
a  gentle  heat  with  the  hydrates  of  the  earths.  The  lime-compound  has  a 
bitter  taste,  and  is  more  soluble  in  cold  water  than  in  hot.  Both  are  readily 
decomposed  by  carbonic  acid,  crystals  of  carbonate  of  lime  being  occasion- 
ally produced.  The  combination  with  protoxide  of  lead  is  prepared  by  mix- 
ing sugar  with  a  solution  of  acetate  of  lead,  adding  excess  of  ammonia,  and 
drying  the  white  insoluble  product  out  of  contact  with  air.  The  compound 
with  common  salt  is  crystallizable,  soluble,  and  deliquescent. 

Gkapb-sugar  ;  glucose  ;  sugar  of  fruits,  C24H28O28.  —  This  variety  of 
ugar  is  very  abundantly  diffused  through  the  vegetable  kingdom  ;  it  may  be 
extracted  in  large  quantity  from  the  juice  of  sweet  grapes,  and  also  from 
honey,  of  which  it  forms  the  solid  crystalline  portion,  by  washing  with  cold 
alcohol,  which  dissolves  the  fluid  syrup.  It  may  also  be  prepared  by  arti- 
ficially modifying  cane-sugar,  starch,  and  woody  fibre,  by  processes  presently 
to  be  described.  The  appearance  of  this  substance,  to  an  enormous  extent, 
in  the  urine,  is  the  most  characteristic  feature  of  the  disease  called  diabetes. 

Grape-sugar  is  easily  distinguished  by  several  important  peculiarities  from 
cane-sugar:  it  is  much  less  sweet,  and  less  soluble  in  water,  requiring  IJ 
parts  of  the  cold  liquid  for  solution.  Its  mode  of  crystallization  is  also 
completely  different ;  instead  of  forming,  like  cane-sugar,  bold,  distinct  crys- 
tals, it  separates  from  its  solutions  in  water  and  alcohol  in  granular  warty 
masses,  which  but  seldom  present  crystalline  faces.  When  pure,  it  is  nearly 
white.  When  heated,  it  melts,  and  loses  4  eq.  of  water,  and  at  a  higher 
temperature  blackens  and  suffers  decomposition.  Grape-sugar  combines 
with  difficulty  with  lime,  baryta,  and  oxide  of  lead,  and  is  converted  into  a 
brown  or  black  substance  when  boiled  with  solution  of  caustic  alkali,  by 
which  cane-sugar  is  but  little  affected.  It  dissolves,  on  the  contrary,  in 
strong  oil  of  vitriol  without  blackening,  and  gives  rise  to  a  peculiar  com- 
pound acid,  whose  baryta-salt  is  soluble.  Cane-sugar  is,  under  these  cir- 
cumstances, instantly  changed  to  a  black  mass  resembling  charcoal. 

AVhen  solutions  o'f  cane  and  grape-sugar  are  mixed  with  two  separate  por- 
tions of  solution  of  sulphate  of  copper,  and  caustic  potassa  added  in  excess 
to  each,  deep  blue  liquids  are  obtained,  which,  on  being  heated,  exhibit  dif- 
ferent characters ;  the  one  containing  cane-sugar  is  at  first  but  little  altered  ; 
a  small  quantity  of  red  powder  falls  after  a  time,  but  the  liquid  long  retains 
its  blue  tint :  with  the  grape-sugar,  on  the  other  hand,  the  first  application 
of  heat  throws  down  a  copious  greenish  precipitate,  which  rapidly  changes 
to  scarlet,  and  eventually  to  dark  red,  leaving  a  nearly  colourless  solution. 
This  is  an  excellent  test  for  distinguishing  the  two  varieties  of  sugar,  or  dis- 
covering an  admixture  of  grape  with  cane-sugar. 

Grape-sugar  unites  with  common  salt,  forming  a  soluble  compound  of 
sweetish  saline  taste,  which  crystallizes  in  a  regular  and  beautiful  manner. 

Compounds  of  Grape-sugar,  according  to  Peligot. 

Crystalline  grape-sugar  dried  in  the  air C24H2i02i  +  7HO 

The  same,  dried  at  266°  (130°C)  C24H2i02i-|-3HO 

Compound  of  grape-sugar  with  common  salt C24H2i02i-f  NaCl-f  5H0 

The  same,  dried  at  266°  (130°C) C24H2i02i-fNaCl-f  2H0 

Compound  of  grape-sugar  with  baryta C24H2i02i-|--3BaO-f  7H0 

Compound  of  grape-sugar  with  Ume  CgiHgAi-f  ^CaO-f  7H0 

Compound  of  grape-sugar  with  protoxide  of  lead  C24H2i02i-}-6PbO 

Sulphosaccharic  Acid,  C24H2o02p,S03.  —  Melted  grape-sugar  is  cautiously 
mixed  with  concentrated  sulphuric  acid,  the  product  dissolved  in  water,  and 
neutralized  with  carbonate  of  baryta ;  sulphate  of  baryta  is  formed  together 
with  a  soluble  sulphosaccharate  of  that  earth,  from  which  the  acid  itself 


336  CANE    AND    GRAPE-SUGAR. 

may  be  afterwards  eliminated.  It  is  a  sweetish  liquid,  forming  a  variety  of 
Boluble  salts,  and  very  prone  to  decompose  into  sugar  and  sulphuric  acid. 

Action  of  dilute  Acids  upon  Sugar. — Cane-sugar  dissolved  in  dilute  sulphuric 
acid  is  gradually  but  completely  converted,  at  the  common  temperature  of 
the  air,  into  grape-sugar.  The  same  solution,  when  long  boiled,  yields  a 
brownish-blaok  and  nearly  insoluble  substance,  which  is  a  mixture  of  two 
distinct  bodies,  one  having  the  appearance  of  small  shining  scales,  and  the 
other  that  of  a  dull  brown  powder.  The  first,  called  by  Boullay  and  Mala- 
guti  MZmm,  and  by  Liebig  sacchulmin,  is  insoluble  in  ammonia  and  alkalis; 
the  second,  ulmic  acid,  the  sacchulmic  acid  of  Liebig,  dissolves  freely,  yielding 
dark  brown  solutions  precipitable  by  acids.  By  long-continued  boiling  with 
water,  sacchulmic  acid  is  converted  into  sacchulmin.  Both  these  substances 
have  the  same  composition,  expressed  by  the  empirical  formula  CjHO.  Hy- 
drochloric acid  in  a  dilute  state,  produces  the  same  eflFects.* 

Action  of  Alkalis  upon  Sugar. — When  lime  or  bf^ryta  is  dissolved  in  a  solu- 
tion of  grape-sugar,  and  the  whole  left  to  itself  several  weeks  in  a  close 
vessel,  the  alkaline  reaction  will  be  found  to  have  disappeared  from  the  for- 
mation of  an  acid  substance.  By  mixing  this  solution  with  basic  acetate  of 
lead,  a  voluminous  white  precipitate  is  obtained,  which,  when  decomposed 
by  sulphuretted  hydrogen,  yields  sulphide  of  lead,  and  the  new  acid,  to  which 
the  term  kalisaccharic  or  glucic  is  applied.  Glucic  acid  is  very  soluble  and 
deliquescent,  has  a  sour  taste  and  acid  reaction :  its  salts,  with  the  exception 
of  that  containing  protoxide  of  lead,  are  very  soluble.  It  contains  CgHgOg. 
When  grape-sugar  is  heated  in  a  strong  solution  of  potassa,  soda,  or  baryta, 
the  liquid  darkens,  and  at  length  assumes  a  nearly  black  colour.  The  addi- 
tion of  an  acid  then  gives  rise  to  a  black  fiocculent  precipitate  of  a  substance 
called  melasinic  acid,  containing  C24Hj20,o.  Cane-sugar  long-boiled  with 
alkalis  undergoes  the  same  changes,  being  probably  first  converted  into 
grape-sugar. 

Sugar  from  ergot  of  bye.  —  This  variety  of  sugar,  extracted  by  alcohol 
from  the  ergot,  crystallizes  in  transparent  colourless  prisms,  which  have  a 
sweet  taste,  and  are  very  soluble  in  water.  It  differs  from  cane-sugar  in  not 
reducing  the  acetate  of  copper  when  boiled  with  a  solution  of  that  substance. 
It  contains  C24H2603g. 

Sugar  of  diabetes  insipidus.  —  A  substance  having  the  other  properties 
of  a  sugar,  but  destitute  of  sweet  taste,  has  been  described  by  M.  Th^nard 
as  having  been  obtained  from  the  above-mentioned  source.  It  was  capable 
of  furnishing  alcohol  by  fermentation,  and  of  suflFering  conversion  into  grape- 
sugar  by  dilute  sulphuric  acid.     Its  composition  is  unknown. 

LiQUORiCE-suGAR ;  GLYCYRRHiziN.  —  The  root  of  the  common  liquorice 
yields  a  large  quantity  of  a  peculiar  sweet  substance,  which  is  soluble  in 
water,  but  refuses  to  crystallize ;  it  is  remarkable  for  forming  with  acids 
compounds  which  have  but  sparing  solubility.  Glycyrrhizin  cannot  be  made 
to  ferment.     The  formula  of  this  substance  is  not  definitely  settled. 

Sugar  of  milk;  lactin,  C24H24O2J.— This  curious  substance  is  an  impor- 
tant constituent  of  milk ;  it  is  obtained  in  large  quantities  by  evaporating 
whey  to  a  syrupy  state,  and  purifying  the  lactin,  which  slowly  crystallizes  out 
by  animal  charcoal.    It  forms  white,  translucent,  four-sided  prisms,  of  great 

'  Under  the  names  ulmin  and  vlmic  acid  (humin  and  Mimic  acid,  crenic  and  a^o-crenic  acids,) 
have  been  confounded  a  number  of  brown  or  black  uncrystallizable  substances,  produced  by  the 
action  of  powerful  chemical  agents  upon  sugar,  lignin,  &c.,  or  generated  by  the  putrefactive 
d9cay  of  vegetable  fibre.  Common  garden  mould,  for  example,  treated  with  dilute,  boi^ng 
polution  of  caustic  potassa,  vields  a  deep  brown  solution,  from  which  acids  precipitate  a  floo- 
culent,  brown  substance,  having  but  a  slight  degree  of  solubility  in  water.  This  is  generally 
jiilled  tdmic  or  humic  acid,  and  its  origin  ascribed  to  the  reaction  of  the  alkali  on  the  ulmin 
or  hvmus  of  the  soil.  It  is  known  that  these  iKxiies  differ  exceedingly  in  composition;  th^ 
«r«>  Uw  itt<l»t&ajto  *so  ada)i>^  of  ready  investigation. 


MANNITE— STARCH.  337 

hardness.  It  is  slow  and  diflBcult  of  solution  in  cold  water,  requiring  for 
that  purpose  5  or  6  times  its  weight ;  it  has  a  feeble  sweet  taste,  and  in  the 
solid  state  feels  gritty  between  the  teeth.  When  heated,  it  loses  water,  and  at 
a  high  temperature  blackens  and  decomposes.  Milk-sugar  forms  several  com- 
pounds with  protoxide  of  lead,  and  is  converted  into  grape-sugar  by  boiling 
with  dilute  mineral  acids.  It  is  not  directly  fermentable,  but  can  be  made, 
under  particular  circumstances,  to  furnish  alcohol. 

Manna-sugar  ;  mannitb,  C6H7O8  or  CjjHj^Oij.  —  This  is  the  chief  compo- 
nent of  manna,  an  exudation  from  a  species  of  ash ;  it  is  also  found  in  the 
juice  of  certain  other  plants,  and  in  several  sea-weeds,  and  may  be  formed 
artificially  from  ordinary  sugar  by  a  peculiar  kind  of  fermentation.  It  is 
best  prepared  by  treating  manna  with  boiling  alcohol,  and  filtering  the  solu- 
tion whilst  hot ;  the  mannite  crystallizes  on  cooling  in  tufts  of  slender  colour- 
less needles.  It  is  fusible  by  heat  without  loss  of  weight,  is  freely  soluble 
in  water,  possesses  a  powerfully  sweet  taste,  and  has  no  purgative  properties. 
Mannite  refuses  to  ferment.  This  substance  combines  with  sulphuric  acid, 
giving  rise  to  a  new  acid,  the  composition  of  which  is  not  yet  definitely 
established.  It  is  likewise  acted  on  by  concentrated  nitric  acid.  The  product 
of  this  action  will  be  noticed  farther  on.  The  substance  formerly  described 
as  mushroom-sugar  is  merely  mannite. 

Starch  ;  fecula.  —  This  is  one  of  the  most  important  and  widely  diffused 
of  the  vegetable  proximate  principles,  being  found  to  a  greater  or  less  extent 
in  every  plant.  It  is  most  abundant  in  certain  roots  and  tubers,  and  in  soft 
stems:  seeds  often  contain  it  in  large  quantity.  From  these  sources  the 
fecula  can  be  obtained  by  rasping  or  grinding  to  pulp  the  vegetable  structure, 
and  washing  the  mass  upon  a  sieve,  by  which  the  torn  cellular  tissue  is  re- 
tained, while  the  starch  passes  through  with  the  liquid,  and  eventually  settles 
down  from  the  latter  as  a  soft,  white,  insoluble  powder,  which  may  be  washed 
with  cold  water,  and  dried  with  very  gentle  heat.  Potatoes  treated  in  this 
manner  yield  a  large  proportion  of  starch.  Starch  from  grain  may  be  pre- 
pared in  the  same  manner,  by  mixing  the  meal  with  water  to  a  paste,  and 
washing  the  mass  upon  a  sieve :  a  nearly  white,  insoluble  substance  called 
gluten  or  glutin  remains  behind,  which  contains  a  large  proportion  of  nitrogen. 
The  glutin  of  wheat-flour  is  extremely  tenacious  and  elastic.  The  value  of 
meal  as  an  article  of  food  greatly  depends  upon  this  substance.  Starch  from 
grain  is  commonly  manufactured  on  the  large  scale  by  steeping  the  material 
in  water  for  a  considerable  period,  when  the  lactic  acid,  always  developed 
under  such  circumstances  from  the  sugar  of  the  seed,  disintegrates,  and  in 
part  dissolves  the  azotized  matter,  and  greatly  facilitates  the  mechanical 
separation  of  that  which  remains.  A  still  more  easy  and  successful  process 
has  lately  been  introduced,  in  which  a  very  dilute  solution  of  caustic  soda, 
containing  about  200  grains  of  alkali  to  a  gallon  of  liquid  is  employed  with 
the  same  view.  Excellent  starch  is  thus  prepared  from  rice.  Starch  is  inso- 
luble in  cold  water,  as  indeed  its  mode  of  preparation  sufficiently  shows  ;  it 
is  equally  insoluble  in  alcohol  and  other  liquids  which  do  not  effect  its  de- 
composition. To  the  naked  eye  it  presents  the  appearance  of  a  soft,  white, 
and  often  glistening  powder ;  under  the  microscope  it  is  seen  to  be  altogether 
destitute  of  crystalline  structure,  but  to  possess,  on  the  contrary,  a  kind  of 
organization,  being  made  up  of  multitudes  of  little  rounded  transparent 
bodies,  upon  each  of  which  a  series  of  depressed  parallel  rings  surrounding 
a  central  spot  or  hilum,  may  often  be  traced.  The  starch-granules  from  dif- 
ferent plants  vary  both  in  magnitude  and  form  ;  those  from  the  Canna  coc- 
cinea,  or  tons  les  mois,  and  potato  being  largest :  and  those  from  wheat,  and 
the  cereals  in  general,  very  much  smaller.  The  figure  on  the  next  page 
(Fig.  165)  will  sei  ve  to  convey  an  idea  of  the  appearance  of  the  granules  gf 
potato-starch,  highly  magnified. 
29 


338 


DEXTRIN. 


Fig.  165.  "When  a  mixture  of  starch  and  water  is  heated 

to  near  the  boiling-point  of  the  latter,  the  granules 
burst  and  disappear,  producing,  if  the  proportion 
of  starch  be  considerable,  a  thick  gelatinous  mass, 
very  slightly  opalescent  from  the  shreds  of  very 
fine  membrane,  the  envelope  of  each  separate 
granule.  By  the  addition  of  a  large  quantity  of 
water,  this  gelatinous  starch,  or  amidin,  may  be 
so  far  diluted  as  to  pass  in  great  measure  through 
filter-paper.  It  is  very  doubtful,  however,  how 
far  the  substance  itself  is  really  soluble  in  water, 
at  least  when  cold ;  it  is  more  likely  to  be  merely 
suspended  in  the  liquid  in  the  form  of  a  swollen, 
transparent,  insoluble  jelly,  of  extreme  tenuity. 
Gelatinous  starch,  exposed  in  a  thin  layer  to  a 
dry  atmosphere,  becomes  converted  into  a  yel- 
lowish, horny  substance,  like  gum,  which,  when 
put  into  water,  again  softens  and  swells. 

Thin  gelatinous  starch  is  precipitated  by  many  of  the  metallic  oxides,  as 
lime,  baryta,  and  protoxide  of  lead,  and  also  by  a  large  addition  of  alcohol. 
Infusion  of  galls  throws  down  a  copious  yelloAvish  precipitate  containing 
tannic  acid,  which  re-dissolves  when  the  solution  is  heated.  By  far  the 
most  characteristic  reaction,  however,  is  that  with  free  iodine,  which  forms 
with  starch  a  deep  indigo-blue  compound,  which  appears  to  dissolve  in  pure 
water,  although  it  is  insoluble  in  solutions  containing  free  acid  or  saline 
matter.  The  blue  liquid  has  its  colours  destroyed  by  heat,  temporarily  if 
the  heat  be  quickly  withdraw,  and  permanently  if  the  boiling  be  long  con- 
tinued, in  which  case  the  compound  is  decomposed  and  the  iodine  volati- 
lized. Starch  in  the  dry  state,  put  into  iodiue-water,  acquires  a  purplish- 
black  colour. 

The  unaltered  and  the  gelatinous  starch,  in  a  dried  state,  have  the  same 
composition,  namely,  (^24^2{P9o'''  ^  compound  of  starch  and  protoxide  of 
lead  was  found  to  contain,  when  dried  at  212°  (100°C),  C^J^^o^^Q-if-^VhO. 

Dextrin. — When  gelatinous  starch  is  boiled  with  a  small  quantity  of 
dilute  sulphuric,  hydrochloric,  or,  indeed,  almost  any  acid,  it  speedily  loses 
its  consistency,  and  becomes  thin  and  limpid,  from  having  suffered  conver- 
sion into  a  soluble  substance,  resembling  gum,  called  dextrin.'  The  experi- 
ment is  most  conveniently  made  with  sulphuric  acid,  which  may  be  after- 
wards withdrawn  by  saturation  with  chalk.  The  liquid  filtered  from  the 
nearly  insoluble  gypsum  may  then  be  evaporated  in  a  water-bath  to  dry- 
ness. The  result  is  a  gum-like  mass,  destitute  of  crystalline  structure, 
soluble  in  cold  water,  and  precipitable  from  its  sohition  by  alcohol,  and 
capable  of  combining  with  protoxide  of  lead. 

When  the  ebullition  with  the  dilute  acid  is  continued  for  a  considerable 
period,  the  dextrin  first  formed  undergoes  a  farther  change,  and  becomes 
converted  into  grape-sugar,  which  can  be  thus  artificially  produced  with  the 
greatest  facility.  The  length  of  time  required  for  this  remarkable  change 
depends  upon  the  quantity  of  acid  present ;  if  the  latter  be  very  small,  it  is 
necessary  to  continue  the  boiling  many  successive  hours,  replacing  the 
water  which  evaporates.  With  a  larger  proportion  of  acid,  the  conversion  is 
much  more  speedy.  A  mixture  of  16  parts  potato-starch,  60  parts  water, 
and  6  parts  sulphuric  acid,  may  be  kept  boiling  for  about  four  hours ;  the 
liquid  neutralized  with  chalk,  filtered,  and  rapidly  evaporated  to  a  small 


*  Fpoio  its  a-tion  en  polarized  light,  twisting  the  plane  of  polarization  towards  the  right 
htaid. 


DEXTRIN  —  STARCH  —  INULIN.  889- 

bulk.  By  digestion  with  animal  charcoal  and  a  second  filtration  much  of 
the  colour  will  be  removed,  after  which  the  solution  may  be  boiled  down  to 
a  thin  syrup  and  left  to  crystallize  ;  in  the  course  of  a  few  days  it  solidifies 
to  a  mass  of  grape-sugar.  There  is  another  method  of  preparing  this  sub- 
stance from  stared  which  deserves  particular  notice.  .Germinating  seeds, 
and  buds  in  the  act  of  development,  are  found  to  contain  a  small  quantity 
of  a  peculiar  azotized  substance,  formed  at  this  particular  period  from  the 
glutin  or  vegetable  albuminous  matter,  to  which  the  name  diastase  is  given. 
This  substance  possesses  the  same  curious  property  of  effecting  the  conver- 
sion of  starch  into  dextrin,  and  ultimately  into  grape-sugar,  and  at  a  much 
lower  temperature  than  that  of  ebullition.  A  little  infusion  of  malt,  or  ger- 
minated barley,  in  tepid  water,  mixed  with  a  large  quantity  of  thick  gela- 
tinous starch,  and  the  whole  maintained  at  160°  (71°C),  or  thereabouts, 
occasions  complete  liquefaction  in  the  space  of  a  few  minutes  from  the  pro- 
duction of  dextrin,  which  in  its  turn  becomes  in  three  or  four  hours  con- 
verted into  sugar.  If  a  greater  degree  of  heat  be  employed,  the  diastase  is 
coagulated  and  rendered  insoluble  and  inactive.  Very  little  is  known 
respecting  diastase  itself;  it  seems  very  much  to  resemble  vegetable  albumin, 
but  has  never  been  got  in  a  state  of  purity. 

The  change  of  starch  or  dextrin  into  sugar,  whether  produced  by  the 
action  of  dilute  acid  or  by  diastase,  takes  place  quite  independently  of  the 
oxygen  of  the  air,  and  is  unaccompanied  by  any  secondary  product.  The 
acid  takes  no  direct  part  in  the  reaction ;  it  may,  if  not  volatile,  be  all  with- 
drawn without  loss  after  the  experiment.  The  whole  affair  lies  between  the 
starch  and  the  elements  of  water ;  a  fixation  of  the  latter  occuring  in  the 
new  product,  as  will  be  seen  at  once  on  comparing  their  composition.  The 
sugar,  in  fact,  so  produced,  very  sensibly  exceeds  in  weight  the  starch  em- 
ployed. Dextrin  itself  has  exactly  the  same  composition  as  the  original 
starch. 

Dextrin  is  used  in  the  arts  as  a  substitute  for  gum ;  it  is  sometimes  made 
in  the  manner  above  described,  but  more  frequently  by  heating  dry  potato- 
starch  to  400°  (204° -oC),  by  which  it  acquires  a  yellowish  tint  and  becomes 
soluble  in  cold  water.  It  is  sold  in  this  state  under  the  appellation  of  British 
Gum. 

Starch  is  an  important  article  of  food,  especially  when  associated,  as  in 
ordinary  meal,  with  albuminous  substances.  Arrow-root,  and  the  fecula  of 
the  Canna  coccinea,  are  very  pure  varieties,  employed  as  articles  of  diet ; 
arrow-root  is  obtained  from  the  Maranta  arundinacea,  cultivated  in  the  West 
Indies  ;  it  is  with  difficulty  distinguished  from  potato-starch.  Tapioca  is 
prepared  from  the  root  of  the  latropha  manihot,  being  thoroughly  purified 
from  its  poisonous  juice.  Cassava  is  the  same  substance  modified  while 
moist  by  heat.  Sago  is  made  from  the  soft  central  portion  of  the  stem  of  a 
palm-tree. 

Starch  from  Iceland  Moss.  —  The  lichen  called  Cetraria  Mandica,  puri- 
fied by  a  little  cold  solution  of  potassa  from  a  bitter  principle,  yields  when 
boiled  in  water  a  slimy  and  nearly  colourless  liquid,  which  gelatinizes  on 
cooling,  and  dries  up  to  a  yellowish  amorphous  mass,  which  does  not  dissolve 
in  cold  water,  but  merely  softens  and  swells.  A  solution  of  this  substance 
in  warm  water  is  not  affected  by  iodine,  although  the  jelly,  on  the  contrary, 
is  rendered  blue.  It  is  precipitated  by  alcohol,  acetate  of  lead,  and  infusion 
of  galls,  and  is  converted  by  boiling  with  dilute  sulphuric  acid  into  grape- 
sugar.  According  to  Mulder,  linen-starch  likewise  contains  Q24^2QOiQ.  The 
jelly  from  certain  algoi,  as  that  of  Ceylon,  and  the  so-called  Carragheen  moss^ 
closely  resembles  the  above. 

Inultn.  —  This  substance,  which  differs  from  common  starch  in  some  im 
portant  particulars,  is  found  in  the  root  of  the  Tnula  helenium.  the  Helianthut 


840  auM. 

iuberosus,  the  dahlia,  and  several  other  plants ;  it  may  be  easily  obtained  by 
washing  the  rasped  root  on  a  sieve,  and  allowing  the  inulin  to  settle  down 
from  the  liquid ;  or  by  cutting  the  root  into  thin  slices,  boiling  these  in 
water,  and  filtering  while  hot ;  the  inulin  separates  as  the  solution  cools.  It 
is  a  white,  amorphous,  tasteless  substance,  nearly  insoluble  in  cold  water, 
but  freely  dissolved  by  the  aid  of  heat ;  the  solution  is  precipitated  by  alco- 
hol, but  not  by  acetate  of  lead  or  infusion  of  galls.  Iodine  communicates  a 
brown  colour.  Inulin  has  been  analyzed  by  Mr.  Parnell,  who  finds  it  to 
contain,  when  dried  at  212°  (100°G),  C24H2,02,. 

Gum.  —  Gum-Arabic,  which  is  the  produce  of  an  acacia,  may  be  taken  as 
the  most  perfect  type  of  this  class  of  bodies.  In  its  purest  and  finest  con- 
dition, it  forms  white  or  slightly  yellowish  irregular  masses,  which  are  des- 
titute of  crystalline  structure,  and  break  with  a  smooth  conchoidal  fracture. 
It  is  soluble  in  cold  water,  forming  a  viscid,  adhesive,  tasteless  solution, 
from  which  the  pure  soluble  gummy  principle,  or  arabin,  is  precipitated  by 
alcohol  and  by  basic  acetate  of  lead,  but  not  by  the  neutral  acetate.'  Ara- 
bin is  composed  of  C24H22O22,  and  is  consequently  isomeric  with  crystallized 
cane-sugar. 

Mucilage,  so  abundant  in  linseed,  in  the  roots  of  the  mallow,  in  salep,  the 
fleshy  root  of  Oi'chis  mascula,  and  in  other  plants,  differs  in  some  respects 
from  the  foregoing,  although  it  agrees  in  the  property  of  dissolving  in  cold 
water.  The  solution  is  less  transparent  than  that  of  gum,  and  is  precipi- 
tated by  neutral  acetate  of  lead.  Gum  iragacanth  is  chiefly  composed  of  a 
kind  of  mucilage  to  which  the  name  bassorin  has  been  given,  and  which 
refuses  to  dissolve  in  water,  merely  softening  and  assuming  a  gelatinous 
aspect.  It  is  dissolved  by  caustic  alkali.  Cerasin  is  the  term  given  to  the 
insoluble  portion  of  the  gum  of  the  cherry-tree ;  it  resembles  bassorin.  The 
composition  of  these  various  substances  has  been  carefully  examined  by  M. 
Schmidt,  who  finds  that  it  closely  agrees  with  that  of  starch.  Mucilage  in- 
variably contains  hydrogen  and  oxygen  in  the  proportion  in  which  they  form 
water,  and  when  treated  with  acid,  yeild  grape-sugar. 

Pectin,  or  the  jelly  of  fruits,  is,  in  its  physical  properties,  closely  allied  to 
the  foregoing  bodies.  It  may  be  extracted  from  various  vegetable  juices  by 
precipitation  by  alcohol.  It  forms,  when  moist,  a  transparent  jelly,  soluble 
in  water,  and  tasteless,  which  dries  up  to  a  translucent  mass.  It  is  to  this 
substance  that  the  firm  ^consistence  of  currant  and  other  fruit  jellies  is 
to  be  ascribed.  According  to  M.  Fremy,  the  composition  of  pectin  is 
C'64^48^64-  -^y  ebullition  with  water  and  with  dilute  acids  it  is  changed  into 
two  isomeric  modifications,  to  which  the  names  parapectin  and  metapectin 
have  been  given.  In  contact  with  bases,  these  three  substances  become 
converted  into  pectic  acid,  which,  except  that  it  possesses  feeble  acid  proper- 
ties, and  is  insoluble  in  water,  resembles  in  the  closest  manner  pectin  itself. 
By  long  boiling  with  solution  of  caustic  alkali,  a  farther  change  is  produced, 
and  a  new  acid,  the  metapectic,  developed,  which  does  not  gelatinize.  The 
salts  of  these  two  acids  are  incapable  of  crystallizing.  Their  composition 
is  represented  by  the  following  formulee  : — 

Pectic  acid 2HO,C32H2o02g 

Metapectic  acid 2HO,C24Hi502 

Much  doubt  still  exists  respecting  the  composition  of  the  various  bodies  of 
the  pectin-series ;  they  do  not  appear,  from  the  analyses  yet  made,  to  con 

*  The  precipitate  produced  by  sub-salts  of  lead  is  a  compound  of  arabine  and  oxide  of  lead, 
CVHmOM-f  2PbO.  By  the  action  of  very  dilute  sulphuric  acid  arabine  is  slowly  changed  into 
dextrine,  and  by  proloneed  contact  into  glucose.  Nitric  acid  decomposes  gum  and  produceB 
first  mucic  and  ultimately  oxalic  acid. — JK.  B. 


OXALIC   ACID.  341 

tain  oxygen  and  hydrogen  in  equal  equivalents,  and  consequently  scarcely 
belong  to  the  starch-group. 

Lignin;  ceclulose. — This  substance  constitutes  the  fundamental  mate- 
rial of  the  structure  of  plants ;  it  is  employed  in  the  organization  of  cells, 
and  vessels  of  all  kinds,  and  forms  a  large  proportion  of  the  solid  parts  of 
every  vegetable.  It  must  not  be  confounded  with  ligneous  or  woody  tissue, 
which  is  in  reality  cellulose,  with  other  substances  superadded,  which  encrust 
the  walls  of  the  original  membraneous  cells,  and  confer  stiffness  and  inflex- 
ibility. Thus  woody  tissue,  even  when  freed  as  much  as  possible  from 
colouring  matter  and  resin  by  repeated  boiling  with  water  and  alcohol, 
yields  on  analysis  a  result  indicating  an  excess  of  hydrogen  above  that 
required  to  form  water  with  the  oxygen,  besides  traces  of  nitrogen.  Pure 
cellulose,  on  the  other  hand,  is  a  terniary  compound  of  carbon  and  the  ele- 
ments of  water,  closely  allied  in  composition  to  starch,  if  not  actually 
isomeric  with  that  substance.* 

The  properties  of  lignin  may  be  conveniently  studied  in  fine  linen  or 
cotton,  which  are  almost  entirely  composed  of  the  body  in  question,  the 
associated  vegetable  principles  having  been  removed  or  destroyed  by  the 
variety  of  treatment  to  which  the  fibre  has  been  subjected.  Pure  lignin  is 
tasteless,  insoluble  in  water  and  alcohol,  and  absolutely  innutritions  ;  it  is 
not  sensibly  affected  by  boiling  water,  unless  it  happen  to  have  been  derived 
from  a  soft  or  imperfectly  developed  portion  of  the  plant,  in  which  case  it  is 
disintegrated  and  rendered  pulpy.  Dilute  acids  and  alkalis  exert  but  little 
action  on  lignin,  even  at  a  boiling  temperature ;  strong  oil  of  vitriol  converts 
it,  in  the  cold,  into  a  nearly  colourless,  adhesive  substance,  which  dissolves 
in  water,  and  presents  the  character  of  dextrin.  This  curious  and  interest- 
ing experiment  may  be  conveniently  made  by  very  slowly  adding  concen- 
trated sulphuric  acid  to  half  its  weight  of  lint,  or  linen  cut  into  small  shreds, 
taking  care  to  avoid  any  rise  of  temperature,  which  would  be  attended  with 
charring  or  blackening.  The  mixing  is  completed  by  trituration  in  a  mor- 
tar, and  the  whole  left  to  stand  a  few  hours ;  after  which  it  is  rubbed  up 
with  water,  and  warmed,  and  filtered  from  a  little  insoluble  matter.  The 
solution  may  then  be  neutralized  with  chalk,  and  again  filtered.  The  gummy 
liquid  retains  lime,  partly  in  the  state  of  sulphate,  and  partly  in  combina- 
tion with  a  peculiar  acid,  composed  of  the  elements  of  sulphuric  or  hypo- 
sulphuric  acid,  in  union  with  those  of  the  lignin,  to  which  the  name  sulpho- 
lignic  acid  is  given.  If  the  liquid,  previous  to  neutralization,  be  boiled 
during  three  or  four  hours,  and  the  water  replaced  as  it  evaporates,  the 
dextrin  becomes  entirely  changed  to  grape-sugar.  Linen  rags  may,  by 
these  means,  be  made  to  furnish  more  than  their  own  weight  of  that  sub- 
stance. 

Lignin  is  not  coloured  by  iodine. 


PKODUCTS    ARISING    FROM    THE    ALTERATION    OP   THE    PRECEDING     SUBSTANCES 
BY    CHEMICAL    AGENTS. 

ACTION  OF  NITRIC  ACID. 

Oxalic  Acid,  Q^O^MO-^-^TiO. — This  important  compound  occurs  ready 
formed  in  several  plants,  in  combination  with  potassa  as  an  acid  salt,  or 
with  lime.     It  is  now  manufactured  in  large  quantities  as  an   article  of 

>  Dumas,  Chimie  appliquee  aux  Arts,  vi.  6. 

29* 


M2  OXALICACID. 

commerce,  by  the  action  of  nitric  acid  on  sugar,  starch,  and  dextrin.  With 
the  exception  of  gum  and  sugar  of  milk,  which  yield  another  product,  all 
the  substances  comprehended  in  the  saccharine  and  starch  group  furnish 
oxalic  acid,  as  the  chief  and  characteristic  result  of  the  long-continued 
action  of  moderately  strong  nitric  acid  at  an  elevated  temperature. 

One  part  of  sugar  is  gently  heated  in  a  retort  with  5  parts  of  nitric  acid 
of  sp.  gr.  1-42,  diluted  with  twice  its  weight  of  water;  copious  red  fumes 
are  disengaged,  and  the  oxidation  of  the  sugar  proceeds  with  violence  and 
rapidity.  When  the  action  slackens,  heat  may  be  again  applied  to  the 
vessel,  and  the  liquid  concentrated,  by  distilling  off"  the  superfluous  nitric 
acid,  until  it  deposits  crystals  on  cooling.  These  are  drained,  re-dissolved 
in  a  small  quantity  of  hot  water,  and  the  solution  set  aside  to  cool.  The 
acid  separates  from  a  hot  solution  in  colourless,  transparent  crystals  derived 
from  an  oblique  rhombic  prism,  which  contain  three  equivalents  of  water, 
one  of  these  being  basic  and  inseparable,  except  by  substitution ;  the  other 
two  may  be  expelled  by  a  very  gentle  heat,  the  crystals  crumbling  down  to 
a  soft  white  powder,  which  may  be  sublimed  in  great  measure  without 
decomposition.  The  crystallized  acid,  on  the  contrary,  is  decomposed  by  a 
high  temperature  into  carbonic  and  formic  acids  and  carbonic  oxide,  without 
Bolid  residue. 

The  crystals  of  oxalic  acid  dissolve  in  8  parts  of  water  at  60°  (15°-5C),  and 
in  their  own  weight,  or  less,  of  hot  water ;  they  are  also  soluble  in  spirit. 
The  aqueous  solution  has  an  intensely  sour  taste  and  most  powerful  acid  re- 
action, and  is  highly  poisonous.  The  proper  antidote  is  chalk  or  magnesia. 
Oxalic  acid  is  decomposed  by  hot  oil  of  vitriol  into  a  mixture  of  carbonic 
oxide  and  carbonic  acid ;  it  is  slowly  converted  into  carbonic  acid  by  nitric 
acid,  whence  arises  a  considerable  loss  in  the  process  of  manufacture.  The 
binoxides  of  lead  and  manganese  effect  the  same  change,  becoming  reduced 
to  protoxides,  which  combine  with  the  unaltered  acid. 

Oxalic  acid  is  formed  from  sugar  by  the  replacement  of  the  whole  of  its 
hydrogen  by  an  equivalent  quantity  of  oxygen. 

1    eq.  sugar   =C24HjgOig) /  12  eq.  oxalic  acid= €554      0^ 

36  eq.  oxygen=  Ogg  j  "~  1 18  eq.  water         =      HjgOjg 


C24H18O54  ^24^18^54 

The  most  important  salts  of  oxalic  acid  are  the  following : — 

Neutral  oxalate  of  potassa,  KO,C203-j-HO. — This  is  prepared  by 
neutralizing  oxalic  acid  by  carbonate  of  potassa.  It  crystallizes  in  transpa- 
rent rhombic  prisms,  which  become  opaque  and  anhydrous  by  heat,  and  dis- 
solve in  3  parts  of  water.  Oxalate  of  potassa  is  often  produced  when  a 
variety  of  organic  substances  are  cautiously  heated  with  excess  of  caustic 
alkali. 

BiNoxALATE  OP  POTASSA,  KO,2C20g-(-3HO. — Sometimes  called  salt  of 
sorrel,  from  its  occurrence  in  that  plant.  This,  or  the  substance  next  to  be 
mentioned,  is  found  also  in  the  rumez  and  oxalis  acetosella,  and  in  the  garden 
rhubarb,  associated  with  malic  acid.  It  is  easily  prepared  by  dividing  a  so- 
lution of  oxalic  acid,  in  hot  water,  into  two  equal  portions,  neutralizing  one 
with  carbonate  of  potassa,  and  adding  the  other;  the  salt  crystallizes  on 
cooling,  in  colourless  rhombic  prisms.  The  crystals  have  a  sour  taste,  and 
require  40  parts  of  cold,  and  6  of  boiling  water  for  solution. 

QuADKOXALATE  OF  POTASSA,  KO,4C203-}- 7H0. — Prepared  by  a  process 
similar  in  principle  to  that  last  described.  The  crystals  are  modified  octahe- 
drons, and  are  less  soluble  than  those  of  the  binoxalate,  which  the  salt  in 
other  respects  resembles. 

Oxalate  of  soda,  NaOjCjOj,  has  but  little  solubility;  a  binoxalate  exists. 


OXALIC    ACID.  343 

Oxalate  op  ammonia,  NH40,C203-f  HO.  —  This  beautiful  salt  is  prepared 
by  neutralizing  by  carbonate  of  ammonia  a  hot  solution  of  oxalic  acid.  It 
crystallizes  in  long,  colourless,  rhombic  prisms,  which  effloresce  in  dry  air 
from  loss  of  water  of  crystallization.  They  are  not  very  soluble  in  cold 
water,  but  freely  dissolve  by  the  aid  of  heat.  Oxalate  of  ammonia  is  of  great 
value  in  analytical  chemistry,  being  employed  to  precipitate  lime  from  its 
solutions.  When  oxalate  of  ammonia  is  heated  in  a  retort,  it  is  completely 
decomposed,  yielding  water,  ammonia  and  carbonate  of  ammonia,  cyanogen 
and  carbonic  acid  gases,  and  a  small  quantity  of  a  peculiar  greyish  white 
sublimate.  The  latter  bears  the  name  of  oxamide ;  it  is  a  very  remarkable 
body,  and  forms  the  type  of  a  large  class  of  substances  containing  the  ele- 
ments of  an  ammoniacal  salt,  minus  those  of  water.  Oxamide  is  composed 
of  CgHgNOg,  i.e.,  NH40,C203 — 2H0,  or  the  elements  of  1  eq.  amidogen,  and 
2  eq.  carbonic  oxide.  It  is  insoluble  in  water  and  alcohol :  when  boiled  with 
an  alkali  it  furnishes  an  oxalate  of  the  base,  and  ammonia,  which  is  expelled; 
and  when  heated  with  an  acid,  it  produces  an  ammoniacal  salt.  When  treated 
with  nitrous  acid  it  likewise  reproduces  oxalic  acid,  pure  nitrogen  being 
evolved  C2H2N02+N03=C203,H0-f.H04.2N.  Oxamide  is  the  representa- 
tive of  a  tolerably  large  class  of  bodies  having  very  analogous  chemical  rela- 
tions, and  apparently  a  common  constitution.  Oxamide  is  obtained  purer 
and  more  abundantly  from  oxalic  ether ;  its  preparation  will  be  found  des- 
cribed under  the  head  of  that  substance.  Oxalate  of  ammonia,  when  dis- 
tilled with  anhydrous  phosphoric  acid,  loses  four  equivalents  of  water  and 
yields  a  considerable  quantity  of  cyanogen,  NH40,C203  —  4H0  =  C^N.  There 
are,  however,  other  compounds  simultaneously  produced. 

The  hinoxalate  of  ammonia  is  still  less  soluble  than  the  oxalate.  When 
this  salt  is  heated  in  an  oil-bath  to  450°  (232° -20),  among  other  products  an 
acid  called  the  ozamic  is  generated,  containing  C4HjN05,HO,  i.e.,  NH4O, 
CjOg.HOjCaOj  —  2H0,  and  may  be  viewed  as  a  compound  of  oxalic  acid  with 
oxamide.  It  forms  soluble  compounds  with  lime  and  baryta.  When  heated 
with  alkalis  it  yields  ammonia  and  oxalate ;  hot  oil  of  vitriol  resolves  it  into 
carbonic  oxide  and  carbonic  acid ;  and  water  converts  it,  at  a  boiling  tem- 
perature, into  binoxalate  of  ammouia.  Oxamic  acid  too,  is  interesting  as  the 
type  of  a  very  large  class  of  similarly  constructed  compounds. 

Oxalate  op  lime,  CaO,C203-|-2HO. — This  compound  is  formed  whenever 
oxalic  acid  or  an  oxalate  is  added  to  a  soluble  salt  of  lime ;  it  falls  as  a  white 
powder,  which  acquires  density  by  boiling,  and  is  but  little  soluble  in  hydro- 
chloric, and  entirely  insoluble  in  acetic  acid.  Nitric  acid  dissolves  it  easily. 
When  dried  at  212°  (100°C)  it  retains  an  equivalent  of  water,  which  may  be 
driven  oiF  by  a  rather  higher  temperature.  Exposed  to  a  red-heat  in  a  close 
vessel,  it  is  converted  into  carbonate  of  lime,  with  escape  of  carbonic  oxide. 

The  oxalates  of  baryta,  zinc,  manganese,  protoxide  of  iron,  copper,  nickel,  and 
cobalt,  are  nearly  insoluble  in  water;  that  of  magnesia  is  sparingly  soluble, 
and  that  of  the  sesquioxide  of  iron  freely  soluble.  The  double  oxalate  of  chro- 
mium and  potassa,  made  by  dissolving  in  hot  water  1  part  bichromate  of  po- 
tassa,  2  parts  binoxalate  of  potassa,  and  2  parts  crystallized  oxalic  acid,  is 
one  of  the  most  beautiful  salts  known.  The  crystals  appear  black  by  re- 
tiected  light  from  the  intensity  of  their  colour,  which  is  pure  deep  blue  ; 
they  are  very  soluble.  The  salt  contains  3(KO,C203)  -f  Cr203,3C203-f  HO.  A 
corresponding  compound  containing  sesquioxide  of  iron  has  been  formed ;  it 
crystallizes  freely,  and  has  a  beautiful  green  colour. 

Saccharic  acid,  CgH407,HO.  —  This  substance  was  once  thought  to  be 
identical  with  malic  acid,  which  is  not  the  case ;  it  is  formed  by  the  action 
of  dilute  nitric  acid  on  sugar,  and  is  often  produced  in  the  preparation  of 
oxalic  acid,  being,  from  its  superior  solubility,  found  in  the  mother-liquor 
from  which  the  oxalic  acid  has  crystallized.     It  may  be  made  by  heating  to- 


344  SACCHARIC    ACID. 

gether  1  part  sugar,  2  parts  nitric  acid,  and  10  parts  water.  When  the  re- 
action seems  terminated,  the  acid  liquid  is  diluted,  neutralized  with  chalk, 
and  the  filtered  liquid  mixed  with  acetate  of  lead.  The  insoluble  saccharate 
of  lead  is  washed,  and  decomposed  by  sulphuretted  hydrogen  The  acid 
slowly  crystallizes  from  a  solution  of  syrupy  consistence  in  long  colourless 
needles ;  it  has  a  sour  taste,  and  forms  soluble  salts  with  lime  and  baryta. 
When  mixed  with  nitrate  of  silver,  it  gives  no  precipitate,  but,  on  the  addi- 
tion of  ammonia,  a  while  insoluble  substance  separates,  which  is  reduced, 
by  gently  warming  the  whole,  to  metallic  silver,  the  vessel  being  lined  with 
a  smooth  and  brilliant  coating  of  the  metal.  Nitric  acid  converts  the  sac- 
charic into  oxalic  acid. 

Xyloidin  and  pyroxylin. — When  starch  is  mixed  with  nitric  acid  of  spe- 
cific gravity  1-5,  it  is  converted  without  disengagement  of  gas  into  a  trans- 
parent, colourless  jelly,  which,  when  put  into  water,  yields  a  white,  curdy, 
insoluble  substance :  this  is  the  new  body  xyloidin.  When  dry,  it  is  white 
and  tasteless,  insoluble  even  in  boiling  water,  but  freely  dissolved  by  dilute 
nitric  acid,  and  the  solution  yields  oxalic  acid  when  boiled.  Other  sub- 
stances belonging  to  the  same  class  also  yield  xyloidin ;  paper  dipped  into 
the  strongest  nitric  acid,  quickly  plunged  into  water,  and  afterwards  dried, 
becomes  in  great  part  so  changed;  it  assumes  the  appearance  of  parchment, 
and  acquires  an  extraordinary  degree  of  combustibility. 

If  pure  finely  divided  ligneous  matter,  as  cotton-wool,  be  steeped  for  a 
few  minutes  in  a  mixture  of  nitric  acid  of  sp.  gr.  1  -5  and  concentrated  sul- 
phuric acid,  squeezed,  thoroughly  washed  and  dried  by  very  gentle  heat,  it 
will  be  found  to  have  increased  in  weight  about  70  per  cent.,  and  to  have  be- 
come in  the  highest  degree  explosive,  taking  fire  at  a  temperature  not  much 
above  300°  (148° -80),  and  burning  without  smoke  or  residue.  This  is 
pyroxylin,  the  gun-cotton  of  Professor  Schoenbein.  It  difi^ers  from  xyloidin 
in  composition,  in  its  mode  of  combustion,  and  in  resisting  the  action  of  cer- 
tain liquids,  as  ether  containing  a  little  alcohol,  which  dissolve  xyloidin  with 
facility.  To  a  solution  of  this  description  the  name  collodion  has  been  given  ; 
it  is  used  in  surgery. 

Both  xyloidin  and  pyroxylin  appear  to  the  substitution-compounds,  in 
which  the  elements  of  hyponitric  acid  replace  Tespectively  3  and  5  equiva- 
lents of  hydrogen  in  those  of  water  in  starch  and  lignin.  The  analytical 
results  are  not  very  uniform,  but  the  formulae  which  best  agree  with  them 
are,  xyloidin  C24H,7N3032,  and  pyroxylin  C24H,5N504o.' 

An  analogous  compound  is  produced  by  the  action  of  nitric  acid  upon 
mannite  (vide  p.  337).  This  substance  may  be  crystallized  from  spirit,  and 
contains  CgH^NgOig ;  it  may  be  viewed  as  mannite,  in  which  three  equiva- 
lents of  hydrogen  are  replaced  by  hyponitric  acid. 

Mucic  ACID  C,2HgO,4,2HO.  — Sugar  of  milk  and  gum,  heated  with  nitric 
acid  somewhat  diluted,  furnish,  in  addition  to  a  small  quantity  of  oxalic  acid, 

'  Pyroxylin  obtained  by  the  mixture  of  nitric  and  sulphuric  acids,  or  by  the  action  of  a 
well  cooled  mixture  of  two  parts  of  nitrate  of  potassa  and  three  parts  of  concentrated  sul- 
phuric acid,  has  the  composition  as  given  in  the  text,  but  is  wholly  insoluble  in  ether,  or  a 
mixture  of  ether  and  alcohol.  When,  however,  the  cotton-wool  is  steeped  in  the  mixture  of 
nitre  and  sulphuric  acid  at  the  temperature  produced  by  their  mixture,  the  resulting  com- 
pound is  readily  soluble  in  ether  and  a  mixture  of  ether  and  alcohol  forming  a  transparent, 
viscid  solution.  Ammonia  passed  through  this  solution  renders  it  quite  fluid.  The  ammo- 
uiacal  solution  acted  on  by  a  large  quantity  of  water  yields  a  light  white  precipitate,  inso- 
luble in  water,  while  nitrate  of  ammonia  remains  in  solution.  The  composition  of  the  pre- 
cipitate is  intermediate  between  xyloidin  and  pyroxylin,  CQ4H16N4O36  four  equivalents  ot 
hydrogen  being  replaced  by  four  of  hyponitric  acid  or  four  equivalents  of  the  elements  of 
V  ater  by  four  of  nitric  acid.  It  may  be  dried  without  alteration  at  the  boiling  temperature ; 
by  heat  it  explodes  with  a  slight  residue  of  carbon. 

The  mixture  of  sulphuric  and  nitric  acid  forms  from  gum,  glucose,  and  dextrine,  explosive 
products  wh''h  have  not  yet  been  fully  examined.  (Bechamp.  Ann.  Ch.  et  Phys.  FeU 
185?^  — E.B 


FERMENTATION     OF    &UGAR  845 

a  wliito  nearly  insoluble  substance  called  mucic  acid.  It  may  be  easily  pre- 
pared by  heating  togethe*Hn  a  flask  or  retort  1  part  of  milk-sugar,  or  gum, 
4  parts  of  nitric  acid,  and  1  of  water ;  the  mucic  acid  is  afterwards  collected 
upon  a  filter,  washed  and  dried.  It  has  a  slightly  sour  taste,  reddens  vege- 
table colours,  and  forms  salts  with  bases.  It  requires  for  solution  66  parts 
of  boiling  water.  Oil  of  vitriol  dissolves  it  with  red  colour.  Mucic  acid  is 
decomposed  by  heat,  yielding,  among  other  products,  a  volatile  acid,  the 
pyromucic,  which  is  soluble  in  water,  and  crystallizes  in  a  form  resembling 
that  of  benzoic  acid.    Pyromucic  acid  is  monobasic ;  it  contains  CjoHjOg.HO. 

Suberic  acid,  Ci5H,20g,2HO,  is  formed  by  the  action  of  nitric  acid  on  the 
peculiar  ligneous  matter  of  cork,  and  also  on  certain  fatty  bodies ;  it  much 
resembles  mucic  acid,  but  is  more  soluble  in  water.  It  is  a  bibasic  acid. 
See  farther  on,  Section  VII.,  Oils  and  Fats. 

The  following  bodies  are  closely  allied  in  composition  to  oxalic  acid : — 

Mellitic  acid,  0403,110. — This  substance  occurs,  in  combination  with 
alumina,  in  a  very  rare  mineral  called  mellite  or  honey-stone,  found  in  deposits 
of  imperfect  coal,  or  lignite.  It  is  soluble  in  water  and  alcohol,  and  is  crys- 
tallizable,  forming  colourless  needles.  It  combines  with  bases :  the  melli- 
tates  of  the  alkalis  are  soluble  and  crystallizable ;  those  of  the  earths  and 
metals  proper  are  mostly  insoluble. 

Mellitate  of  ammonia  yields  by  distillation  two  curious  compounds,  para- 
niide  and  euchronic  acid.  The  former  is  a  white,  amorphous,  insoluble  sub- 
stance, containing  CgHN04,  (i.e.,  bimellitate  of  ammonia — 4  eq.  of  water), 
and  convertible  by  boiling  with  water  into  bimellitate  of  ammonia.  The 
latter  forms  colourless,  sparingly  soluble  crystals  containing  in  the  anhy- 
drous state  C,jN0g,2H0.  In  contact  with  metallic  zinc  and  deoxidizing 
agents  in  general,  euchronic  acid  yields  a  deep  blue  insoluble  substance  called 
euchrone. 

Rhodizonic  and  croconic  acids. — When  potassium  is  heated  in  a  stream 
of  dry  carbonic  oxide  gas,  the  latter  is  absorbed  in  large  quantity,  and  a 
black  porous  substance  generated,  which,  when  put  into  water,  evolves  in- 
flammable gas,  and  produces  a  deep  red  solution  containing  the  potassa-salt 
of  a  peculiar  acid;  the  rhodizonic;  by  adding  alcohol  to  the  liquid,  th^j  rho- 
dizonate  of  potassa  is  precipitated.  This  and  the  lead-salt  are  the  only  two 
compounds  which  have  been  fully  examined ;  the  acid  itself  cannot  be  iso- 
lated. Rhodizonate  of  potassa  is  composed  of  C^O^SKO ;  hence  the  acid 
would  appear  to  be  tribasic. 

When  solution  of  rhodizonate  of  potassa  is  boiled,  it  becomes  orange-yel- 
low from  decomposition  of  the  acid,  and  is  then  found  to  contain  oxalate  of 
potassa,  free  potassa,  and  a  salt  of  an  acid  to  which  the  term  croconic  is 
applied.  This  acid  can  be  isolated ;  it  is  yellow,  easily  crystallizable,  and 
soluble  both  in  water  and  alcohol.  Crystallized  croconic  acid  contains 
CA^HO. 

THE    FERMENTATION    OF    SUGAR,    AND    ITS    PRODUCTS. 

The  term  fermentation  is  applied  in  chemistry  to  a  peculiar  metamorpho- 
sis of  a  complex  organic  substance,  by  a  transportation  of  its  elements  under 
the  agency  of  an  external  disturbing  force,  different  from  ordinary  chemical 
attraction,  and  more  resembling  those  obscure  phenomena  of  contact  already 
noticed,  to  which  the  expression  katalysis  is  sometimes  applied.  The  expla 
nation  which  Liebig  has  suggested  of  the  cause  and  nature  of  the  fermen- 
tative change  is  a  very  happy  one,  although  of  necessity  only  hypothetical 
It  has  long  been  known  that  one  of  the  most  indispensable  conditions  of  tkal 
process  is  the  presence  in  the  fermenting  liquid  of  certain  azotized  substan- 
ces, called  ferments,  whose  decomposition  proceeds  simultaneously  with  that 
of  the  body  undergoing  metamorphosis.     They  all  belong  to  the  class  of  al  • 


346  FERMENTATION     OF     SUGAR. 

buminous  principles,  bodies  which  in  a  moist  condition  putrefy  and  decom- 
pose spontaneously.  It  is  imagined  that  when  thUse  substances,  in  the  act 
of  undergoing  change,  are  brought  into  contact  with  neutral  ternary  com- 
pounds of  small  stability,  as  sugar,  the  molecular  disturbance  of  the  body, 
already  in  a  state  of  decomposition,  may  be,  as  it  were,  propagated  to  the 
other,  and  bring  about  destruction  of  the  equilibrium  of  forces  to  which  it 
owes  its  being.  The  complex  body  under  these  circumstances,  breaks  up 
into  simpler  products,  which  possess  greater  permanence.  Whatever  may 
be  the  ultimate  fate  of  this  ingenious  hypothesis,  it  is  certain  that  decom- 
posing azotized  bodies  not  only  do  possess  very  energetic  and  extraordinary 
powers  of  exciting  fermentation,  but  that  the  kind  of  fermentation  set  up  is, 
in  a  great  degree,  dependent  on  the  phase  or  stage  of  decomposition  of  the 
ferment. 

Alcohol  ;  vinous  fermentation.  —  A  solution  of  pure  sugar,  in  an  open 
or  close  vessel,  may  be  preserved  unaltered  for  any  length  of  time ;  but,  if 
putrescible  azotized  matters  be  present,  in  the  proper  state  of  decay,  the 
sugar  is  converted  into  alcohol,  with  escape  of  carbonic  acid.  Putrid  blood, 
white  of  egg,  or  flour-paste,  will  efl'ect  this;  by  far  the  most  potent  alcoholic 
ferment  is,  however,  to  be  found  in  the  insoluble,  yellowish,  viscid  matter 
deposited  from  beer  in  the  act  of  fermentation,  called  yeast.  If  the  sugar 
be  dissolved  in  a  large  quantity  of  water,  a  due  proportion  of  active  yeast 
added,  and  the  whole  maintained  at  a  temperature  of  70°  (21 -IC)  or  80° 
(26° -60),  the  change  will  go  on  with  great  rapidity.  The  gas  disengaged 
will  be  found  to  be  nearly  pure  carbonic  acid ;  it  is  easily  collected  and  ex- 
amined, as  the  fermentation,  once  commenced,  proceeds  perfectly  well  in  a 
close  vessel,  as  a  large  bottle  or  flask,  fitted  with  a  cork  and  conducting- 
tube.  When  the  efi'ervescence  is  at  an  end,  and  the  liquid  has  become  clear, 
it  will  yield  alcohol  by  distillation.  Such  is  the  origin  of  this  important  com- 
pound ;  it  is  a  product  of  the  metamorphosis  of  sugar,  under  the  influence 
of  a  ferment. 

The  composition  of  alcohol  is  expressed  by  the  formula  C4Hg02 :  it  is  pro- 
duced by  the  breaking  up  of  an  equivalent  of  grape-sugar,  C24H2g02g,  into 
4  eq.  of  alcohol,  8  of  carbonic  acid,  and  4  of  water.  It  is  grape-sugar  alone 
which  yields  alcohol,  the  ferment  in  the  experiment  above  related  first  con- 
verting the  cane-sugar  into  that  substance.  Milk-sugar  may  sometimes  appa- 
rently be  made  to  ferment,  but  a  change  into  grape-sugar  always  really  pre- 
cedes the  production  of  alcohol. 

The  spirit  first  obtained  by  distilling  a  fermented  saccharine  liquid  is  very 
weak,  being  diluted  with  a  large  quantity  of  water.  By  a  second  distilla- 
tion, in  which  the  first  portions  of  the  distilled  liquid  are  collected  apart,  it 
may  be  greatly  strengthened ;  the  whole  of  the  water  cannot,  however,  be 
thus  removed.  The  strongest  rectified  spirit  of  wine  of  commerce  has  a 
density  of  about  0-8.35,  and  yet  contains  13  or  14  per  cent,  of  water.  Pure 
or  absolute  alcohol  may  be  obtained  from  this  by  re-distilling  it  with  half  its 
weight  of  fresh  quick-lime.  The  lime  is  reduced  to  coarse  powder,  and  put 
into  a  retort;  the  alcohol  is  added,  and  the  whole  mixed  by  agitation.  The 
neck  of  the  retort  is  securely  stopped  with  a  cork,  and  the  mixture  left  for 
aeveral  days.     The  alcohol  is  distilled  off  by  the  heat  of  a  watei'-bath. 

Pure  alcohol  is  a  colourless,  limpid  liquid,  of  pungent  and  agreeiible  taste 
and  odour;  its  specific  gravity  at  60°  (15°-5C)  is  0-7938,  and  that  of  its 
vapour  l-Olo,  It  is  very  inflammable,  burning  with  a  pale  bluish  flame,  free 
trom  smoke,  and  has  never  been  fi-ozen.  Alcohol  boils  at  173°  (78°-lC)  when 
hi  the  anhydrous  condition  ;  in  a  diluted  state  the  boiling-point  is  higher, 
being  progressively  raised  by  each  addition  of  water.  In  the  act  of  dilution 
a  contraction  of  volume  occurs,  and  the  temperature  of  the  mixture  rises 
many  degrees,  tlr^s  takes  place  not  only  with  pure  alcohol,  but  with  rectified 


ALCOHOL.  S4T 

spirK.  It  is  miscihlc  with  water  in  all  proportions,  and,  indeed,  has  a  great 
attraction  for  the  latter,  absorbing  its  vapour  from  the  air,  and  abstracting 
the  moisture  from  membranes  and  other  similar  substances  immersed  in  it. 
The  solvent  powers  of  alcohol  are  very  extensive ;  it  dissolves  a  great  num- 
ber of  saline  compounds,  and  likewise  a  considerable  proportion  of  potassa. 
With  many  of  these  substances  it  forms  definite  compounds.  The  substance 
which  is  produced  by  potassa,  contains  C4H50,KO ;  it  may  be  likewise  formed 
by  acting  with  potassium  upon  anhydrous  alcohol,  when  hydrogen  is  evolved. 
Alcohol  dissolves,  moreover,  many  organic  substances,  as  the  vegeto-alkalis, 
resins,  essential  oils,  and  various  other  bodies;  hence  its  great  use  in  chemi- 
cal investigations  and  in  several  of  the  arts. 

The  strength  of  commercial  spirit  is  inferred  from  its  density,  when  free 
from  sugar  and  other  substances  added  subsequent  to  distillation ;  a  table 
exhibiting  the  proportions  of  real  alcohol  and  water  in  spirits  of  different 
densities  will  be  found  at  the  end  of  the  volume.  The  excise  proof  spirit  has 
a  sp.  gr,  of  0-91Q8  at  60°  (15° -SC),  and  contains  49J  per  cent,  by  weight  of 
real  alcohol. 

Wine,  beer,  &c.,  owe  their  intoxicating  properties  to  the  alcohol  they  con- 
tain, the  quantity  of  which  varies  very  much.  Port  and  sherry,  and  some 
other  strong  wines,  contain,  according  to  Mr.  Brande,  from  19  to  25  per  cent, 
of  alcohol,  while  in  the  lighter  wines  of  France  and  Germany  it  sometimes 
falls  as  low  as  12  per  cent.  Strong  ale  contains  about  10  per  cent.,  ordinary 
spirits,  as  brandy,  gin,  whisky,  40  to  50  per  cent.,  or  occasionally  more. 
These  latter  owe  their  characteristic  flavours  to  certain  essential  oils,  present 
in  very  small  quantity,  either  generated  in  the  act  of  fermentation  or  pur- 
posely added. 

In  making  wine,  the  expressed  juice  of  the  grape  is  simply  set  aside  in 
large  vats,  where  it  undergoes  spontaneously  the  necessary  change.  The 
vegetable  albumin  of  the  juice  absorbs  oxygen  from  the  air,  runs  into  decom- 
position, and  in  that  state  becomes  a  ferment  to  the  sugar,  which  is  gradu- 
ally converted  into  alcohol.  If  the  sugar  be  in  excess,  and  the  azotized  mat 
ter  deficient,  the  resulting  wine  remains  sweet ;  but  if,  on  the  other  hand, 
the  proportion  of  sugar  be  small,  and  that  of  albumin  large,  a  dry  wine  is 
produced.  When  the  fermentation  stops,  and  the  liquor  becomes  clear,  it  is 
drawn  oflF  from  the  lees,  and  transferred  to  casks,  to  ripen  and  improve. 

The  colour  of  red  wine  is  derived  from  the  skins  of  the  grapes,  which  in 
such  cases  are  left  in  the  fermenting  liquid.  Effervescent  wines,  as  cham- 
pagne, are  bottled  before  the  fermentation  is  complete ;  the  carbonic  acid  is 
disengaged  under  pressure,  and  retained  in  solution  in  the  liquid.  The  pro- 
cess requires  much  delicate  management. 

During  the  fermentation  of  the  grape-juice,  or  must,  a  crystalline,  stony 
matter,  called  argol,  is  deposited.  This  consists  chiefly  of  acid  tartrate  of 
potassa,  with  a  little  tartrate  of  lime  and  colouring  matter,  and  is  the 
source  of  all  the  tartaric  acid  met  with  in  commerce.  The  salt  in  question 
exists  in  the  juice  in  considerable  quantity ;  it  is  but  sparingly  soluble  in 
water,  but  still  less  so  in  dilute  alcohol ;  hence,  as  the  fermentation  proceeds, 
and  the  quantity  of  spirit  increases,  it  is  slowly  deposited.  The  acid  of  the 
juice  is  thus  removed  as  the  sugar  disappears.  It  is  this  circumstance  which 
renders  grape-juice  alone  fit  for  making  good  wine:  when  that  of  goosebei'- 
ries  or  currants  is  employed  as  a  substitute,  the  malic  and  citric  acids  which 
these  fruits  contain  cannot  be  thus  withdrawn.  There  is,  then,  no  other 
recourse  but  to  add  sugar  in  sufficient  quantity  to  mask  and  conceal  the 
natural  acidity  of  the  liquor.  Such  wines  are  necessarily  acescent,  prone  to 
a  second  fermentation,  and,  to  many  persons,  at  least,  very  unwholesome. 

Beer  is  a  well-known  liquor,  of  great  antiquity,  prepared  from  germinated 
grain,  generally  barley,  and  is  used  in  countries  where  the  vine  does  not 


848  ALCOHOL. 

flourish.  The  operation  of  mailing  is  performed  by  steeping  the  barley  in 
water  until  the  grains  become  swollen  and  soft,  then  piling  it  in  a  heap  or 
couch,  to  favour  the  elevation  of  temperature  caused  by  the  absorption  of 
oxygen  from  the  air,  and  afterwards  spreading  it  upon  a  floor,  and  turning 
it  over  from  time  to  time,  to  prevent  unequal  heating.  When  germination 
has  proceeded  far  enough,  the  vitality  of  the  seed  is  destroyed  by  kiln-dry- 
ing. During  this  process,  the  curious  substance  already  referred  to,  dias- 
tase, is  produced,  and  a  portion  of  the  starch  of  the  grain  converted  into 
sugar,  and  rendered  soluble. 

In  brewing,  the  crushed  malt  is  infused  in  water  at  about  170°  (76°. 6C), 
and  the  mixture  left  to  stand  during  the  space  of  two  hours  or  more.  The 
easily  soluble  diastase  has  thus  an  opportunity  of  acting  upon  the  unaltered 
starch  of  the  grain,  and,  changing  it  into  dextrin  and  sugar.  The  clear 
liquor,  or  wort,  strained  from  the  exhausted  malt,  is  then  pumped  in  a  cop- 
per boiler,  and  boiled  with  the  requisite  quantity  of  hops,  for  communicating 
a  pleasant  bitter  flavour,  and  conferring  on  the  beer  the  property  of  keep- 
ing without  injury.  The  flowers  of  the  hop  contain  a  bitter,  resinous  prin- 
ciple, called  lupulin,  and  an  essential  oil,  both  of  which  are  useful. 

When  the  wort  has  been  sufficiently  boiled,  it  is  drawn  from  the  copper, 
and  cooled,  as  rapidly  as  possible,  to  near  the  ordinary  temperature  of  the 
air,  in  order  to  avoid  an  irregular  acid  fermentation,  to  which  it  would  oth- 
erwise be  liable.  It  is  then  transferred  to  the  fermenting  vessels,  which  in 
large  breweries  are  of  great  capacity,  and  mixed  with  a  quantity  of  yeast, 
the  product  of  a  preceding  operation,  by  which  the  change  is  speedily  in- 
duced. This  is  the  most  critical  part  of  the  whole  operation,  and  one  in 
which  the  skill  and  judgment  of  the  brewer  are  most  called  into  play.  The 
process  is  in  some  measure  under  control  by  attention  to  the  temperature  of 
the  liquid,  and  the  extent  to  which  the  change  has  been  carried  is  easily 
known  by  the  diminished  density,  or  attenuation,  of  the  wort.  The  fermenta- 
tion is  never  sufi^ered  to  run  its  full  course,  but  is  always  stopped  at  a  par- 
ticular point,  by  separating  the  yeast,  and  drawing  ofl^  the  beer  into  casks. 
A  slow  and  almost  insensible  fermentation  succeeds,  which  in  time  renders 
the  beer  stronger  and  less  sweet  than  when  new,  and  charges  it  with  carbonic 
acid. 

Highly  coloured  beer  is  made  by  adding  to  the  malt  a  small  quantity  of 
strongly  dried  or  charred  malt,  the  sugar  of  which  has  been  changed  to  cara- 
mel ;  porter  and  stout  are  so  prepared. 

The  yeast  of  beer  is  a  very  remarkable  substance,  and  has  excited  much 
attention.  To  the  naked  eye  it  is  a  greyish-yellow  soft  solid,  nearly  insoluble 
in  water,  and  dries  up  to  a  pale  brownish  mass,  which  readily  putrefies  when 
moistened,  and  becomes  ofi^ensive.  Under  the  microscope  it  exhibits  a  kind 
of  organized  appearance,being  made  up  of  little  transparent  globules,  which 
sometimes  coliere  in  clusters  or  strings,  like  some  of  the  lowest  members  of 
the  vegetable  kingdom.  Whatever  may  be  the  real  nature  of  the  substance, 
no  doubt  can  exist  that  it  is  formed  from  the  soluble  azotized  portion  of  the 
grain  during  the  fermentive  process.  No  yeast  is  ever  produced  in  liquids 
free  from  azotized  matter ;  that  added  for  the  purpose  of  exciting  fermenta- 
tion in  pure  sugar  is  destroyed,  and  rendered  inert  thereby.  When  yeast  is 
deprived,  by  straining  and  strong  pressure,  of  as  much  water  as  possible,  it 
may  be  kept  in  a  cool  place,  with  unaltered  properties,  for  a  long  time ;  oth- 
erwise, it  speedily  spoils. 

The  dxStiller,  who  prepares  spirits  from  grain,  makes  his  wort,  or  wash, 
much  in  the  same  manner  as  the  brewer ;  he  uses,  however,  with  the  malt  a 
large  quantity  of  raw  grain,  the  starch  of  which  sufi"ers  conversion  into  sugar 
by  toe  diastase  of  the  malt,  which  is  sufficient  for  his  purpose.  He  does  not 
boil  his  infusion  with  hops,  but  proceeds  at  once  to  the  fermentation,  which 


LACTIC     ACID.  849 

he  pushes  as  far  as  possible  by  large  and  repeated  doses  of  yeast.  Alcohol 
is  manufactured  iu  many  cases  from  potatoes ;  the  potatoes  are  ground  to 
pulp,  mixed  with  hot  water  and  a  little  malt,  to  furnish  diastase,  made  to 
ferment,  and  then  the  fluid  portion  distilled.  The  potato-spirit  is  contami- 
nated by  a  very  offensive  volatile  oil,  again  to  be  mentioned ;  the  crude  pro- 
duct from  corn  contains  a  substance  of  a  similar  kind.  The  business  of  the 
rectifier  consists  in  removing  or  modifying  these  volatile  oils,  and  in  replacing 
them  by  others  of  a  more  agreeable  character. 

In  making  bread,  the  vinous  fei'raentation  plays  an  important  part ;  th 
yeast  added  to  the  dough  converts  the  small  portion  of  sugar  the  meal  natu 
rally  contains  into  alcohol  and  carbonic  acid.  The  gas  thus  disengaged 
forces  the  tough  and  adhesive  materials  into  bubbles,  which  are  still  farther 
expanded  by  the  heat  of  the  oven,  which  at  the  same  time  dissipates  the 
alcohol ;  hence  the  light  and  spongy  texture  of  all  good  bread.  Sometimes 
carbonate  of  ammonia  is  employed  with  the  same  view,  being  completely 
volatilized  by  the  high  temperature  of  the  oven.  Bread  is  now  sometimes 
made  by  mixing  a  little  hydrochloric  and  carbonate  of  soda  in  the  dough ;  if 
proper  proportions  be  taken,  and  the  whole  throughly  mixed,  the  operation 
appears  to  be  very  successful.  The  use  of  leaven  is  one  of  great  antiquity ; 
this  is  merely  dough  in  a  state  of  incipient  putrefaction.  When  mixed  with 
a  large  quantity  of  fresh  dough,  it  excites  in  the  latter  the  alcoholic  fermenta- 
tion, in  the  same  manner  as  yeast,  but  less  perfectly ;  it  is  apt  to  communicate 
a  disagreeable  sour  taste  and  odour. 

Lactic  acid  ;  lactic  acid  fermentation  ;  butyhic  acid  fermentation. 
— Azotized  albuminous  substances,  which  in  an  advanced  state  of  putrefactive 
change  act  as  alcohol-ferments,  often  possess,  at  certain  periods  of  decay,  the 
property  of  inducing  an  acid  /fermentation  in  sugar,  the  consequence  of  which 
is  the  conversion  of  that  substance  into  lactic  acid.  Thus,  the  azotized  matter 
of  malt,  when  suffered  to  putrefy  in  water  for  a  few  days,  acquires  the  power 
of  acidifying  the  sugar  which  accompanies  it,  while  in  a  more  advanced  state 
of  decomposition  it  converts,  under  similar  circumstances,  the  sugar  into 
alcohol.  The  glutin  of  grain  behaves  in  the  same  manner:  wheat  flour,  made 
into  a  paste  with  water,  and  left  four  or  five  days  in  a  warm  situation,  be- 
comes a  true  lactic  acid  ferment ;  if  left  a  day  or  two  longer,  it  changes  its 
character,  and  then  acts  like  common  yeast.  Moist  animal  membranes,  in  a 
slightly  decaying  condition,  often  act  energetically  in  developing  lactic  acid. 
Cane-sugar,  probably  by  previously  becoming  grape-sugar,  and  the  sugar 
of  milk,  both  yield  lactic  acid,  the  latter,  however,  most  readily,  the  grape- 
sugar  having  a  strong  tendency  towards  the  alcoholic  change.  A  good  method 
of  preparing  lactic  acid  is  the  following.  An  additional  quantity  of  milk- 
sugar  is  dissolved  in  ordinary  milk,  which  is  then  set  aside  in  a  warm  place, 
until  it  becomes  sour  and  coagulated.  The  casein  of  the  milk  absorbs  oxygen 
from  the  air,  runs  into  putrefaction,  and  acidifies  a  portion  of  the  sugar. 
The  lactic  acid  formed,  after  a  time  coagulates  and  renders  insoluble  the 
casein,  and  the  production  of  that  acid  ceases.  By  carefully  neutralizing, 
however,  the  free  acid  by  carbonate  of  soda,  the  casein  becomes  soluble, 
and,  resuming  its  activity,  changes  a  fresh  quantity  of  sugar  into  lactic  acid, 
which  may  be  also  neutralized,  and  by  a  suflficient  number  of  repetitions  of 
this  process  all  the  sugar  of  milk  present  may,  in  time,  be  acidified.  When 
this  has  taken  place,  the  liquid  is  boiled,  filtered,  and  evaporated  to  dryness 
in  a  water-bath.  The  residue  is  treated  with  hot  alcohol,  which  dissolves  out 
the  lactate  of  soda.  The  alcoholic  solution  may  then  be  decompohed  by  tho 
cautious  addition  of  sulphuric  acid,  which  precipitates  sulphate  rf  soda,  inso- 
luble in  spirit.  The  free  acid  may,  if  needful,  be  neutralized  with  lime,  and 
tne  resultia?  nit  purified  by  re-crystallization  and  the  use  of  animal  char- 
coal, after  wh,fh  it  may  be  decomposed  by  oxalic  aoid 


350  LACTIC    ACID. 

The  following  process  will  be  found  more  economical  on  a  large  scale :  — 
A  mixture  is  made  of  two  gallons  of  milk,  which  may  be  stale  or  skimmed 
milk,  six  pounds  of  raw  sugar,  twelve  pints  of  water,  eight  ounces  of  putrid 
cheese,  and  four  pounds  of  chalk,  which  should  be  mixed  up  to  a  creamy 
consistence  with  some  of  the  liquid.  This  mixture  is  exposed  in  a  loosely- 
covered  jar  to  a  temperature  of  about  86°  (30°C),  with  occasional  stirring. 
At  the  end  of  two  or  three  weeks  it  will  be  found  converted  into  a  semi-solid 
mass  or  pudding  of  lactate  of  lime,  which  may  be  drained,  pressed,  and 
purified  by  re-crystallization  from  water. 

The  lactate  of  lime  may  be  decomposed  by  the  necessary  quantity  of  pure 
oxalic  acid,  the  filtered  liquor  neutralized  with  carbonate  of  zinc,  and,  after 
a  second  filtration,  evaporated  until  the  zinc-salt  crystallizes  out  on  cooling. 
The  latter  may,  lastly,  be  re-dissolved  in  water,  and  decomposed  by  sul- 
phuretted hydrogen,  in  order  to  obtain  the  free  acid. 

If  in  the  first  part  of  the  process  the  solid  lactate  of  lime  be  not  removed 
at  the  proper  period  from  the  fermenting  liquid,  it  will  gradually  re-dissolve 
and  disappear.  On  examination  the  liquid  v^U  then  be  found  to  consist 
chiefly  of  a  solution  of  butyrate  of  lime. 

This  second  stage  of  the  process,  to  which  the  name  of  butyric  acid  fer- 
mentation has  been  given,  is  attended  with  an  evolution  of  hydrogen  and 
carbonic  acid.  It  will  be  mentioned  more  in  detail  in  the  Section  on  Oils 
and  Fats. 

Lactic  acid  may  be  extracted  from  a  great  variety  of  liquids  containing 
decomposing  organic  matter,  as  sauerkraut,  a  preparation  of  white  cabbage ; 
the  sour  liquor  of  the  starch-maker,  &c.  It  has  been  supposed  to  exist  in 
the  blood,  urine,  and  other  animal  fluids ;  recent  researches  have,  however, 
failed  to  detect  it  in  either  blood  or  urine,  although  it  has  been  shown  by 
'  Liebig  to  exist  in  considerable  quantity  in  the  juice  of  flesh  or  muscle. 

Lactic  acid  has  been  lately  produced  artificially  in  a  most  remarkable 
manner  by  the  action  of  nitrous  acid  upon  alanine.  (See  the  Section  on 
Organic  Bases.) 

Solution  of  lactic  acid  may  be  concentrated  in  the  vacuum  of  the  air- 
pump,  over  a  surface  of  oil  of  vitriol,  until  it  acquires  the  aspect  of  a  colour- 
less, syrupy  liquid,  of  sp.  gr.  1-215.  It  has  an  intensely  sour  taste  and 
acid  reaction ;  it  is  hygroscopic,  and  very  soluble  in  water,  alcohol,  and 
ether.  It  forms  soluble  salts  with  all  the  metallic  oxides.  The  syrupy  acid 
contains  CgHgOg-j-HO,  or  C,2HjqO,o-|-2HO,  the  water  being  basic,  and 
su|ceptible  of  replacement  by  a  metallic  oxide. 

'vhen  syrupy  lactic  acid  is  heated  in  a  retort  to  266°  (130°C),  water  con- 
taining a  little  actio  acid  distils  over,  and  the  residue  on  cooling  forms  a  yel- 
lowish solid  fusible  mass,  very  bitter,  and  nearly  insoluble  in  water.  This  is 
anhydrous  lactic  acid,  CgHgOg.  Long-continued  boiling  with  water  converts 
it  into  ordinary  lactic  acid.  When  this  substance  is  farther  heated  it  decom- 
poses, yielding  numerous  products.  One  of  these  is  lactide,  formerly  errone- 
ously called  anhydrous  lactic  acid,  a  volatile  substance,  crystallizing  in 
brilliant  colourless  rhombic  plates,  which,  when  put  into  water,  slowly  dis- 
solve, with  production  of  common  lactic  acid.  Lactide  contains  CgH404 ;  it 
combines  with  ammonia,  forming  lactamide,  CgH7N04,  a  colourless,  crystalli- 
zable,  soluble  substance,  resembling  in  its  chemical  relations  oxamide. 
Another  product  of  the  action  of  heat  on  lactic  acid  is  lactone,  a  colourless 
volatile  liquid,  boiling  at  198°  (92° -20.)  Acetone  is  also  formed,  and  carbonic 
oxide  and  carbonic  acid  are  disengaged. 

A  salt  of  lactic  acid,  gently  heated  with  five  or  six  parts  of  oil  of  vitriol, 
yields  an  enormous  quantity  of  perfectly  pure  carbonic  oxide  gas. 

The  most  important  and  characteristic  of  the  lactates  are  those  of  lime  and 
the  oxide  of  zinc. 


ETHER.  351 

Lactate  of  lime,  CaO.CgHsOg-f-^IIO,  exists  ready-formed,  to  a  small  ex- 
tent, in  Nux  vomica.  When  pure,  it  crystallizes  in  tufts  of  minute  white 
needles  grouped  in  concentric  layers.  It  dissolves  in  10  parts  of  cold,  and 
indefinitely  in  boiling  water,  molting  in  its  water  of  crystallization  at  that 
temperature. 

Lactate  of  zinc,  ZnOjCgHgOg-f-^HO,  is  deposited  from  a  hot  solution  in 
small  brilliant  4-sided  prismatic  ci'ystals,  which  require  for  solution  68  parts 
of  cold  and  6  of  boiling  water. 

Lactate  of  protoxide  of  iron,  FeOjCgHgOg-j-SHO,  is  now  used  in  medi- 
cine. It  is  prepared  by  adding  alcohol  to  a  mixture  of  lactate  of  ammonia 
and  protochloride  of  iron,  when  the  salt  is  precipitated  in  the  form  of  small 
yellowish  needles. 

When  the  expressed  juice  of  the  beet  is  exposed  to  a  temperature  of  90°' 
(32° -90)  or  100<i  (37°-7C)  for  a  considerable  time,  the  sugar  it  contains 
suffers  a  peculiar  kind  of  fermentation,  to  which  the  term  viscous  has  been 
applied.  Gases  are  evolved  which  contain  hydrogen,  and  when  the  change 
appears  complete,  and  the  products  come  to  be  examined,  the  sugar  is  found 
to  have  disappeared.  Mere  traces  of  alcohol  are  produced,  but,  in  place  of 
that  substance,  a  quantity  of  lactic  acid,  mannite,  and  a  mucilaginous  sub- 
stance resembling  gum- Arabic,  and  said  to  be  identical  with  gum  in  com- 
position. 

Pure  sugar  can  be  converted  into  this  substance ;  by  boiling  yeast  or  the 
glutin  of  wheat  in  water,  dissolving  sugar  in  the  filtered  solution,  and  ex- 
posing it  to  a  tolerably  high  temperature,  the  viscous  fermentation  is  set  up, 
and  a  large  quantity  of  the  gummy  principle  generated.  A  little  gas  is  at 
the  same  time  disengaged,  which  is  a  mixture  of  carbonic  acid  and  hydrogen. 


products  of  the  action  of  acids  on  alcohol. 

Ether;  oxide  of  ethyl. — When  equal  weights  of  rectified  spirit  and  oil 
of  vitriol  are  mixed  in  a  retort,  the  latter  connected  with  a  good  condensing 
arrangement,  and  the  liquid  heated  to  ebullition,  a  colourless  and  highly  vo- 
latile liquid,  long  known  under  the  name  of  ether,  or  sulphuric  ether,  distils 
over.  The  process  must  be  stopped  as  soon  as  the  contents  of  the  retort 
blacken  and  froth,  otherwise  the  product  will  be  contaminated  with  other 
substances,  which  then  make  their  appearance.  The  ether  obtained  may  be 
mixed  with  a  little  caustic  potassa,  and  re-distilled  by  a  very  gentle  heat. 

Piire  ether  is  a  colourless,  transparent,  fragrant  liquid,  very  thin  and  mo- 
bile. Its  sp.  gr.  at  60°  (15°-5C)  is  about  0-720;  it  boils  at  96°  (35°-5C) 
under  the  pressure  of  the  atmosphere,  and  bears  without  freezing  the  se- 
verest cold.  When  dropped  on  the  hand  it  occasions  a  sharp  sensation  of 
cold,  from  its  rapid  volatilization.  Ether  is  very  combustible ;  it  burns  with 
a  white  flame,  generating  water  and  carbonic  acid.  Although  the  substance 
itself  is  one  of  the  lightest  of  liquids,  its  vapour  is  very  heavy,  having  a 
density  of  2-586.  Mixed  with  oxygen  gas,  and  fired  by  the  electric  spark, 
or  otherwise,  it  explodes  with  the  utmost  violence.  Preserved  in  an  imper- 
fectly-stopped vessel,  ether  absorbs  oxygen,  and  becomes  acid  from  the  pro- 
duction of  acetic  acid ;  this  attraction  for  oxygen  is  increased  by  elevation 
of  temperature.  It  is  decomposed  by  transmission  through  a  red-hot  tube 
into  olefiant  gas,  light  carbonett^d  hydrogen,  and  a  substance  yet  to  be  de- 
scribed, aldehyde. 


3S2  COMPOUND    ETHERS. 

Etlier  is  miscible  with  alcohol  in  all  proportions,  but  not  with  water ;  it 
dissolves  to  a  small  extent  in  that  liquid,  10  parts  of  water  taking  up  1  part, 
or  thereabouts,  of  ether.  It  may  be  separated  from  alcohol,  provided  the 
quantity  of  the  latter  be  not  excessive,  by  an  addition  of  water,  and  in  this 
manner  samples  of  commercial  ether  may  be  conveniently  examined.  Ether 
is  a  solvent  for  oily  and  fatty  substances  generally,  and  phosphorus  to  a 
small  extent,  a  few  saline  compounds  and  some  organic  principles,  but  its 
powers  in  this  respect  are  much  more  limited  than  those  of  alcohol  or  water. 

Ether  was  the  first  part  of  a  great  number  of  analogous  substances  in 
"which  the  property  of  producing  temporary  insensibility  to  pain  was  recog- 
nized. In  surgical  operations,  the  use  of  ether  is  now  superseded  by  that 
of  chloroform. 

Ether  is  found  by  analysis  to  contain  C4H5O ;  it,  therefore,  differs  from  al- 
cohol, C4Hg02,  by  the  elements  of  water.  Alcohol  is  often  regarded  as  the 
hydrate  of  ether;  but  as  ether  cannot  be  made  to  combine  with  water  di- 
rectly, and  as  alcohol  cannot  be  converted  into  ether  by  the  abstraction  of 
water  by  the  aid  of  substances  known  to  possess  a  high  affinity  for  that  body, 
such  a  view  was  always  looked  upon  as  hypothetical.  Recent  experiments 
have,  in  fact,  shown  that  a  very  different  relation  exists  between  alcohol  and 
ether.  We  shall  return  to  these  researches,  when  we  consider  the  theory  of 
the  production  of  ether,  which  will  be  discussed  partly  in  connection  with 
the  history  of  sulphovinic  acid,  and  partly  with  that  of  the  methyl-com- 
pounds. 

Compound  ethers  ;  ethyl-theory  ;  ethyl.  —  The  so-called  compound 
etliers  constitute  a  vei'y  large  and  important  class  of  substances  derived 
from  alcohol,  and  containing  either  the  elements  of  ether,  in  combination 
with  those  of  an  oxygen-acid,  inorganic  or  organic,  or  the  elements  of  de- 
fiant gas  in  union  with  those  of  a  hydrogen-acid.  The  relations  of  these 
compounds  to  alcohol  and  the  acids  are  most  simply  and  clearly  illustrated 
by  comparing  them  with  ordinary  salts,  in  which  the  metal  is  replaced  by  a 
salt-basyle  termed  ethyl,  containing  C4H5.  This  substance  forms  haloid-salts 
by  combining  with  chlorine,  iodine,  bromine,  &c.,  and  its  oxide,  identical  or 
isomeric  with  common  ether,  with  oxygen-acids,  like  basic  metallic  oxides  in 
general.  A  body  containing  carbon  and  hydrogen  in  the  proportions  indi- 
cated by  the  formula  C4H5,  has  been  lately  obtained  by  Dr.  Frankland,  from 
one  of  the  members  of  this  group  of  compounds,  and  describe''  under  the 
name  of  ethyl.  It  is  formed  by  exposing  iodide  of  ethyl  in  sealed  tubes,  to 
the  action  of  metallic  zinc,  at  a  temperature  of  320°  (160°C).'  In  this  re- 
action, the  iodine  of  the  iodide  of  ethyl  C4H5I  combines  with  the  zinc,  and 
ethyl  is  set  free.  On  opening  the  sealed  tubes,  and  allowing  the  gas,  which 
is  ethyl  mixed  with  several  secondary  products  (especially  defiant  gas),  to 
pass  into  a  freezing  mixture,  the  temperature  of  which  is  kept  below — 9° 
( — 23°C),  the  ethyl  condenses  to  a  colourless  mobile  liquid.  It  is  not  at- 
tacked by  concentrated  sulphuric  and  nitric  acids.  Chlorine  acts  upon  it 
under  the  influence  of  light,  but  not  in  the  dark.  Hitherto  no  compound 
ether  has  been  reproduced  from  ethyl.  The  ethyl-theory,  proposed  by  the 
sagacity  of  Liebig  long  before  the  separation  of  ethyl  itself,  will  be  found 
highly  useful  as  an  aid  to  the  memory ;  it  must  not,  however,  be  forgotten 
that  the  compound  ethers  are  distinguished  by  important  characters  from 
real  and  undoubted  salts. 

Table  of  Ethyl- Compounds. 

Ethyl,  symbol  Ae C4Hg 

Oxide  of  ethyl ;  ether C4H6O 

Hydrate  of  the  oxide ;  alcohol C4H60,H0 

»  See  also,  zino-ethyl,  page  368. 


COMPOUND     ETHERS.  863 

Chloride  of  ethyl C^HgCl 

Bromide  of  ethyl C4H5Br 

Iodide  of  ethyl C4H5I 

Cyanide  of  ethyl C4H5Cy 

Nitrate  of  oxide  of  ethyl C4H50,N05 

Nitrite  of  oxide  of  ethyl C4H50,N03 

Oxalate  of  oxide  of  ethyl C4H50,Cg03 

Hydride  of  ethyl C4H5H 

Zinc-ethyl C4H5Zn 

&c.  &c. 

The  ethers  of  many  of  the  acids  may  be  formed  by  the  direct  action  of 
these  latter  upon  alcohol  at  a  high  temperature,  the  elements  of  water  being 
displaced  by  those  of  the  acid ;  this  is  chiefly  conspicuous  with  the  volatile 
acids.  A  more  ready  general  method  of  forming  them,  however,  is  to  distil 
a  mixture  of  alcohol,  sulphuric  acid,  and  a  salt  of  the  acid  the  ether  of  which 
is  required.  The  fatty  acids,  which  in  general  cannot  be  distilled  without 
more  or  less  decomposition,  yield  their  ethers  with  great  facility  by  the  action 
of  hydrochloric  acid  gas  upon  an  alcoholic  solution  of  the  acid. 

The  compound  ethers  are  mostly  volatile  aromatic  liquids,  in  a  few  cases 
crystallizable  solids,  without  action  on  vegetable  colours,  sparingly  soluble 
in  water,  but  dissolved  in  all  proportions  by  alcohol  and  ether.  They  are 
not  acted  upon  in  the  cold  by  alkaline  carbonates,  but  suflFer  decomposition 
with  more  or  less  difficulty  when  heated  with  aqueous  solutions  of  caustic 
alkali,  a  salt  of  the  acid  of  the  ether  being  usually  generated,  and  alcohol 
formed  and  set  free.  An  alcoholic  solution  of  hydrate  of  potassa  or  soda  is 
more  active  in  this  respect.  The  same  kind  of  decomposition  is  often 
brought  about  by  the  prolonged  contact  of  boiling  water. 

Chloride  of  ethyl  ;  light  hydrochloric  ether  ;  AeCl.  —  Rectified 
spirit  of  wine  is  saturated  with  dry  hydrochloric  acid  gas,  and  the  product 
distilled  with  very  gentle  heat;  or  a  mixture  of  3  parts  oil  of  vitriol  and  2 
of  alcohol  is  poured  upon  4  parts  of  dry  common  salt  in  a  retort,  and  heat 
applied;  in  either  case  the  vapour  of  the  hydrochloric  ether  should  be  con- 
ducted through  a  little  tepid  water  in  a  wash-bottle,  and  then  conveyed  Into 
a  small  receiver  surrounded  by  ice  and  salt.  It  is  purified  from  adhering 
water  by  contact  with  a  few  fragments  of  fusecJ  chloride  of  calcium.  Hy- 
drochloric ether  is  a  thin,  colourless,  and  excessively  volatile  liquid,  of  a 
penetrating,  aromatic,  and  somewhat  alliaceous  odour.  At  the  freezing  point 
of  water,  its  sp.  gr.  is  0-921,  and  it  boils  at  50°  (12°-5C) ;  it  is  soluble  in  10 
parts  of  water,  is  not  decomposed  by  solution  of  nitrate  of  silver,  but  is 
quickly  resolved  into  chloride  of  potassium  and  alcohol  by  a  hot  solution  of 
caustic  potassa. 

Bromide  of  ethyl;  hydrobromio  ether;  AeBr. — This  is  prepared  by 
distilling  a  mixture  of  8  parts  bromine,  1  part  phosphorus,  and  32  parts 
alcohol.  The  phosphorus  is  converted  into  phosphorous  acid  by  the  oxygen 
of  the  alcohol,  when  the  ethyl  combines  with  the  bromine ;  3  equivalents  of 
alcohol,  3  equivalents  of  bromine,  and  1  equivalent  of  phosphorus,  yield  3 
equivalents  of  bromide  of  ethyl,  3  equivalents  of  water,  and  1  equivalent  of 
phophorous  acid.  It  is  a  very  volatile  liquid,  boiling  at  10U°  (41  °C),  of 
penetrating  taste  and  smell,  and  superior  in  density  to  water. 

Iodide  of  ethyl;  hydriodig  ether;  Ael. — Obtained  by  gradually  mix- 
ing, with  precaution,  1  part  of  phosphorus,  5  parts  of  alcohol,  and  10  parts 
of  iodine  (1  eq.  of  phosphorus,  3  eq.  of  alcohol,  and  3  eq.  of  iodine),  and 
distilling.  The  reaction  is  analagous  to  that  described  in  the  case  of'  the 
bromide.  Iodide  of  ethyl  is  a  colourless  liquid,  of  penetrating  and  ethereal 
odour,  having  a  density  of  1-92,  and  boiling  at  158°  (70"C).  It  b-^comes  reU 
30* 


354 


COMPOUND    ETHERS. 


by  contact  with  air  from  a  commencement  of  decomposition.  This  Bubstance 
has  become  highly  important  as  a  source  of  ethyl,  and  from  its  remarkable 
deportment  with  ammonia,  which  will  be  discussed  in  the  Section  on  Organic 
Bases. 

Sulphide  of  ethyl  ;  AeS. — Formed  by  the  action  of  chloride  of  ethyl 
upon  a  solution  of  the  protosulphate  of  potassium.  It  is  colourless,  has  a 
disagreeable  garlic  odour,  and  boils  at  180°  (82°C). 

Cyanide  op  ethyl,  AeCy. — This  is  produced  when  a  mixture  of  sulphovi- 
nate  of  potassa  and  cyanide  of  potassium,  both  in  a  dry  state,  is  slowly 
heated.  It  is  colourless,  when  perfectly  pure  it  has  a  powerful,  not  disa- 
greeable odour,  and  a  sp.  gr.  of  0-788.  It  boils  at  190°-4  (88°C).  This 
substance  has  lately  been  studied  by  Drs.  Kolbe  and  Frankland.  They  have 
found  that  cyanide  of  ethyl  differs  from  the  ordinary  ethers  in  its  deportment 
with  the  alkalis.  Instead  of  yielding  cyanide  of  potassium  and  alcohol,  it  is 
converted  into  ammonia  and  propionic  acid,  CjHgOj.HO,  a  peculiar  acid 
closely  allied  to  acetic  acid,  and  which  will  be  noticed  more  in  detail  under 
the  head  of  acetone.  Cyanide  of  ethyl,  in  this  reaction,  absorbs  4  equiva- 
lents of  water : — 


1  eq.  of  propionic  acid CgHg    O^ 

1  eq.  of  ammonia HgN 


1  eq.  of  cyanide  of  ethyl....  CgHjN 
4  eq.  of  water H^  O4 

CgH.NO, 

(See  cyanide  of  methyl.) — When  acted  upon  by  potassium,  cyanide  of  ethyl 
furnishes  a  gas,  the  nature  of  which  is  not  definitely  settled ;  the  residue 
contains  cyanide  of  potassium  and  an  organic  alkali  cyanethine,  which  coii- 
tains  CigHisNj,  and  is  formed  by  the  coalescence  of  three  equivalents  of  the 
cyanide. 

Sulphite  op  oxide  op  ethyl;  sulphurous  ether  ;  AeO,S02. — This  sub- 
stance was  obtained  by  adding  absolute  alcohol  in  excess  to  subchloride  of 
sulphur.  Hydrochloric  acid  is  evolved,  and  sulphur  deposited,  while  the 
sulphite  of  ethyl  distils  as  a  limpid  strongly  smelling  liquid,  of  sp.  gr.  1-085, 
boiling  at  338°  (170°C),  it  is  slowly  decomposed  by  water. 

Sulphate  OF  oxide  OP  ethyl;  sulphuric  ether;  AeOjSOg.  —  This  sub- 
stance has  been  only  recently  obtained.  It  is  formed  by  passing  the  vapour 
of  anhydrous  sulphuric  acid  into  perfectly  anhydrous  ether.  A  syrupy  liquid 
is  produced,  which  is  shaken  with  4  vols,  of  water  and  1  vol.  of  ether,  when 
two  layers  are  formed;  the  lower  contains  sulphovinic  acid,  and  various  other 
compounds,  while  the  upper  layer  consists  of  an  ethereal  solution  of  sul- 
phate of  ethyl.  At  a  gentle  heat  the  ether  is  volatilized,  and  the  sulphate 
of  ethyl  remains  as  a  colourless  liquid.  It  cannot  be  distilled  without  decom- 
position. 

Phosphate  of  oxide  of  ethyl  ;  phosphoric  ether.  —  See  phosphovinic 
acid. 

Nitrate  op  oxide  op  ethyl;  nitric  ether;  AeO.NOg.  —  The  nitrate 
likewise  has  only  recently  been  obtained  ;  it  is  prepared  by  cautiously  dis- 
tilling a  mixture  of  equal  weights  of  alcohol  and  moderately  strong  nitric 
acid,  to  which  a  small  quantity  of  nitrate  of  urea  has  been  added.  The  ac- 
tion of  nitric  acid  upon  alcohol  is  peculiar;  the  facility  with  which  that  acid 
is  deoxidized  by  combustible  bodies,  leads,  under  ordinary  circumstances,  to 
the  production  of  nitrous  acid  on  the  one  hand,  and  an  oxidized  product  of 
alcohol  on  the  other,  a  nitrite  of  the  oxide  of  ethyl  being  generated  instead 
of  a  nitrate.  M.  Millon  has  shown  that  the  addition  of  urea,  from  reasons 
to  be  explained  when  this  compound  will  be  described,  entirely  prevents  the 
formation  of  that  substance,  and  at  the  same  time  preserves  the  alcohol  from 
oxidation  by  undergoing  that  change  in  its  place,  the  sole  liquid  product 


COMPOUND    ETHERS.  855 

being  the  new  ether.  The  experiment  is  most  safely  conducted  on  a  small 
scale,  and  the  distillation  must  be  stopped  when  seven-eighths  of  the  whole 
have  passed  over ;  a  little  water  added  to  the  distilled  product  separates  the 
nitric  ether.  Nitric  ether  has  a  density  of  1-112;  it  is  insoluble  in  water, 
has  an  agreeable  sweet  taste  and  odour ;  and  is  not  decomposed  by  an  aque- 
ous solution  of  caustic  potassa,  although  that  substance  dissolved  in  alcohol 
attacks  it  even  in  the  cold,  with  production  of  nitrate  of  potassa.  Its  vapoui 
is  apt  to  explode  when  strongly  heated. 

Nitrite  of  oxide  of  ethyl;  nitrous  ether;  AeOjNOg. — Pure  nitrous 
ether  can  only  be  obtained  by  the  direct  action  of  the  acid  itself  upon  alcohol. 
1  part  of  potato-starch,  and  10  parts  of  nitric  acid,  are  gently  heated  in 
a  capacious  retort  or  flask,  and  the  vapour  of  nitrous  acid  thereby  evolved 
conducted  into  alcohol  mixed  with  half  its  weight  of  water,  contained  in  a 
two-necked  bottle,  which  is  to  be  plunged  into  cold  water,  and  connected  with 
a  good  condensing  arrangement.  All  elevation  of  temperature  must  be  care- 
fully avoided.  The  product  of  this  operation  is  a  pale  yellow  volatile  liquid, 
possessing  an  exceedingly  agreeable  odour  of  apples  ;  it  boils  at  62°  (16°'6C), 
and  has  a  density  of  0-947.  It  is  decomposed  by  potassa,  without  darkening, 
into  the  nitrite  of  the  base,  and  alcohol. 

Nitrous  ether,  but  contaminated  with  aldehyde,  may  be  prepared  by  the 
following  simple  method :  —  Into  a  tall  cylindrical  bottle  or  jar  are  to  be 
introd-aced  successively  9  parts  of  alcohol  of  sp.  gr.  0-830,  4  parts  of  water, 
and  8  parts  of  strong  fuming  nitric  acid  ;  the  two  latter  are  added  by  means 
of  a  long  funnel  with  very  narrow  orifice,  reaching  to  the  bottom  of  the  bottle, 
so  that  the  contents  may  form  three  distinct  strata,  which  slowly  mix 
from  the  solution  of  the  liquids  in  each  other.  The  bottle  is  then  lojsely 
stopped,  and  left  two  or  three  days  in  a  cool  place,  after  which  it  is  found  to 
contain  two  layers  of  liquids,  of  which  the  uppermost  is  the  ether.  It  is  puri- 
fied by  rectification.  A  somewhat  similar  product  may  be  obtained  by  care- 
fully distilling  a  mixture  of  3  parts  rectified  spirit  and  2  of  nitric  acid  of  1  -28 
sp.  gi\  ;  the  fire  must  be  withdrawn  as  soon  as  the  liquid  boils. 

The  sweet  spirits  of  nitre  of  pharmacy,  prepared  by  distilling  three  pounds 
of  alcohol  with  four  ounces  of  nitric  acid,  is  a  solution  of  nitrous  ether,  alde- 
hyde, and  perhaps  other  substances,  in  spirit  of  wine. 

Carbonate  OF  oxide  OF  ETHYL  ;  carbonic  ether  ;  AeOjCOg.  —  Fragments 
of  potassium  or  sodium  are  dropped  into  oxalic  ether  as  long  as  gas  is  disen- 
gaged ;  the  brown  pasty  product  is  then  mixed  with  water  and  distilled.  The 
carbonic  ether  is  found  floating  upon  the  surface  of  the  water  of  the  receiver 
as  a  colourless,  limpid  liquid  of  aromatic  odour  and  burning  taste.  It  boils 
at  259°  (126°C),  and  is  decomposed  by  an  alcoholic  solution  of  potassa  into 
carbonate  of  that  base  and  alcohol.  The  reaction  which  gives  rise  to  this 
substance  is  unexplained. 

Silicic  and  boracic  ethers.  —  A  number  of  these  compounds  appear  tvi 
exist,  containing  different  proportions  of  the  acids.  Silicic  ether,  containing 
SAeOjSiOa,  was  obtained  by  M.  Ebelmen  by  the  action  of  anhydrous  alcohol 
upon  chloride  of  silicium.  It  is  a  colourless,  limpid,  aromatic  liquid,  of  sp. 
gr,  0-933,  boiling  at  329°  (165oC),  and  decomposed  by  water  with  production 
of  silicic  acid  and  alcohol.  In  contact  with  moist  air  it  is  gradually  resolved 
into  translucent  hydrate  of  silica,  which  becomes  in  the  end  hard  enough  to 
scratch  glass.  By  substituting  ordinary  spirit  for  absolute  alcohol,  other 
compounds  containing  a  larger  portion  of  silicic  acid  are  obtained. 

Boracic  ether  was  procured  by  a  similar  process,  substituting  the  chloride 
of  boron  for  chloride  of  silicium.  It  formed  a  thin,  limpid  liquid  of  agreeable 
odour,  having  the  sp.  gr,  of  0-885,  and  boiling  at  246°  (118°C),  It  is  decom- 
posed by  water.  Its  alcoholic  solution  burns  with  a  fine  green  flame,  throw 
ing  oflF  a  thick  smoke  of  boracic  acid.     It  contains  3AeO,BoO,.     A  aecoml 


S56  COMPOUND    ETHERS. 

boracic  ether  in  the  form  of  a  solid  glassy  fusible  substance,  containing 
AeO,2Bo03,  was  formed  by  the  action  of  fused  boracic  acid  upon  absolute 
alcohol.  It  is  volatile  in  the  vapour  of  alcohol  only,  and  is  decomposed  by 
"water. 

Of  the  ethers  of  the  organic  acids,  the  following  are  the  most  important : — 

Oxalate  of  the  oxide  of  ethyl  ;  oxalic  ether  ;  AeO,C203. — This  com- 
pound is  most  easily  obtained  by  distilling  together  4  parts  binoxalate  of 
potassa,  5  parts  oil  of  vitriol,  and  4  parts  strong  alcohol.  The  distillation 
may  be  pushed  nearly  to  dryness,  and  the  receiver  kept  warm  to  dissipate 
any  ordinary  ether  that  may  be  formed.  The  product  is  mixed  with  water, 
by  which  the  oxalic  ether  is  separated  from  the  undecomposed  spirit ;  it  is 
repeatedly  washed  to  remove  adhering  acid,  and  re-distilled  in  a  small  retort, 
the  first  portions  being  received  apart  and  rejected.  Another  very  simple 
process  consists  in  digesting  equal  parts  of  alcohol  and  dehydrated  oxalic 
acid,  in  a  flask  furnished  with  a  long  glass  tube,  in  which  the  volatilized  spirit 
may  condense.  After  6  or  8  hours'  digestion,  the  mixture  generally  contains 
only  traces  of  oxalic  acid  which  is  not  etherified. 

Pure  oxalic  ether  is  a  colourless,  oily  liquid,  of  pleasant  aromatic  odour, 
and  1-09  sp.  gr.  It  boils  at  363°  (183°-8C)  is  but  little  soluble  in  water, 
and  is  readily  decomposed  by  caustic  alkalis  into  an  oxalate  and  alcohol. 
With  solution  of  ammonia  in  excess,  it  yields  oxamide  and  alcohol.  C4H5O, 
CjOg-f  NH3=C202,NH2-|-C4H50,HO.  This  is  the  best  process  for  preparing 
oxamide,  which  is  obtained  perfectly  white  and  pure.  (See  page  343.)  When 
dry  gaseous  ammonia  is  conducted  into  a  vessel  containing  oxalic  ether,  the 
gas  is  rapidly  absorbed,  and  a  white  solid  substance  produced,  which  is  so- 
luble in  hot  alcohol,  and  separates,  on  cooling,  in  colourless,  transparent, 
scaly  crystals.  They  dissolve  in  water,  and  are  both  fusible  and  volatile. 
The  name  oxamethane  is  given  to  this  body ;  it  consists  of  CgH7NOg=C4H50, 
C4H2NO5,  i.  e.,  the  ether  of  oxamic  acid  (see  page  343).  The  same  substance 
is  formed  when  ammonia  in  small  quantity  is  added  to  a  solution  of  oxalic 
ether  in  alcohol. 

When  oxalic  ether  is  treated  with  dry  chlorine  in  excess  in  the  sunshine, 
a  white,  colourless,  crystalline,  fusible  body  is  produced,  insoluble  in  water 
and  instantly  decomposed  by  alcohol.  It  contains  CgCl504,  or  oxalic  ether 
in  which  the  whole  of  the  hydrogen  is  replaced  by  chlorine. 

Acetate  of  oxide  of  ethyl;  acetic  ether;  AeO,C4H303. — Acetic  ether 
is  conveniently  made  by  heating  together  in  a  retort  3  parts  of  acetate  of 
potassa,  3  parts  of  strong  alcohol,  and  2  of  oil  of  vitriol.  The  distilled  pro- 
duct is  mixed  with  water,  to  separate  the  alcohol,  digested  first  with  a  little 
chalk,  and  afterwards  with  fused  chloride  of  calcium,  and,  lastly,  rectified. 
The  pure  ether  is  an  exceedingly  fragrant,  limpid  liquid ;  it  has  a  density  of 
0-890,  and  boils  at  165°  (73°-8C).  Alkalis  decompose  it  in  the  usual  manner. 
When  treated  with  ammonia,  it  yields  acetamide,  a  crystalline  substance 
soluble  in  water  and  alcohol,  which  contains  C4H5N02=C4H302,NH2,  i.  e., 
acetate  of  ammonia — 2  equivalents  of  water.  Its  formation  is  analogous  to 
that  of  oxamide.  Alkalis  and  acids  reconvert  it  into  ammonia  and  acetic 
acid.  When  treated  with  nitrous  acid,  it  yields  acetic  acid,  water  and  ni- 
trogen gas,  C4H5N02-f  N03=C4H303,HO+HO-f  2N. 

Formate  of  the  oxide  of  ethyl;  formic  ether;  AeO,C2H03. — A  mix- 
ture of  7  parts  of  dry  formate  of  soda,  10  of  oil  of  vitriol,  and  6  of  strong 
alcohol,  is  to  be  subjected  to  distillation.  The  formic  ether,  separated  by 
the  addition  of  water  to  the  distilled  product,  is  agitated  with  a  little  mag- 
nesia, and  left  several  days  in  contact  with  chloride  of  calcium.  Foi'mic 
ether  is  colourless,  has  an  aromatic  smell,  and  density  of  0-915,  and  boils  at 
138°  (56^C).     Watei  diss/lves  this  substance  to  a  small  extent. 


COMPOUND    ETHERS.  857 

The  ethers  of  many  of  the  vegetable  acids  have  been  obtained  and  de- 
scribed. 

The  ethers  of  cyanic  and  cyanuric  acids  have  been  formed  and  studied. 
The  description  of  these  remarkable  substances  and  of  their  important  pro- 
ducts of  decomposition  is  postponed  until  the  history  of  the  acids  themselves 
has  been  given. 

Ethers  of  the  fatty  acids. — Normal  stearic  ether  has  not  yet  been  ob- 
tained. By  passing  hydrochloric  acid  gas  into  an  alcoholic  solution  of  stearic 
acid,  Redtenbacher  succeeded  in  obtaining  the  compound  AeO,HO,Ce3Hg605' 
It  resembled  white  wax,  was  inodorous  and  tasteless,  melted  at  86°  (30°C), 
and  could  not  be  distilled  without  decomposition.  It  was  readily  decomposed 
by  boiling  with  caustic  alkalis.  Margaric  ether  is  prepared  by  a  similar  mode 
of  proceeding.  When  purified  from  excess  of  acid  by  agitation  with  succes- 
sive small  quantities  of  weak  spirit,  and  afterwards  made  to  crystallize 
slowly  from  the  same  menstruum,  it  forms  regular,  brilliant,  colourless  crys- 
tals, fusible  at  70°  (2lo-lC),  and  distilling  without  decomposition  ;  when  less 
pure  it  is  in  great  part  destroyed  by  this  latter  proceiSS.  Margaric  ether 
contains  AeO,C34A3303.  An  oleic  ether,  and  corresponding  compounds  of  seve- 
ral other  less  important  fatty  acids,  have  been  formed  and  described.  They 
greatly  resemble  each  other  in  characters. 

Butyric  and  valerianic  ethers,  AeOjCgH^Og,  and  AeOjCjoHgOg.  —  The 
ether-compounds  of  these  acids  are  easily  obtained  by  the  preceding  process. 
They  are  fragrant  volatile  liquids,  having  an  odour  resembling  that  of  the 
rind  of  the  pine-apple.  They  are  used  for  flavouring  brandy.  They  are 
lighter  than  water,  boil  at  a  high  temperature,  and  possess  the  constitution 
and  general  character  of  the  class  of  bodies  to  which  they  belong. 

(Enanthic  ether.  —  The  aroma  possessed  by  certain  wines  appears  due  to 
the  presence  of  the  ether  of  a  peculiar  acid  called  oenanthic,  and  which  is  pro- 
bably generated  during  fermentation.  When  such  wines  are  distilled  on  the 
large  scale,  an  oily  liquid  passes  over  towards  the  close  of  the  operation, 
which  consists,  in  great  measure,  of  the  crude  ether ;  it  may  be  purified  by 
agitation  with  solution  of  carbonate  of  potassa,  freed  from  water  by  a  few 
fragments  of  chloride  of  calcium,  and  re-distilled.  (Enanthic  ether  is  a  thin, 
colourless  liquid,  having  a  powerful  and  almost  intoxicating  vinous  odour ; 
it  has  a  density  of  0-862,  boils  at  482°  (2.50°C),  and  is  but  sparingly  soluble 
in  water,  although,  like  the  compound  ethers  in  general,  it  dissolves  with 
facility  in  alcohol.     It  contains  C22H]204,  or  AeO.CjgHj^O,. 

A  hot  solution  of  caustic  potassa  instantly  decomposes  oenanthic  ether ; 
alcohol  distils  over,  and  oenanthate  of  potassa  remains  in  the  retort;  the 
latter  is  readily  decomposed  by  warm  dilute  sulphuric  acid,  with  liberation  of 
oenanthic  acid.  Purified  by  repeated  washing  with  hot  water,  cenanthic  acid 
presents  the  appearance  of  a  colourless,  inodorous  oil,  which  at  77°  (25°C) 
becomes  a  soft  solid,  like  butter.  It  reddens  litmus  paper,  and  dissolves 
easily  in  solutions  of  the  alkaline  carbonates  and  in  spirit,  and  very  much 
resembles  the  fatty  acids,  to  be  hereafter  described,  the  products  of  saponi- 
fication. The  acid  thus  obtained  is  a  hydrate,  composed  of  CigHi^Os+HO. 
An  acid  of  exactly  the  same  composition  has  been  obtained  from  Pelargonium 
roseum,  and  described  by  the  name  of  pelargonic  acid.  It  is  likewise  pro- 
duced, together  with  a  host  of  similar  acids,  by  the  action  of  nitric  acid  upon 
oleic  acid.  (Enanthic  ether  may  be  reproduced  by  distilling  a  mixture  of  6 
parts  sulphovinate  of  potassa,  and  1  part  hydrated  oenanthic  acid,  or  perhaps 
better,  by  the  ordinary  process  for  the  ethers  of  the  fatty  acids. 

Chlgrocarbonic  ether.  —  Although  the  constitution  of  this  suDstance  is 
doubtful,  it  may  be  here  described.  Absolute  alcohol  is  introduced  into  ft 
glass-globe  containing  chlorocarbonic  acid  (phosgene  gas,  p.  131) ;  the  gas  is 
absorbed  in  large  quantity,  and  a  yellowish  liquid  produced,  from  whioh 


358  COMPOUND    ACIDS    CONTAINING 

water  separates  the  chlorocarbonic  ether.  When  freed  from  water  by  chlo- 
ride of  calcium,  and  from  adhering  acid  by  rectification  from  litharge,  it  forms 
a  thin,  colourless,  neutral  liquid,  which  burns  with  a  green  flame.  Its  den- 
sity is  1-133  ;  it  boils  at  202°  (94" -SC).  The  vapour,  mixed  with  a  large  quan- 
tity of  air,  has  an  agreeable  odour,  but  when  nearly  pure  is  extremely  suffo- 
cating. It  contains  CgH5C104=C4H50,C2C108.  The  density  of  the  vapour 
is  3-82. 

The  action  of  ammonia,  gaseous  or  liquid,  upon  this  substance,  gives  rise 
to  a  very  curious  product,  called  by-  M.  Dumas  urethane ;  sal-ammoniac  is 
at  the  same  time  formed.  Urethane  is  a  white,  solid,  crystallizable  body, 
fusible  below  212°  (100°C),  and  distilling  unchanged,  when  in  a  dry  state,  at 
about  356°  (180°C) ;  if  moisture  be  present,  it  is  decomposed,  with  evolution 
of  ammonia.  Water  dissolves  this  substance  very  easily  ;  the  solution  is  not 
affected  by  nitrate  of  silver,  and  yields,  by  spontaneous  evaporation,  large 
and  distinct  crystals.  It  contains  CgIl7N04,  or  elements  of  carbonic  ether 
V  and  ureay — whence  tlie  name. 


COMPOUND  ACIDS  CONTAINING  THE  ELEMENTS  OF  ETHER. 

SuLPHOviNic  ACID,  C4H50,2S03,HO.  —  Strong  rectified  spirit  of  wine  is 
mixed  with  a  double  weight  of  concentrated  sulphuric  acid ;  the  mixture  is 
heated  to  its  boiling  point,  and  then  left  to  cool.  When  cold,  it  is  diluted 
with  a  large  quantity  of  water,  and  neutralized  with  chalk ;  much  sulphate 
of  lime  is  produced.  The  latter  is  placed  upon  a  cloth  filter,  drained,  and 
pressed ;  the  clear  solution  is  evaporated  to  a  small  bulk  by  the  heat  of  a 
water-bath,  filtered  from  a  little  sulphate,  and  left  to  crystallize ;  the  pro- 
duct is  sulphotnnate  of  lime,  in  beautiful  coloui-less,  transparent  crystals,  con- 
taining CaO,C4H50,2S03-f-2HO.  They  dissolve  in  an  equal  weight  of  cold 
water,  and  efiloresce  in  a  dry  atmosphere. 

A  similar  salt,  containing  baryta,  BaO,C4H50,2S03-f-2HO,  equally  soluble, 
and  still  more  beautiful,  may  be  produced  by  substituting,  in  the  above  pro- 
cess, carbonate  of  bai-yta  for  chalk ;  from  this  substance  the  hydrated  acid 
may  be  procured  by  exactly  precipitating  the  base  by  dilute  sulphuric  acid, 
and  evaporating  the  filtered  solution,  in  vacuo,  at  the  temperature  of  the  air. 
It  forms  a  sour  syrupy  liquid,  in  which  sulphuric  acid  cannot  be  recognized, 
and  is  very  easily  decomposed  by  heat,  and  even  by  long  exposure  in  the 
vacuum  of  the  air-pump.  All  the  sulphovinates  are  soluble  ;  the  solutions 
are  decomposed  by  ebullition.  The  lead-salt  resembles  the  barytic  com- 
pound. That  of  potassa,  easily  made  by  decomposing  sulphovinate  of  lime 
by  carbonate  of  potassa,  is  anhydrous ;  it  is  permanent  in  the  air,  very  solu- 
ble, and  crystallizes  well. 

Sulphovinate  of  potassa,  distilled  with  concentrated  sulphuric  acid,  gives 
ether ;  with  dilute  sulphuric  acid,  alcohol ;  and  with  strong  acetic  acid,  acetic 
ether.  Heated  with  hydrate  of  lime  or  baryta,  the  sulphovinates  yield  a  sul- 
phate of  the  base  and  alcohol. 

Phosphovinic  ACID,  C4H50,P05,2HO.  — This  acid  is  bibasic.  The  baryta- 
salt  is  prepared  by  heating  to  180°  (82-°2C)  a  mixture  of  equal  weights  of 
strong  alcohol  and  syrupy  phosphoric  acid,  diluting  this  mixture,  after  the 
lapse  of  24  hours,  with  water,  and  neutralizing  by  carbonate  of  baryta.  The 
solution  of  phosphovinate,  separated  by  filtration  from  the  insoluble  phos- 
phate, is  evaporated  at  a  moderate  temperature.  The  salt  crystallizes  in  bril- 
liant hexagonal  plates,  which  have  a  pearly  lustre,  and  are  more  soluble  in 
eold  than  in  hot  water ;  it  dissolves  in  15  parts  of  water  at  68°  (20°C).    The 


THE  ELEMENTS  OP  ETHER.  359 

crystals  contains  2BaO,C4H50,P054-12HO.  From  this  substance  the  hydra- 
ted  acid  may  be  obtained  by  precipitating  the  baryta  by  dilute  sulphuric  acid, 
and  evaporating  the  filtered  liquid  in  the  vacuum  of  the  air-pump ;  it  forms 
a  coloui'less,  syrupy  liquid,  of  intensely  sour  taste,  which  sometimes  exhibits 
appearances  of  crystallization.  It  is  very  soluble  in  water,  alcohol,  and 
ether,  and  easily  decomposed  by  heat  when  in  a  concentrated  state.  The 
phosphovinates  of  lime,  silver,  and  lead  possesses  but  little  solubility ;  those 
of  the  alkalis,  magnesia,  and  strontia  are  freely  soluble. 

Voegeli  has  lately  observed  that,  by  the  action  of  syrupy  phosphoric  acid 
upon  alcohol,  together  with  phosphovinic  acid,  another  acid  is  formed,  to 
which  he  gives  the  name  phosphobiethylic  acid,  phosphovinic  acid  being 
designated  by  phosphethylic  acid.  The  baryta  silver  and  lead-salt  of  this 
acid  are  more  soluble  than  the  corresponding  phosphovinates.  The  lead- 
salts  aud  lime-salts  are  anhydrous,  and  contain  respectively  PbO,2C4H50,P05 
and  CaO,2C4H50,P05. 

The  former  of  these  salts,  when  heated  to  a  temperature  between  356° 
and  374°  (180°  and  190°C),  yields  an  aromatic,  limpid  liquid,  which  is 
tribasic  phosphoric  ether,  3C4H50,P05.  It  boils  at  288°-5  (142°-5C).  Its 
formation  is  represented  by  the  equation :  2(PbO,2C4H50,P05)=z=3C4H50,POj 
4.2PbO,C4H50,P05. 

OxALOViNic  Acid,  €41150,20203.  HO. — Oxalic  ether  is  dissolved  in  anhy- 
drous alcohol,  and  enough  alcoholic  solution  of  caustic  potassa  added  to 
neutralize  one-half  of  the  oxalic  acid  present,  whereupon  the  potassa-salt  of 
the  new  acid  precipitates  in  the  form  of  crystalline  scales,  insoluble  in 
alcohol,  but  easily  dissolved  by  water.  The  free  acid  is  obtained  as  a  sour 
and  exceedingly  instable  liquid  by  the  addition  of  hydrofluosilicic  acid  to  a 
solution  of  the  preceding  salt  in  dilute  alcohol.  It  forms  with  baryta  a 
very  soluble  salt. 

A  tartrovinic  acid  has  been  described,  and  many  other  compounds  of  the 
same  type  exist. 


Another,  and  a  diflFerent  view,  is  very  frequently  taken  of  the  substances 
just  described,  and  of  many  analogous  compounds.  The  sulphovinates, 
phosphovinates,  &c.,  are  supposed  to  possess  a  constitution  resembling  that 
of  ordinary  double  salts,  one  of  the  bases  being  a  metallic  oxide,  and  the 
second  ether.  Thus,  anhydrous  sulphovinate  of  baryta  is  written  BaO,SOs 
-f-C4H50,S03,  or  double  sulphate  of  baryta  and  ether  ;  hydrated  sulphovinic 
acid  is  HO,  803-4-041150,803,  or  bisulphate  of  ether.  There  are,  however, 
grave  objections  against  this  mode  of  viewing  the  subject:  in  every  true 
double  salt  the  characters  both  of  acid  and  bases  remain  unchanged ;  alum 
gives  the  reactions  of  sulphuric  acid,  of  alumina,  and  of  potassa ;  while  in 
sulphovinic  acid  or  sulphovinate  not  a  trace  of  sulphuric  acid  can  be 
detected  by  any  method  short  ef  actual  decomposition,  by  heat  or  otherwise. 
If  sulphovinate  of  baryta  contain  sulphate  of  baryta  ready  formed,  it  is 
very  difficult  to  understand  how  that  salt  can  be  decomposed  by  an  addition 
of  sulphuric  acid.  The  student  must,  however,  bear  in  mind  that  all  views 
of  the  constitution  of  complex  organic  compounds  must,  of  necessity,  be  to 
a  great  extent  hypothetical,  and  liable  to  constant  alteration  with  the 
progress  of  science. 


Products  of  the  Decomposition  of  Sulphovinic  Acid  by  Heat. 

A  solution  of  sulphovinic  acid,  or,  what  is  equivalent  to  it,  a  mixture,  m 
due  proportions,  of  oil  of  vitriol  and  strong  alcohol,  undergoes  decomposi- 
tion  when  heated,  yielding  products  which  differ  with  the  temperature  to 


560  C0MP0UN1>    ACIDS    CONTAINING 

■which  the  liquid  is  subjected.  The  cause  of  the  decomposition  is  to  bt 
traced  to  the  instability  of  the  compound  itself,  and  to  the  basic  power  of 
•water,  and  the  attraction  of  sulphuric  acid  for  the  latter,  in  virtue  of  which 
it  determines  the  production  of  that  substance,  and  liberates  the  elements 
of  the  ether. 

When  the  sulphovinic  acid  is  so  far  diluted  as  to  boil  at  260°  (126° -60  or 
below,  or  when  a  temperature  not  exceeding  this  is  applied  to  a  stronger 
solution  by  the  aid  of  a  liquid  bath,  the  compound  acid  is  resolved  into  sul- 
phuric acid,  which  remains  behind  in  the  retort  or  distillatory  vessel,  while 
alcohol,  and  mere  traces  of  ether,  are  volatilized. 

An  acid  whose  boiling-point  lies  between  260°  and  310°  (126-6  and 
154° -SC)  is  decomposed  by  ebullition  into  hydrated  sulphuric  acid  and 
ether,  which  is  accompanied  by  small  quantities  of  alcohol. 

Lastly,  when,  by  the  addition  of  a  large  quantity  of  oil  of  vitriol,  the 
boiling-point  of  the  mixture  is  made  to  rise  to  320°  (160°C)  and  above,  the 
production  of  ether  diminishes,  and  other  substances  begin  to  make  their 
appearance,  of  which  the  most  remarkable  is  defiant  gas.  The  mixture  in 
the  retort  blackens,  sulphurous  acid  and  carbonic  acid  are  disengaged,  a 
yellow,  oily  aromatic  liquid  passes  over,  and  a  coaly  residue  is  left,  which 
contains  sulphur.  The  chief  and  characteristic  product  is  the  defiant  gas ; 
the  others  may  be  considered  the  result  of  secondary  actions.  The  three 
modes  of  decomposition  may  be  thus  contrasted : — 

Below  260°— C4H50,2S03,HO+2HO  =  C4H50,H0-f  2(S03,H0) 
260°— 310°— C4H50,2S03,HO-f  HO  =  C.HgO  -f  2(S03,HO) 
Above  320°— C4H60,2S03,H0  =   C4H4  -f-^lSOa.HO) 

The  ether-producing  temperature  is  thus  seen  to  be  circumscribed  within 
narrow  limits;  in  the  old  process,  however,  in  which  a  mixture  of  equal 
■weights  of  alcohol  and  sulphuric  acid  is  subjected  to  distillation,  these  con- 
ditions can  be  but  partially  complied  with.  At  first  the  temperature  of  the 
mixture  is  too  low  to  yield  ether  in  any  quantity,  and  towards  the  end  of  the 
process,  long  before  all  the  suphovinic  acid  has  been  decomposed,  it  becomes 
too  high,  so  that  defiant  gas  and  its  accompanying  products  appear  instead. 
The  remedy  to  this  inconvenience  consists  in  restraining  the  temperature  of 
ebullition  of  the  mixture  within  its  proper  bounds  by  the  introduction  of  a 
constant  supply  of  alcohol,  to  combine  with  the  liberated  sulphuric  acid,  and 
reproduce  the  sulphovinic  acid  as  fast  as  it  becomes  destroyed.  The  im- 
proved, or  continuous  ether-process,  in  which  the  same  acid  is  made  to  ethe- 
rify  an  almost  indefinite  quantity  of  spirit,  may  be  thus  elegantly  conducted 
upon  a  small  scale. 

A  wide-necked  flask  is  fitted  with  a  sound  cork,  perforated  by  three  aper- 
tures, one  of  which  is  destined  to  receive  a  thermometer,  with  the  graduation 
on  the  stem ;  a  second,  the  vertical  portion  of  a  long  narrow  tube,  termina- 
ting in  an  orifice  of  about  J^  of  an  inch  in  diameter ;  and  the  third,  a  wide 
bent  tube,  connected  with  me  condenser,  to  carry  ofi"  the  volatile  products. 
A  mixture  is  made  of  8  parts  by  weight  of  concentrated  sulphuric  acid,  and 
5  parts  of  rectified  spirit  of  wine,  of  about  0-834  sp.  gr.  This  is  introduced 
into  the  flask,  and  heated  by  a  lamp.  The  liquid  soon  boils,  and  the  ther- 
mometer very  shortly  indicates  a  temperature  of  300°  (149°C) ;  when  this 
happens,  alcohol  of  the  above  density  is  suffered  slowly  to  enter  by  the 
narrow  tube,  which  is  put  in  communication  with  a  reservoir  of  that  liquid, 
consisting  of  a  large  bottle  perforated  by  a  hole  near  the  bottom,  and  fur- 
nished with  a  small  brass  stop-cock,  fitted  by  a  cork ;  the  stop-cock  is  secured 
to  the  end  of  the  long  tube  by  a  caoutchouc  connecter,  tied,  as  usual  with 
silk  cord.  As  the  tube  passes  nearly  to  the  bottom  of  the  flask,  the  alcohol 
gets  thoroughly  mixed  with  the  acid  liquid,  the  hydrostatic  pressure  of  the 


IHE    ELEMENTS     OF   ETHER. 
Pig.  166.* 


361 


fluid  column  being  sufficient  to  ensure  the  regularity  of  the  flow ;  the  quan- 
tity is  easily  adjusted  by  the  aid  of  the  stop-cock.  For  condensation,  a 
Liebig's  condenser  may  be  used,  supplied  with  ice-water.  The  arrangement 
is  figured  above  (fig.  166). 

The  intensity  of  heat,  and  the  supply  of  alcohol,  must  be  so  adjusted  that 
the  thermometer  may  remain  at  300°  (149°C),  or  as  near  that  temperature 
as  possible,  while  the  contents  of  the  flask  are  maintained  in  a  state  of  rapd 
and  violent  ebullition — a  point  of  essential  importance.  Ether  and  water 
distil  over  together,  and  collect  in  the  receiver,  forming  two  distinct  strata  ; 
the  mixture  slowly  blackens,  from  some  slight  secondary  action  of  the  acid 
upon  the  spirit,  or  upon  the  impurities  in  the  latter,  but  retains,  after  many 
hours'  ebullition,  its  etherifying  powers  unimpaired.  The  acid,  however, 
slowly  volatilizes,  partly  in  the  state  of  oil  of  wine,  and  the  quantity  of  liquid 
in  the  flask  is  found,  after  the  lapse  of  a  considerable  interval,  sensibly 
diminished.  This  loss  of  acid  constitutes  the  only  limit  to  the  duration  of 
the  process,  which  might  otherwise  continue  indefinitely. 

On  the  large  scale,  the  flask  may  be  replaced  by  a  vessel  of  lead,  the  tubes 

«  Fig.  166.    Apparatus  for  the  preparation  of  ether,    a.  Flask  containing  the  mixture  of  oil 
of  Titriol  and  alcohol,    b.  Reservoir  with  stop-cock,  for  supplying  a  constant  stream  of  alcchol 
c.  Wide  bent  tube  connected  with  the  condenser  for  convejing  away  the  vapours-    d.  Th« 
thermometer  for  regulating  the  temperature  of  the  boiling  liquid. 
31 


862  OLEFIANT    GAS. 

being  also  of  the  same  metal ;  the  stem  of  the  thermometer  may  be  made  ta 
pass  air-tight  through  the  cover,  and  heat  may,  perhaps,  be  advantageously 
applied  by  high-pressure  steam,  or  hot  oil,  circulating  in  a  spiral  of  metal 
tube,  immersed  in  the  mixture  of  acid  and  spirit. 

The  crude  ether  is  to  be  separated  from  the  water  on  which  it  floats,  agi- 
tated with  a  little  solution  of  caustic  potassa,  and  re-distilled  by  the  heat  of 
warm  water.  The  aqueous  portion,  treated  with  an  alkaline  solution,  and 
distilled,  yields  alcohol,  containing  a  little  ether.  Sometimes  the  spontaneous 
separation  before  mentioned  does  not  occur,  from  the  accidental  presence  of 
a  larger  quantity  than  usual  of  undecomposed  alcohol ;  the  addition  of  a  little 
water,  however,  always  suffices  to  determine  it. 

We  shall  once  more  return  to  the  formation  of  ether,  when  we  discuss  the 
methyl-compounds. 

Heavy  oil  of  wine, — When  a  mixture  of  2^  parts  of  concentrated  sulphu- 
ric acid,  and  1  part  of  rectified  spirit  of  wine,  of  0-833  sp.  gr.,  is  subjected 
to  distillation,  a  little  ether  comes  over,  but  is  quickly  succeeded  by  a  yel- 
lowish, oily  liquid,  which  may  be  freed  from  sulphurous  acid  by  agitation 
with  water,  and  from  ether  and  undecomposed  alcohol  by  exposure  in  the 
vacuum  of  the  air-pump,  beside  two  open  capsules,  the  one  containing  hy- 
drate of  potassa,  and  the  other  concentrated  sulphuric  acid.  This  substance 
may  be  prepared  in  larger  quantity  by  the  destructive  distillation  of  dry  sul- 
phoviuate  of  lime ;  alcohol,  oil  of  wine,  and  a  small  quantity  of  an  exceed- 
ingly volatile  liquid,  yet  imperfectly  examined,  are  produced.  Pure  oil  of 
wine  is  colourless,  or  greenish,  of  oily  consistence,  and  heavier  than  water ; 
it  has  an  aromatic  taste,  and  an  odour  resembling  that  of  peppermint.  Its 
boiling  point  is  tolerably  high.  It  is  soluble  in  alcohol  and  ether,  but 
scarcely  so  in  water.  By  analysis  it  is  found  to  contain  C8HgO,2S03,  or  per- 
haps 04114.803-1-041150,803;  that  is,  neutral  sulphate  of  ether,  in  combina- 
tion with  the  sulphate  of  a  hydro-carbon,  etherole. 

In  contact  with  boiling  water,  oil  of  wine  is  resolved  into  sulphovinic  acid, 
and  a  volatile  liquid,  known  by  the  name  of  light,  or  siveet  oil  of  wine;  with 
an  alkaline  solution,  this  effect  is  produced  even  with  greater  facility.  Light 
oil  of  wine,  left  in  a  cool  place  for  several  days,  deposits  crystals  of  a  white 
solid  matter,  which  is  tasteless,  and  has  but  little  odour ;  it  is  called  etherin. 
The  fluid  residual  portion  is  yellowish,  oily,  and  lighter  than  water ;  it  has 
a  high  boiling-point,  solidifies  at  a  very  low  temperature,  and  is  freely  soluble 
in  alcohol  and  ether;  it  bears  the  name  of  etherole.  Both  etherole  and  etherin 
have  the  same  composition,  namely  C^H^,  and  are  consequently  isomeric  with 
defiant  gas. 

Olefiant  gas  ;  ethyline.  —  This  substance  may  also  be  advantageously 
prepared  on  the  principle  described,  by  restraining  the  temperature  within 
certain  bounds,  and  preventing  the  charring  and  destruction  of  the  alcohol, 
which  alwfiys  occurs  in  the  old  process,  and  which,  at  the  same  time,  leads 
to  the  production  of  sulphurous  and  carbonic  acids,  which  contaminate 
the  gas. 

If  the  vapour  of  alcohol  be  passed  into  somewhat  diluted  sulphuric  acid, 
maintained  at  a  boiling-heat,  it  is  absorbed  with  production  of  sulphovinic 
acid,  which  is  shortly  afterwards  decomposed  into  water  and  olefiant  gas. 
The  process  is  thus  conducted : — A  wide-necked  flask  (fig.  167),  containing 
rectified  spirit  of  wine,  is  fitted  with  a  cork,  throiigh  which  pass  an  ordinary 
safety-tube,  with  a  little  water,  and  the  bent  glass  tube,  intended  to  convey 
the  vapour  of  the  spirit  into  the  acid.  The  latter  must  be  of  such  strength, 
as  to  have  a  boiling-point  between  320°  and  330=  (160°  and  165° -.50) ;  it  is 
prepared  by  diluting  strong  oil  of  vitriol  with  rather  less  than  half  its  weight 
of  water.  The  acid  is  placed  in  a  second  and  larger  flask,  also  closed  by  a 
cork,  into  which  are  inserted  two  tubes  and  a  thermometer.     The  first  is  * 


DUTCH-Ll  3UTD. 
Fig.  167. 


363 


Fig.  168. 


piece  of  straight  tube,  wide  enough  to  allow  the  tube  conveying  the  alcohol- 
vapour  to  pass  freely  down  it,  and  dipping  a  little  way  into  the  acid ;  the 
second  is  a  narrow  bent  tube,  the  extremity  of  which  is  immersed  in  the 
water  of  the  pneumatic  trough.  Both  flasks  are 
heated  ;  and  as  soon  as  it  is  seen  that  the  acid  is  in  a 
state  of  tranquil  ebullition,  while  the  thermometer 
marks  the  temperature  above  mentioned,  the  spirit  is 
made  to  boil,  and  its  vapour  carried  into  the  acid, 
which  very  soon  begins  to  evolve  defiant  gas  and 
vapour  of  water,  accompanied  by  a  little  ether  and  oil 
of  wine,  but  no  sulphurous  acid.  The  acid  liquid  does 
not  blacken,  and  the  experiment  may  be  carried  on  as 
long  as  may  be  desired.  This  is  a  very  elegant  and 
instructive,  although  somewhat  troublesome,  method 
of  preparing  the  gas.  The  essential  parts  of  the 
apparatus  are  shown  in  fig.  167. 

Chloride  op  olefiant  gas  ;  Dutch-liquid. — It 
has  long  been  known  that  when  equal  measures  of 
olefiant  gas  and  chlorine  are  mixed  over  water,  absorp- 
tion of  the  mixture  takes  place,  and  a  yellowish  oily 
liquid  is  produced,  which  collects  upon  the  surface  of 
the  water,  and  ultimately  sinks  to  the  bottom  in  drops. 
It  may  be  easily  prepared,  in  quantity,  by  causing 
the  two  gases  to  combine  in  a  glass  globe,  fig.  168, 
having  a  narrow  neck  at  the  lower  part,  dipping  into 
a  small  bottle,  destined  to  receive  the  product.  The 
two  gases  are  conveyed  by  separate  tubes,  and 
allowed  to  mix  in  the  globe,  the  olefiant  gas  being 


864  CHLORIDES    or    CARBON. 

kept  a  little  in  excess.  The  chlorine  should  be  washed  with  water,  and  the 
defiant  gas  passed  through  strong  oil  of  vitriol,  to  remove  vapour  of  ether ; 
the  presence  of  sulphurous  and  carbonic  acids  is  not  injurious.  Combina- 
tion takes  place  very  rapidly,  and  the  liquid  product  trickles  down  the  sides 
of  the  globe  into  the  receiver.  When  a  considerable  quantity  has  been  col- 
lected, it  is  agitated  first  with  water,  and  afterwards  with  concentrated  sul- 
phui'ic  acid ;  it  is,  lastly,  purified  by  re-distillation.  If  impure  defiant  gas 
be  employed,  the  crude  product  contains  a  large  quantity  of  a  substance 
called  by  M,  Regnault  chloro-sulphuric  acid,  SOgCl,  which,  on  contact  with 
water,  is  converted,  by  the  decomposition  of  the  latter,  into  sulphuric  and 
hydrochloric  acids. 

Pure  Dutch-liquid  is  a  thin,  colourless  liquid,  of  agreeably  fragrant  odour, 

and  sweet  taste ;  it  is  slightly  soluble  in  water,  and  readily  so  in  alcohol  and 

ther.     It  is  heavier  than  water,  and  boils  when  heated  to  180°  (82° -SC) ; 

t  is  unaffected  by  oil  of  vitriol  and  solid  hydrate  of  potassa.     When  in- 

liamed,  it  burns  with  a  greenish,  smoky  light.     This  substance  yields,  by 

ualysis,  C4H4CI2. 

"V^en  Dutch-liquid  is  treated  with  an  alcoholic  solution  of  caustic  potassa, 

is  slowly  resolved  into  chloride  of  potassium,  which  separates,  and  into  a 
■.^  .J  and  exceedingly  volatile  substance,  containing  C4H3CI,  whose  vapour 
.  ^quires  to  be  cooled  down  to  0°  ( — 17°-7C)  before  it  condenses.  At  this 
I-  mperature  it  forms  a  limpid,  colourless  liquid.  Chlorine  is  absorbed  by 
tliis  substance,  and  a  compound  produced,  which  contains  C4H3CI3 ;  this  is 
in  turn  decomposed  by  an  alcoholic  solution  of  hydrate  of  potassa  into 
chloride  of  potassium  and  a  new  volatile  liquid,  C4H2CI2. 

Bromide  and  iodide  of  olefiant  gas,  C4H4Br2  and  C4H4I2. — These 
compounds  correspond  to  Dutch-liquid ;  they  are  produced  by  bringing 
olefiant  gas  in  contact  with  bromine  and  iodine.  The  bromide  is  a  colour- 
less liquid,  of  agreeable,  ethereal  odour,  and  has  a  density  of  2-16;  it  boils 
at  265°  (129°-5C),  and  solidifies,  when  cooled,  to  near  0°  (— 17°-7C).  The 
iodide  is  a  colourless,  crystalline,  volatile  substance,  of  penetrating  odour ; 
it  melts  at  174°  (78°-8C),  resists  the  action  of  sulphuric  acid,  but  is  decom- 
posed by  caustic  potassa. 

Products  of  the  action  of  chlorine  on  dutch-liquid  ;  chlorides 
ov  CARBON. — Dutch-liquid  readily  absorbs  chlorine  gas,  and  yields  several 
new  compounds,  produced  by  the  abstraction  of  successive  portions  of 
hydrogen,  and  its  replacement  or  substitution  by  equivalent  quantities  of 
ciilorine.  This  regular  substitution  of  chlorine,  bromine,  iodine,  &c.,  in 
I'lace  of  hydrogen,  as  before  stated,  is  a  phenomenon  of  constant  occur- 
• '  ice  in  reactions  between  these  bodies  and  very  many  organic  compounds. 
ii  the  present  case  four  such  steps  may  be  traced,  giving  rise,  in  each 
u),-3tance,  to  hydrochloric  acid  and  a  new  substance.  Three  out  of  the  four 
new  products  are  volatile  liquids,  containing  C4HgCl3,C4H2Cl4  and  C4HCI5; 
the  fourth  C4Clg  in  which  the  substitution  of  chlorine  for  hydrogen  is  com- 
plete, is  the  chloride  of  carbon,  long  ago  obtained  by  Mr.  Faraday  by  putting 
Dutch-liquid  into  a  vessel  of  chlorine  gas,  and  exposing  the  whole  to  the 
influence  of  light. 

Sesguichloride  or  Perchloride  of  Carbon,  C4Clg,  is  a  white,  solid,  crystalline 
sul»stance,  of  aromatic  odour,  insoluble  in  water,  but  easily  dissolved  by 
alcohol  and  ether;  it  melts  at  320°  (160°C),  and  boils  at  a  temperature  a 
little  above.  It  burns  with  difficulty,  and  is  unaffected  by  both  acids  and 
alkalis.     It  is  prepared  as  above  stated. 

Frotochloride  of  Carbon,  C4CI4. — When  the  vapour  of  the  preceding  sub- 
stance is  transmitted  through  a  red-hot  porcelain  tube  filled  with  fragments 
of  glass  or  rock-crystal,  it  is  decomposed  into  free  chlorine,  and  a  second 
chloride  of  carbon,  which  condenses  in  the  form  of  a  volatile,  colourlesa 


ETHIONIC    AND    ISET 11  IONIC    ACIDS.  365 

liquid,  which  has  a  density  of  1-55,  and  boils  at  248°  (120<»C).  The  density 
ol  its  vapour  is  5-82.     It  resembles  in  chemical  relations  the  perchloride. 

Subchloride  of  Carbon,  C4CI2,  is  produced  when  the  protochloride  is  passed 
many  successive  times  through  an  ignited  porcelain  tube ;  it  is  a  white, 
volatile,  silky  substance,  soluble  in  ether. 

Bichloride  of  Carbon,  C2CI4. — A  fourth  chloride  of  carbon  is  known  and  will 
be  described  here,  although  it  is  not  derived  from  the  alcohol  group.  It  is 
formed  by  passing  the  vapour  of  bisulphide  of  carbon  together  with  chlo- 
rine, through  a  red-hot  porcelain-tube.  A  mixture  of  chloride  of  sulphur 
and  bichloride  of  carbon  is  formed,  which  is  distilled  with  potassa,  when 
the  chloride  of  sulphur  is  decomposed,  and  pure  bichloride  passes  over.  It 
is  a  colourless  liquid  of  1-56  sp.  gr.,  and  boils  at  170°-6  (77°C).  An  alco- 
holic solution  of  potassa  converts  this  compound  into  a  mixture  of  chloride 
of  potassium  and  carbonate  of  potassa.  The  same  compound  is  formed  by 
exhausting  the  action  of  chlorine  upon  marsh-gas  and  chloride  of  methyl  in 
the  sunshine. 

Combustible  platinum-salts  of  Zeisb. — A  solution  of  bichloride  of  pla- 
tinum in  alcohol  is  mixed  with  a  little  chloride  of  potassium  dissolved  in  hy- 
drochloric acid,  and  the  whole  digested  some  hours  at  a  high  temperature. 
The  alcohol  is  distilled  off,  the  acid  residue  neutralized  by  carbonate  of 
potassa,  and  left  to  crystallize.  The  distilled  liquid  contains  hydrochloric 
ether  and  aldehyde.  The  platinum-salt  forms  yellow,  transparent,  prismatic 
crystals,  which  become  opaque  on  heating  from  loss  of  water  ;  when  intro- 
duced into  the  flame  of  a  spirit  lamp,  the  salt  burns  vividly,  leaving  metallic 
platinum.  It  is  soluble  in  5  parts  of  warm  water.  When  dried  at  212" 
(100°C),  this  substance  contains  Pt2Cl2,C4H4-|-KCl.  Corresponding  com- 
pounds, containing  Pt2Cl2,C4H4-j-NaCl,  and  Pt2Cl2,C4H4-}-NH4Cl,  are  known 
to  exist. 

The  chloride  of  potassium  can  be  separated  from  the  above  compound  by 
the  cautious  addition  of  bichloride  of  platinum ;  the  filtered  solution  yields 
by  evaporation  in  vacuo  a  yellow,  gummy,  acid  mass.  The  solution  is  slowly 
decomposed  in  the  cold,  and  rapidly  at  a  boiling  heat,  with  separation  of  a 
black  precipitate.    These  compounds  are  of  uncertain  constitution. 


PRODUCTS    OF    THE    ACTION    OF    ANHYDROUS    SULPHURIC    ACID    ON    ALCOHOL 
AND    OLEriANT    GAS. 

When  anhydrous  alcohol  is  made  to  absorb  the  vapour  of  anhydrous  sul- 
ohuric  acid,  a  white,  crystalline,  solid  substance  is  produced,  fusible  at  a 
gentle  heat,  which,  when  purified  from  adhering  acid,  is  found  to  consist  of 
carbon,  hydrogen,  and  the  elements  of  sulphuric  acid,  in  the  relation  of  the 
equivalent  numbers,  or  probably  C4H4,4S03.  To  this  substance  Magnus 
applies  the  name  sulphate  of  carbyl.  A  body  very  similar  in  appearance  and 
properties,  and  probably  identical  with  this,  had  previovLsly  been  produced 
by  M.  Regnault,  by  passing  pure  and  dry  olefiant  gas  over  anhydrous  sul- 
phuric acid  contained  in  a  bent  tube. 

When  the  crystals  of  sulphate  of  carbyl  are  dissolved  in  alcohol,  water 
added,  the  whole  neutralized  by  carbonate  of  baryta,  and  the  filtered  solu- 
tion concentrated  by  very  gentle  heat  to  a  small  bulk,  and  then  mixed  with 
a  quantity  of  alcohol,  a  precipitate  falls,  which  consists  of  baryta,  in  com- 
bination with  a  peculiar  acid  closely  resembling  the  sulphovinic,  but  yet 
differing  in  many  important  particulars.  By  the  cautious  addition  of  dilute 
31  « 


366  CHLORAL. 

sulphuric  acid,  the  base  may  be  withdrawn,  and  the  hydrate  of  the  new  acid 
left  in  solution ;  it  bears  the  name  of  ethionic  acid,  and  contains  C4H50,4S0j-f- 
2  HO.  The  ethionates  differ  completely  from  the  sulphovinates ;  all  are  soluble 
in  water,  and  appear  to  be  anhydrous.  Those  of  lime,  baryta,  and  oxide  of 
lead  refuse  to  crystallize ;  the  ethionates  of  potassa,  soda,  and  ammonia,  on 
the  contrary,  may  readily  be  obtained  in  good  crystals. 

When  a  solution  of  ethionic  acid  is  boiled,  it  is  decomposed  into  sulphuric 
acid,  and  a  second  new  acid,  the  isethionic,  isomeric  with  sulphovinic  acid. 
The  isethionic  acid  and  its  salts  are  very  stable :  their  solutions  may  be 
boiled  without  decomposition.  The  isethionates  of  baryta,  lead,  copper, 
potassa,  soda,  and  ammonia  crystallize  with  facility,  and  cannot  be  confounded 
with  the  sulphovinates.     The  hydrated  acid  contains  C4H50,2S03-j-HO. 

The  action  of  anhydrous  sulphuric  acid  on  ether,  as  has  been  already  men- 
tioned, gives  rise  to  the  formation  of  neutral  sulphate  of  ethyl  (see  page  354.) 
Together  with  this  substance  sulphuric  acid  and  several  other  acids  methionic 
and  althionic  are  obtained,  which  are  not  yet  sufficiently  studied. 


PRODUCTS    OF   THE    ACTION    OF    CHLORINE   ON   ALCOHOL,    ETHER,    AND   ITS 
COMPOUNDS. 

Chloral.  —  Perfectly  dry  chlorine  is  passed  into  anhydrous  alcohol  to 
saturation;  the  gas  is  absorbed  in  large  quantity,  and  hydrochloric  acid 
abundantly  produced.  Towards  the  end  of  the  process  the  reaction  must  be 
aided  by  heat.  When  no  more  hydrochloric  acid  appears,  the  current  of 
hlorine  is  interrupted,  and  the  product  agitated  with  three  times  its  volume 
of  concentrated  sulphuric  acid  ;  on  gently  warming  this  mixture  in  a  water- 
bath,  the  impure  chloral  separates  as  an  oily  liquid,  which  floats  on  the 
surface  of  the  acid ;  it  is  purified  by  distillation  from  fresh  oil  of  vitriol,  and 
aftei-wards  from  a  small  quantity  of  quick-lime,  which  must  be  kept  com- 
pletely covered  by  the  liquid,  until  the  end  of  the  operation.  Chloral  has 
:  eea  obtained  from  starch,  by  distillation  with  hydrochloric  acid  and  binoxide 
of  manganese. 

Chloral  is  a  thin,  oily,  colourless  liquid,  of  peculiar  and  penetrating  odour, 
which  excites  tears ;  it  has  but  little  taste.  When  dropped  upon  paper  it 
leaves  a  greasy  stain,  which  is  not,  however,  permanent.  It  has  a  density 
of  1-502,  and  boils  at  20lo-2  (94°C).  Chloral  is  freely  soluble  in  water, 
alcohol,  and  ether  ;  it  forms,  with  a  small  quantity  of  water,  a  solid,  crystal- 
line hydrate ;  the  solution  is  not  affected  by  nitrate  of  silver.  Caustic  baryta 
and  lime  decompose  the  vapour  of  chloral  when  heated  in  it  with  appearance 
of  ignition;  the  oxide  is  converted  into  chloride,  carbon  is  deposited,  and  car- 
bonic oxide  set  free.  Solutions  of  caustic  alkalis  also  decompose  it,  with 
production  of  a  formate  of  the  base,  and  a  new  volatile  liquid,  chloroform. 
Chloral  contains  C4HCI3O2. 

When  chloral  is  preserved  for  any  length  of  time,  even  in  a  vessel  heime- 
tically  sealed,  it  undergoes  a  very  extraordinary  change;  it  becomes  con- 
verted into  a  solid,  white,  translucent  substance,  insoluble  chloral,  possessing 
exactly  the  same  composition  as  the  liquid  itself.  The  new  product  is  but 
very  slightly  soluble  in  water,  alcohol,  or  ether ;  when  exposed  to  heat,  alone 
..r  in  contact  with  oil  of  vitriol,  it  is  re-converted  into  ordinary  chloral.  So- 
lution of  caustic  potassa  resolves  it  into  formic  acid  and  chloroform.  Bro- 
mine acts  upon  alcohol  in  the  same  manner  as  chlorine,  and  gives  rise  to  a 
product  very  similar  in  properties  to  the  foregoing,  called  brumal,  which  con. 


ALCOHOL.  6K)i 

tains  C^HBrgOj.  It  forma  a  crystallizable  hydrate  with  water,  and  is  aecom  • 
posed  by  strong  alkaline  solutions  into  formic  acid  and  bromoform.  A  cor- 
responding iodine-compound  probably  exists.  ♦ 

Chlorine  acts  in  a  diflFerent  manner  upon  alcohol  which  contains  water ; 
when  very  dilute,  the  principal  products  are  hydrochloric  acid  and  aldehyde, 
the  change  being  one  of  oxidation  at  the  expense  of  the  water.  With  strong 
spirit  the  reaction  is  more  complex,  one  of  its  products  being  a  volatile,  oily, 
colourless  liquid,  of  uncertain  composition,  long  known  under  the  name  of 
heavy  muriatic  elher. 

The  mode  of  action  of  dry  chlorine  on  pure  ether  conforms  strictly  to  the 
law  of  substitution  before  mentioned ;  the  carbon  remains  intact,  while  a 
portion  or  the  whole  of  the  hydrogen  is  removed,  and  its  place  supplied  by 
an  e(iuivalent  quantity  of  chlorine.  Ether  exposed  to  a  current  of  the  dry 
gas  for  a  considerable  period,  the  temperature  being  at  first  artifically 
reduced,  yields  a  heavy  oily  product,  having  the  odour  of  fennel.  This  ia 
found  by  analysis  to  contain  C4HgCl30,  or  ether,  in  which  2  eq.  of  chlorine 
have  been  substituted  for  2  eq.  of  hydrogen.  It  may  be  termed  bichlori- 
netted  ether.  By  the  farther  action  of  chlorine,  aided  by  sunlight,  the  re- 
maining hydrogen  is  removed,  and  a  white  crystalline  solid  substance,  closely 
resembling  sesquichloride  of  carbon  produced.  This  is  composed  of  C4CI5O  ; 
it  is  called  pentachlorinetted  ether.  In  a  substance  called  cloretheral, 
C4H4CIO,  accidentally  formed  by  M.  d'Arcet,  in  the  preparation  of  Dutch- 
liquid,  from  the  ether-vapour  mixed  with  the  defiant  gas,  we  have  evidently 
the  first  member  of  this  series. 

With  the  compound  ethers,  the  same  remarkable  law  is  usually  followed. 
The  change  is,  however,  often  complicated  by  the  appearance  of  secondai-y 
products.  Thus,  chlorinetted  acetic  ether,  a  dense,  oily  liquid,  very  different 
from  common  acetic  ether,  was  found  to  contain  C8HgCl204,  being  a  substi- 
tution product  of  CgHg04=  04X150,0411303;  and  chlorinetted  formic  ether, 
0511401204,  is  formed,  in  like  manner,  by  the  substitution  of  2  eq.  chlorine 
for  2  eq.  hydrogen  in  ordinary  formic  ether,  0gHgO4=04H5O,C2HO3.  A 
most  remarkable  and  interesting  set  of  compounds,  due  to  substitution  of 
this  kind,  are  formed  by  the  action  of  chlorine  on  chloride  of  ethyl,  or  light 
hydrochloric  ether.  When  the  vapour  of  this  substance  is  brought  into  con- 
tact with  chlorine  gas,  the  two  bodies  combine  to  a  colourless  oily  liquid, 
very  like  Dutch-liquid,  but  yet  differing  from  it  in  several  important  points  ; 
it  has,  however,  precisely  the  same  composition,  and  its  vapour  has  the  same 
density.  By  the  prolonged  action  of  chlorine  three  other  compounds  are 
successively  obtained,  each  poorer  in  hydrogen  and  richer  in  chlorine  than 
the  preceding,  the  ultimate  product  being  the  well-known  sesquichloride  of 
carbon  of  Mr.  Faraday. 

Hydrochloric  ether C4H5CI 

Monochlorinetted  hydrochloric  ether C4H4OI2 

Bichlorinetted C4H3OI3 

Trichlorinetted C4H2CI4 

Quadrichlorinetted C4H  Olg 

Sesquichloride  of  carbon C4    Olg 


DEBIVATIVES   OF   ALCOHOL   CONTAINING    SULPHUR. 

Mercaptan. — A  solution  of  caustic  potassa,  of  1-28  or  1-3  sp.  gr.,  is  satu 
rated  with  sulphuretted  hydrogen,  and  mixed  in  a  retort  with  an  equal  volume 
of  Bolution  of  sulphovinate  of  lime  of  the  same  density.     The  retort  li  con- 


ALCOHOL. 

ti'6<5tt5a  T^fth  a  ^ood"iiaili3etJSfer,  and  heat  is  applied  by  means  of  a  Tbath  of"  Bait 
and  water,  Mercaptan  and  water  distil  over  together,  and  are  easily  sepa- 
rated by  a  funnel.  The  product  thus  obtained  is  a  colourless,  limpid  liquid, 
of  sp.  gr.  0-842,  but  slightly  soluble  in  water,  easily  miscible,  on  the  con- 
trary, with  alcohol.  It  boils  at  97°  (36°C).  The  vapour  of  mercaptan  has 
a  most  intolerable  odour  of  onions,  which  adheres  to  the  clothes  and  person 
with  great  obstinacy ;  it  is  very  inflammable,  and  burns  with  a  blue  flame. 
Mercaptan  contains  C4HgS2=C4H5S,HS ;  or  alcohol,  having  sulphur  in  the 
place  of  oxygen. 

When  brought  into  contact  with  red  oxide  of  mercury,  even  in  the  cold, 
violent  reaction  ensues,'  water  is  formed,  and  a  white  substance  is  produced, 
soluble  in  alcohol,  and  separating  from  that  liquid  in  distinct  crystals,  which 
contain  C^HgSjHgS.  This  compound  is  decomposed  by  sulphuretted  hydro- 
gen, sulphide  of  mercury  being  thrown  down,  and  mercaptan  reproduced. 
By  adding  solutions  of  the  oxides  of  lead,  copper,  silver,  and  gold,  to  an 
alcoholic  solution  of  mercaptan,  corresponding  compounds  containing  those 
metals  are  formed.  Caustic  potassa  produces  no  effect  upon  mercaptan,  but 
potassium  displaces  hydrogen,  and  gives  rise  to  a  orystallizable  compound 
soluble  in  water. 

Xanthic  acid. — The  elements  of  ether  and  those  of  bisulphide  of  carbon 
combine  in  presence  of  an  alkali  to  a  very  extraordinary  substance,  possess- 
ing the  properties  of  an  oxygen-acid,  to  which  the  name  xanthic  is  applied, 
on  account  of  the  yellow  colour  of  one  of  its  most  permanent  and  charac- 
teristic salts,  that  of  oxide  of  copper.  Hydrate  of  potassa  is  dissolved  in 
12  parts  of  alcohol  of  0-800  sp.  gr. ;  into  this  solution  bisulphide  of  carbon 
is  dropped  until  it  ceases  to  be  dissolved,  or  until  the  liquid  loses  its  alka- 
linity. The  whole  is  then  cooled  to  0°  ( — 17° -80,  when  the  potassa-salt 
separates  in  the  form  of  brilliant,  slender,  colourless  prisms,  which  must  be 
quickly  pressed  between  folds  of  bibulous  paper,  and  dried  in  vacuo.  It  is 
freely  soluble  in  water  and  alcohol,  but  insoluble  in  ether,  and  is  gradually 
destroyed  by  exposure  to  air  by  oxidation  of  a  part  of  the  sulphur.  Hy- 
drated  xanthic  acid  may  be  prepared  by  decomposing  the  foregoing  com- 
pound by  dilute  sulphuric  or  hydrochloric  acid.  It  is  a  colourless,  oily 
liquid,  heavier  than  water,  of  powerful  and  peculiar  odour,  and  very  com- 
bustible ;  it  reddens  litmus-paper,  and  ultimately  bleaches  it.  Exposed  to 
gentle  heat,  it  is  decomposed  into  alcohol  and  bisulphide  of  carbon ;  this 
happens  at  a  temperature  of  75°  (23° -80).  Exposed  to  the  air,  or  kept  be- 
neath the  surface  of  water  open  to  the  atmosphere,  it  becomes  covered  with 
a  whitish  crust,  and  is  gradually  destroyed.  The  xanthates  of  the  alkalis 
and  of  baryta  are  colourless  and  crystallizable ;  the  lime-salt  dries  up  to  a 
gummy  mass ;  the  xanthates  of  the  oxides  of  zinc,  lead,  and  mercury  are 
white,  and  but  feebly  soluble,  that  of  copper  is  a  flocculent,  insoluble  sub- 
stance, of  beautiful  yellow  colour. 

Hydrated  xanthic  acid  contains  €5115840,  HO  ;  or  C4H50,C284,H0.  In  the 
Baits  this  water  is  replaced  by  one  equivalent  of  a  metallic  oxide. 


DERIVATIVES    OF   ALCOHOL    CONTAINING   METALS. 

Zinc-ethyl.  —  In  heating  iodide  of  ethyl  with  zinc  in  sealed  glass-tubes 
(see  compound  ethers;  ethyl-theory,  p.  352)  a  white  substance  remains  in 
the  tube,  which  is  a  mixture  of  iodide  of  zinc  and  a  peculiar  volatile  com- 

*  Whence  the  name,  mercurium  captans. 


ALCOHOL.    .  369 

pound,  to  which  t)r.  Frankland  has  given  the  name  zinc-ethyl.  It  may  be 
separated  from  the  residue  by  distilling  it  in  a  current  of  hydrogen,  when  it 
it  is  obtained  in  the  form  of  a  liquid  of  a  disagreeable  odour,  which  contains 
C^HgZn.  In  contact  with  atmospheric  air  it  is  rapidly  oxidized.  When 
mixed  with  water,  this  compound  is  decomposed  with  evolution  of  a  carbo- 
netted  hydrogen,  having  the  formula  C4Hg=C4H5,H,  which  may  be  viewed 
as  the  hydride  of  ethyl. 

Stibethyl. — Iodide  of  ethyl  when  distilled  with  an  alloy  of  antimony  and 
potassium,  yields  a  curious  substance,  which  MM.  Loewig  and  Schweizer 
have  described  under  the  name  of  stibethyl.  It  contains  SbCjjHjgzsSb  3 
(C4H5).  We  shall  return  to  this  substance  when  speaking  of  the  compound 
ammonias.* 


PRODUCTS  OF  THE  OXIDATION  OF  ALCOHOL. 

When  alcohol  and  ether  burn  with  flame  in  free  air,  the  products  of  their 
combustion  are,  as  with  all  bodies  of  like  chemical  nature,  carbonic  acid  and 
water.  Under  peculiar  circumstances,  however,  these  substances  undergo 
partial  oxidation,  in  which  the  hydrogen  alone  is  affected,  the  carbon  re- 
maining untouched.  The  result  is  the  production  of  certain  compounds, 
which  form  a  small  series,  supposed  by  some  chemists  to  contain  a  common 
radical,  to  which  the  name  acetyl  is  applied.  It  is  derived  from  ethyl  by  the 
oxidation  and  removal  of  2  eq.  of  hydrogen. 

Table  of  Acetyl- Compounds. 

Acetyl  (symbol  Ac)  C4H3 

Oxide  of  acetyl  (unknown)  C4H3O 

Hydrate  of  oxide  of  acetyl;  aldehyde  C4H30,HO 

Acetylous  acid ;  aldehydic  acid  C4H302,HO 

Acetylic  acid ;  acetic  acid  €411303,110 

Acetyl  and  its  protoxide  are  alike  hypothetical. 

Aldehyde,  C4H4OJ  or  AcO,HO. — This  substance  is  formed,  as  already  no- 
ticed, among  other  products,  when  the  vapour  of  ether  or  alcohol  is  trans- 
mitted through  a  red-hot  tube;  also,  by  the  action  of  chlorine  on  weak 
alcohol.  It  is  best  prepared  by  the  following  process :  —  6  parts  of  oil  of 
vitriol  are  mixed  with  4  parts  of  rectified  spirit  of  wine,  and  4  parts  of 
water ;  this  mixture  is  poured  upon  6  parts  of  powdered  binoxide  of  man- 
ganese, contained  in  a  capacious  retort,  in  connection  with  a  condenser, 
cooled  by  ice-cold  water.  Gentle  heat  is  applied ;  and  when  6  parts  of  liquid 
have  passed  over,  the  process  is  interrupted.  The  distilled  product  is  put 
into  a  small  retort,  with  its  own  weight  of  chloride  of  calcium,  and  redis- 
tilled ;  the  operation  is  repeated.  The  aldehyde,  still  retaining  alcohol,  and 
other  impurities,  is  mixed  with  twice  its  volume  of  ether,  and  saturated 
with  dry  ammoniacal  gas ;  a  crystalline  compound  of  aldehyde  and  ammonia 
separates,  which  may  be  washed  with  a  little  ether,  and  dried  in  the  air. 
From  this  substance  the  aldehyde  may  be  separated  by  distillation  in  a 
water-bath,  with  sulphuric  acid,  diluted  with  an  equal  quantity  of  water ; 
by  careful  rectification  from  chloride  of  calcium,  at  a  temperature  not  ex- 
ceeding 87°  (30°-5C),  it  is  obtained  pure  and  anhydrous. 

»  Bismaethyl,  BiCuHi6=Bi  3(C4H5).  Stanethyl,  SnC4Hs  and  tellurethyl,  TeC4H5  have  alsc 
been  produced  by  similar  reactions  and  some  of  their  compounds  investigated.  —  R.  B. 


SYO  ALDEHYDIC    ACID. 

Aldehyde '  is  a  limpid,  colourless  liquid,  of  characteristic  ethereal  odour, 
•which,  when  strong,  is  exceedingly  suffocating.  It  has  a  density  of  0-790, 
boils  at  72°  (22° -30),  and  mixes,  in  all  proportions,  with  water,  alcohol,  and 
ether;  it  is  neutral  to  test-paper,  but  acquires  acidity  on  exposure  to  air, 
from  the  production  of  acetic  acid ;  under  the  influence  of  platinum-black 
this  change  is  very  speedy.  When  a  solution  of  this  compound  is  heated 
with  caustic  potassa,  a  remarkable  brown,  resin-like  substance  is  produced, 
the  so-called  aldehyde-resin.  Gently  heated  with  protoxide  of  silver,  it  reduces 
the  latter  without  evolution  of  gas,  the  metal  being  deposited  on  the  inner 
surface  of  the  vessel  as  a  brilliant  and  uniform  film ;  the  liquid  contains  alde- 
hydate  of  silver. 

When  treated  with  hydrocynic  acid,  aldehyde  yields  a  substance  called 
alanine,  which  was  already  noticed,  when  treating  of  lactic  acid,  and  which 
will  be  described  more  in  detail  in  the  section  on  vegeto-alkalis,  under  the 
head  of  bases  from  aldehyde. 

The  action  of  sulphuretted  hydrogen  upon  the  ammonia-compound  .gives 
rise  to  the  formation  of  thialdine,  noticed  likewise  under  the  head  of  bases 
from  aldehyde. 

The  ammonia-compound  above  mentioned  forms  transparent,  colourless 
crystals  of  great  beauty ;  it  has  a  mixed  odour  of  ammonia  and  turpentine ; 
it  dissolves  very  easily  in  water,  with  less  facility  in  alcohol,  and  with  diffi- 
culty in  ether;  it  melts  at  about  170°  (76°C),  and  distils  unchanged  at  212° 
(100°C).  Acids  decompose  it,  with  production  of  ammoniacal  salt  and  sepa- 
ration of  aldehyde.  The  crystals,  which  are  apt  to  become  yellow,  and  lose 
their  lustre  in  the  air,  contain  C4H4O2+NH3. 

When  pure  aldehyde  is  long  preserved  in  a  close-stopped  vessel,  it  is 
sometimes  found  to  undergo  spontaneous  change  into  one,  and  even  two  iso- 
meric modifications,  differing  completely  in  properties  from  the  original 
compound.  In  a  specimen  kept  some  weeks  at  32°  (0°C),  transparent  acicular 
crystals  were  observed  to  form  in  considerable  quantity,  which,  at  a  tempe- 
rature little  exceeding  that  of  the  freezing-point  of  water,  melted  to  a  colour- 
less liquid,  miscible  with  water,  alcohol,  and  ether ;  a  few  crystals  remained, 
which  sublimed  without  fusion,  and  were  probably  composed  of  the  second 
substance.  This  new  body  received  the  name  elaldehtjdc ;  it  was  found  to  be 
identical  in  composition  with  aldehyde,  but  to  differ  in  properties  and  in  the 
density  of  its  vapour;  the  latter  has  a  sp.  gr.  of  4-515,  while  that  of  alde- 
hyde is  only  1-532,  or  one-third  of  that  number.  It  refuses  to  combine  with 
ammonia,  is  not  rendered  brown  by  potassa,  and  is  but  little  affected  by 
solution  of  silver. 

The  second  modification,  or  metaldehyde,  is  sometimes  produced  in  pure 
aldehyde,  kept  at  the  common  temperature  of  the  air,  even  in  hermetically- 
sealed  tubes;  the  conditions  of  its  formation  are  unknown.  It  "forms  colour- 
less, transparent,  prismatic  crystals,  which  sublime  without  fusion  at  a 
temperature  above  212°  (100°),  and  are  soluble  in  alcohol  and  ether,  but  not 
in  water.  They  also  were  found,  by  analysis,  to  have  the  same  composition 
as  aldehyde.  The  substance  which  we  have  described  by  the  term  of  chloral 
may  be  viewed  as  bichlorinetted  aldehyde. 

Aldehydic  acid,  CJIsOg.HO.  —  When  solution  of  aldehydate  of  silver, 
obtained  by  digesting  oxide  of  silver  in  excess  with  aldehyde,  is  precipitated 
Dy  sulphuretted  hydrogen,  an  acid  liquid  is  obtained,  which  neutralizes 
alkalis,  and  combines  with  the  oxides  of  the  metals.  It  is  very  easily  decom- 
posed. Aldehylate  of  silver,  mixed  with  baryta-water,  gives  rise  to  aldehy- 
date of  baryta  and  oxide  of  silver :  if  this  precipitate  be  heated  in  the  liquid, 

« Alcohol  dehydrogenatus. 


ACETIC    ACID.  371 

the  metal  is  reduced,  and  neutral  acetate  of  baryta  formed ;  whence  it  is  in- 
ferred that  the  new  acid  contains  the^elements  of  the  acetic  acid,  minus  an 
equivalent  of  oxygen. 

AcETAL. — This  substance  is  one  of  the  products  of  the  slow  oxidation  of 
alcohol-vapour  under  the  influence  of  platinum-black.  Spirit  of  wine  is 
poured  into  a  large,  tall,  glass-jar,  to  the  depth  of  about  an  inch,  and  a 
shallow  capsule,  containing  slightly -moistened  platinum -black,  arranged 
above  the  surface  of  the  liquid  ;  the  jar  is  loosely  covered  by  a  glass  plate, 
and  left  during  two  or  three  weeks,  in  a  warm  situation.  At  the  expiration 
of  that  period  the  liquid  is  found  highly  acid ;  it  is  to  be  neutralized  with 
carbonate  of  potassa,  as  much  chloride  of  calcium  added  as  the  liquid  will 
dissolve,  and  the  whole  subjected  to  distillation,  the  first  fourth  only  being 
collected.  Fused  chloride  of  calcium  added  to  the  distilled  product  now 
throws  up  a  light  oily  liquid,  which  is  a  mixture  of  acetal  with  alcohol, 
aldehyde,  and  acetic  ether.  By  fresh  treatment  with  chloride  of  calcium, 
and  long  exposure  to  gentle  heat  in  a  retort,  the  aldehyde  is  expelled.  The-. 
acetic  ether  is  destroyed  by  caustic  potassa,  and  the  alcohol  removed  by 
washing  with  water,  after  which  the  acetal  is  again  digested  with  fused 
chloride  of  calcium,  and  re-distilled. 

Pure  acetal  is  a  thin,  colourless  fluid,  of  agreeable  ethereal  odour  of  sp. 
gr.  0  821  at  72°  (22o-2C),  and  boiling  at  220°  (104°C).  It  is  soluble  in  18 
parts  of  water,  and  miscible  in  all  proportions  with  alcohol  and  ether.  It  is 
unchanged  in  the  air ;  but,  under  the  influence  of  platinum-black,  becomes 
converted  into  aldehyde,  and  eventually  into  acetic  acid.  Nitric  and  chromic 
acids  produce  a  similar  eff"ect.  Strong  boiling  solution  of  potassa  has  no 
action  on  this  substance.  Acetal  contains  CJ2HJ4O4,  or  the  elements  of  2  eq. 
ether  and  1  eq.  aldehyde,  C^2^ljfi^=2C^\i^O+C^E^02. 

When  a  coil  of  fine  platinum  wire  is  heated  to  redness,  and  plunged  into 
a  mixture  of  ether,  or  alcohol-vapour  and  atmospheric   air,  it  determines 
upon  its  surface  the  partial  combustion  of  the  former,  and  gives  rise  to  an 
excessively  pungent  acrid  vapour,  which  may  be  con- 
densed to  a  colourless  liquid  by  suitable  means.     The  Fig.  169. 
heat  evolved  in  the  act  of  oxidation  is  sufficient  to  main- 
tain the  wire  in  an  incandescent  state.     The  experiment 
may  be  made  by  putting  a  little  ether  into  an  ale-glass, 
fig.  169,  and  suspending  over  it  the  heated  spiral  from 
a  card ;  or  by  slipping  the  coil  over  the  wick  of  a  spirit- 
lamp,  so  that  the  greater  part  may  be  raised  above  the 
cotton;    the  lamp  is  supplied  with  ether  or  spirit  of 
wine,  lighted  for  a  moment,  and  then  blown  out.     The 
coil  continues  to  glow  in  the  mixed  atmosphere  of  air 
and  combustible  vapour,  until  the  ether  is   exhausted. 
This  is  the  lamp  without  flame  of  Sir  H.  Davy.     A  ball 
of  spongy  platinum  may  be  substituted  for  the  coil  of 
wire.     The  condensed  liquid  contains  acetic  and  formic 
acids  with  aldehyde  and  aldehydic  acid. 

Acetic  Acid. — Pure  alcohol,  exposed  to  the  air,  or  thrown  into  a  vessel 
of  oxygen  gas,  fails  to  suffer  the  slightest  change  by  oxidation  ;  when 
diluted  with  water,  it  remains  also  unaffected.  If,  on  the  other  hand,  s^it 
S^  v9ipe  be  dropped  upon  dry  platinum-black,  the  oxygen  condensed  into  the 
pores  of  the  latter,  reacts  so  powerfully  upon  the  alcohol  as  to  cause  its 
instant  inflammation.  When  the  spirit  is  mixed  with  a  little  water,  and 
slowly  dropped  upon  the  finely  divided  metal,  oxidation  still  takes  place,  but 
with  less  energy,  and  vapour  of  acetic  acid  is  abundantly  evolved.  It  is 
almost  unnecessary  to  add,  that  the  platinum  itself  undergoes  no  change  in 
this  experiment. 


J, 


372  ACETIC    ACID. 

Dilute  alcohol,  mixed  with  a  little  yeast,  or  almost  any  azotized  organic 
matter,  susceptible  of  putrefaction,  and  exposed  to  the  air,  speedily  becomes 
oxidized  to  acetic  acid.  Acetic  acid  is  thus  manufactured  in  Germany,  by 
Buffering  such  a  mixture  to  flow  over  wood-shavings,  steeped  in  a  little  vine- 
gar, contained  in  a  large  cylindrical  vessel,  through  which  a  current  of  air 
is  made  to  pass.  The  greatly  extended  surface  of  the  liquid  expedites  the 
change,  which  is  completed  in  a  few  hours.  No  carbonic  acid  is  produced 
in  this  reaction. 

The  best  vinegar  is  made  from  wine  by  spontaneous  acidification  in  a 
partially  filled  cask  to  which  the  air  has  access.  Vinegar  is  first  introduced 
into  the  empty  vessel,  and  a  quantity  of  wine  added ;  after  some  days  a 
second  portion  of  wine  is  poured  in,  and  after  similar  intervals  a  third  and 
a  fourth.  When  the  whole  has  become  vinegar,  a  quantity  is  drawn  off 
equal  to  that  of  the  wine  employed,  and  the  process  is  recommenced.  The 
temperature  of  the  building  is  kept  up  to  86°  (30°C).  Such  is  the  plan 
adopted  at  Orleans.'  In  England  vinegar  of  an  inferior  description  is  pre- 
pared from  a  kind  of  beer  made  for  the  purpose.  The  liquor  is  exposed  to 
the  air  in  half-empty  casks,  loosely  stopped,  until  acidification  is  complete. 
A  little  sulphuric  acid  is  afterwards  added,  with  a  view  of  checking  farther 
decomposition,  or  mothering,  by  which  the  product  would  be  spoiled. 

There  is  another  source  of  acetic  acid  besides  the  oxidation  of  alcohol : 
when  dry,  hard  wood,  as  oak  and  beech,  is  subjected  to  destructive  distilla- 
tion at  a  red-heat,  acetic  acid  is  found  among  the  liquid  condensable  pro- 
ducts of  the  operation.  The  distillation  is  conducted  in  an  iron  cylinder  of 
large  dimensions,  to  which  a  worm  or  condenser  is  attached  ;  a  sour  watery 
liquid,  a  quantity  of  tar,  and  much  inflammable  gas  pass  over,  while  char- 
coal of  excellent  quality  remains  in  the  retort.  The  acid  liquid  is  subjected 
to  distillation,  the  first  portion  being  collected  apart  for  the  sake  of  a  pecu- 
liar volatile  body,  shortly  to  be  described,  which  it  contains.  The  remainder 
is  saturated  with  lime,  concentrated  by  evaporation,  and  mixed  with  solu- 
tion of  sulphate  of  soda;  sulphate  of  lime  precipitates,  while  the  acetic 
acid  is  transferred  to  the  soda.  The  filtered  solution  is  evaporated  to  its 
crystallizing-point ;  the  crystals  are  drained  as  much  as  possible  from  the 
dark,  tarry  mother-liquid,  and  deprived  by  heat  of  their  combined  water. 
The  dry  salt  is  then  cautiously  fused,  by  which  the  last  portions  of  tar  are 
decomposed  or  expelled ;  it  is  then  re-dissolved  in  water,  and  re-crystallized. 
Pure  acetate  of  soda,  thus  obtained,  readily  yields  hydrated  acetic  acid  by 
distillation  with  sulphuric  acid.  ^ 

The  strongest  acetic  acid  is  prepared  by  distilling  finely  powdered  anhy- 
drous acetate  of  soda  with  three  times  its  weight  of  concentrated  oil  of 
vitriol.  The  liquid  is  purified  by  rectification  from  sulphate  of  soda,  acci- 
dentally thrown  up,  and  then  exposed  to  a  low  temperature.  Crystals  of 
hydrate  of  acetic  acid  form  in  large  quantity,  which  may  be  drained  from 
the  weaker  fluid  portion,  and  then  suffered  to  melt.  Below  60°  (15°-5C) 
this  substance  forms  large,  colourless,  transparent  crystals,  which  above 
that  temperature  fuse  to  a  thin,  colourless  liquid,  of  exceedingly  pungent 
and  well-known  odour ;  it  raises  blisters  on  the  skin.  It  is  miscible  in  all 
proportions  with  water,  alcohol,  and  ether,  and  dissolves  camphor  and 
several  resins.  When  diluted  it  has  a  pleasant  acid  taste.  The  hydrate  of 
acetic  acid  in  the  liquid  condition  has  a  density  of  1-063,  and  boils  at  246° 
(119°C) :  its  vapour  is  inflammable.  Acetic  acid  forms  a  great  number  of 
exceedingly  important  salts,  all  of  which  are  soluble  in  water ;  the  acetates 
of  silver  and  mercury  are  the  least  soluble. 

The  hydrate  of  acetic  acid  contains  C4H303,H0  =  Ac03,H0;  it  is  formed 

*  Dumas,  Chimie  appliqu^e  aux  Arts,  vi.  537. 


ACETIC    ACID.  S73 

from  alcohol  by  the  substitution  of  2  eq.  of  oxygen  for  2  eq.  of  hy  irogen. 
The  water  is  basic,  and  can  be  replaced  by  metallic  oxides.  A  different  vie-w 
regarding  the  constitution  of  this  acid  has  been  proposed  by  Prof.  Kolbe ;  it 
is  chiefly  based  upon  the  remarkable  decomposition  which  acetic  acid  under- 
goes when  submitted  to  the  action  of  the  galvanic  current.  We  shall  return 
to  this  subject  when  speaking  of  valerianic  acid. 

Dilute  acetic  acid,  or  distilled  vinegar,  used  in  pharmacy,  should  always 
be  carefully  examined  for  copper  and  lead ;  these  impurities  are  contracted 
from  the  metallic  vessel  or  condenser  sometimes  employed  in  the  process. 
The  strength  of  any  sample  of  acetic  acid  cannot  be  safely  inferred  from'  its 
density,  but  is  easily  determined  by  observing  the  quantity  of  dry  carbonate 
of  soda  necessary  to  saturate  a  known  weight  of  the  liquid.* 

Acetate  of  potassa,  K0,C4H303. — This  salt  crystallizes  with,  great  diflS- 
culty  ;  it  is  generally  met  with  as  a  foliated,  white,  crystalline  mass,  obtained 
by  neutralizing  carbonate  of  potassa  by  acetic  acid,  evaporating  to  dryness, 
and  heating  the  salt  to  fusion.  The  acetate  is  extremely  deliquescent,  and 
soluble  in  water  and  alcohol ;  the  solution  is  usually  alkaline,  from  a  little 
loss  of  acid  by  the  heat  to  which  it  has  been  subjected.  From  the  alcoholic 
solution,  carbonate  of  potassa  is  thrown  down  by  a  stream  of  carbonic  acid. 
Acetate  of  soda,  NaO,C4H303-}-6HO. — The  mode  of  preparation  of  this 
salt  on  the  large  scale  has  been  already  described ;  it  forms  large,  transpa- 
rent, colourless  crystals,  derived  from  a  rhombic  prism,  which  are  easily 
rendered  anhydrous  by  heat,  effloresce  in  dry  air,  and  dissolve  in  3  parts  of 
cold,  and  in  an  equal  weight  of  hot  water, — it  is  also  soluble  in  alcohol.  The 
taste  of  this  substance  is  cooling  and  saline.  The  dry  salt  undergoes  the 
igneous  fusion  at  550°  (287°-8C),  and  begins  to  decompose  at  600°  (315°-5C). 
Acetate  of  ammonia;  spirit  of  Minderekus  ;  NH40,C4H308. — The  neu- 
tral solution  obtained  by  saturating  strong  acetic  acid  by  carbonate  of  am- 
monia cannot  be  evaporated  without  becoming  acid  from  loss  of  base ;  the 
salt  passes  oif  in  large  quantity  with  the  vapour  of  water.  Solid  acetate  of 
ammonia  is  best  prepared  by  distilling  a  mixture  of  equal  parts  of  acetate  of 
lime  and  powdered  salammoniac ;  chloride  of  calcium  remains  in  the  retort. 
A  saturated  solution  of  the  solid  salt  in  hot  water,  suflFered  slowly  to  cool  in 
a  close  vessel,  deposits  long  slender  crystals,  which  deliquesce  in  the  air 
Acetate  of  ammonia  has  a  sharp  and  cooling,  yet  sweet,  taste ;  its  solution 
becomes  alkaline  on  keeping,  from  decomposition  of  the  acid. 

Acetate  of  ammonia  when  distilled  with  anhydrous  phosphoric  acid,  loses 
4  eq.  of  water,  being  converted  into  a  colourless  liquid  inmiscible  with  water, 
of  an  aromatic  odour,  and  boiling  at  170°  (77°C)  which  has  received  the 
name  of  acetonitrile  C4H3N.  When  boiled  with  acids  or  alkalis  it  re-assimi- 
lates the  4  eq.  of  water,  being  converted  again  into  acetic  acid  and  ammonia. 
This  substance  is  the  type  of  a  class  ;  great  many  ammonia-salts  of  acids, 
analagous  to  acetic  acid,  undergoing  a  similar  change  when  treated  with  an- 
hydrous phosphoric  acid.  It  is  likewise  obtained  by  a  perfectly  different 
process,  which  will  be  described  when  treating  of  the  methyl-compounds. 
(See  cyanide  of  methyl,  page  383,  and  also  acetic  ether,  page  356.) 

The  acetates  of  lime,  baryta,  and  strontia  are  very  soluble,  and  can  be  pro- 
cured in  crystals ;  acetate  of  magnesia  crystallizes  with  difficulty. 

Acetate  of  alumina,  Al203,3C4H303. — This  salt  is  very  soluble  in  water, 
and  dries  up  in  the  vacuum  of  the  air-pump  to  a  gummy  mass,  without  trace 

*  Acetic  acid  increases  in  density  by  the  addition  of  water,  and  reaches  its  maximum  1.07S 
when  30  parts  have  been  mixed  with  100  of  the  strongest  acid;  it  then  decreases  in  densit>. 
and  when  135  parts  have  been  added  its  specific  gravity  is  the  same  as  the  hydrate,  1.063° 
The  most  ready  method  to  test  its  strength  is  to  suspend  in  it  a  fragment  of  pure  marble  of 
known  weight;  the  loss  of  weight  resulting  will  be  five  sixths  of  the  weight  of  the  hydrated 
acid  present,  50  parts  of  carbonate  of  lime  being  required  to  saturate  60  parta  of  aceti* 
acid.— R.  B. 
82 


374  ACETIC    ACID. 

of  crystallization.  If  foreign  salts  be  present,  the  solution  of  the  acetate 
becomes  turbid  on  heating,  from  the  separation  of  a  basic  compound,  which 
re-dissolves  as  the  liquid  cools.  Acetate  of  alumina  is  much  employed  in 
calico-printing ;  it  is  prepared  by  mixing  solutions  of  acetate  of  lead  and 
alum,  and  filtering  from  the  insoluble  sulphate  of  lead.  The  liquid  is  thick- 
ened with  gum  or  other  suitable  material,  and  with  it  the  design  is  impressed 
upon  the  cloth  by  a  wood-block,  or  by  other  means.  Exposure  to  a  moderate 
degree  of  heat  drives  off  the  acetic  acid,  and  leaves  the  alumina  in  a  state 
capable  of  entering  into  combination  with  the  dye-stuff. 

Acetate  of  manganese  forms  colourless,  rhombic,  prismatic  crystals,  perma- 
nent in  the  air.  Acetate  of  protoxide  of  iron  crystallizes  in  small  greenish- 
white  needles,  very  prone  to  oxidation ;  both  salts  dissolve  freely  in  water. 
Acetate  of  sesquioxide  of  iron  is  a  dark-brownish  red,  uncrystallizable  liquid, 
of  powerful  astringent  taste.  Acetate  of  cobalt  forms  a  violet-coloured,  crys- 
talline, deliquescent  mass.  The  nickel-salt  separates  in  green  crystals,  which 
dissolve  in  6  parts  of  water.  • 

Acetate  of  lead,  PbO,  C^HgOg-fSHO. — This  important  salt  is  prepared 
on  a  large  scale  by  dissolving  litharge  in  acetic  acid ;  it  may  be  obtained  in 
colourless,  transparent,  prismatic  crystals,  but  is  generally  met  with  in  com- 
merce as  a  confusedly  crystalline  mass,  somewhat  resembling  loaf-sugar. 
From  this  circumstance,  and  from  its  sweet  taste,  it  is  often  called  sugar  of 
lead.  The  crystals  are  soluble  in  about  1\  parts  of  cold  water,  effloresce  in 
dry  air,  and  melt  when  gently  heated  in  their  water  of  crystallization ;  the 
latter  is  easily  driven  off,  and  the  anhydrous  salt  obtained,  which  suffers  the 
igneous  fusion,  and  afterwards  decomposes,  at  a  high  temperature.  Acetate 
of  lead  is  soluble  in  alcohol.  The  watery  solution  has  an  intensely  sweet, 
and  at  the  same  time  astringent,  taste,  and  is  not  precipitated  by  ammonia. 
It  is  an  article  of  great  value  to  the  chemist. 

Basic  acetates  (subacetatbs)  of  lead.  —  Sesgui-lasic  acetate  is  produced 
when  the  neutral  anhydrous  salt  is  so  far  decomposed  by  heat  as  to  become 
converted  into  a  porous  white  mass,  decomposable  only  at  a  much  higher 
temperature.  It  is  soluble  in  water,  and  separates  from  the  solution  evapo- 
rated to  a  syrupy  consistence  in  the  form  of  crystalline  scales.  It  contains 
3PbO,2C4H303.  A  sub-acetate  with  3  eq.  of  base  is  obtained  by  digesting  at 
a  moderate  heat  7  parts  of  finely-powdered  litharge,  6  parts  of  acetate  of 
lead,  and  30  parts  of  water.  Or,  by  mixing  a  cold  saturated  solution  of  neu- 
tral acetate  with  a  fifth  of  its  volume  of  caustic  ammonia,  and  leaving  the 
whole  some  time  in  a  covered  vessel ;  the  salt  separates  in  minute  needles, 
which  contain  3PbO,C4H303-}-HO.  The  solution  of  sub-acetate  prepared  by 
the  first  method  is  known  in  pharmacy  under  the  name  of  Goulard  tvater. 
A  third  sub-acetate  exists,  formed  by  adding  a  great  excess  of  ammonia  to  a 
solution  of  acetate  of  lead,  or  by  digesting  acetate  of  lead  with  a  large  quan- 
tity of  oxide.  It  is  a  white,  slightly  crystalline  substance,  insoluble  in  cold, 
and  but  little  soluble  in  boiling  water.  It  contains  GPbO.QHgOg.  The  solu- 
tions of  the  sub-acetates  of  lead  have  a  strong  alkaline  reaction,  and  absorb 
carbonic  acid  with  the  greatest  avidity,  becoming  turbid  from  the  precipita 
tion  of  basic  carbonate. 

Acetate  of  copper.  —  The  neutral  acetate,  CuO,C4H303-j-HO,  is  prepared 
by  dissolving  verdigris  in  hot  acetic  acid,  and  leaving  the  filtered  solution  to 
cool.  It  forms  beautiful  dark-green  crystals,  which  dissolve  in  14  parts  of 
cold  and  5  parts  of  boiling  water,  and  are  also  soluble  in  alcohol.  A  solution 
ot  this  salt,  mixed  with  sugar  and  heated,  jdelds  suboxide  of  copper  in  the 
form  of  minute  red  octahedral  crystals;  the  residual  copper  solution  is  not 
precipitated  by  an  alkali.  Acetate  of  copper  furnishes,  by  destructive  disti] 
lation,  strong  acetic  acid,  containing  acetone,  and  contaminated  with  copper. 
The  salt  i»  sometimes  called  distilled  verdigris,  and  is  used  as  a  pigment 


CHLORACETTC   ACID.  375 

Basic  acetates  (sub-acetates)  of  copper.  —  Common  verdigris,  made 
by  spreading  the  marc  of  grapes  upon  plates  of  copper  exposed  to  the  air 
during  several  -^veeks,  or  by  substituting,  with  the  same  view,  pieces  of  cloth 
dipped  in  crude  acetic  acid,  is  a  mixture  of  several  basic  acetates  of  copper 
which  have  a  green  or  blue  colour.  One  of  these,  3CuO,2C4H303-(-6HO,  is 
obtained  by  digesting  the  powdered  verdigris  in  warm  water,  and  leaving  the 
soluble  part  to  spontaneous  evaporation.  It  forms  a  blue,  crystalline  mass, 
but  little  soluble  in  cold  water.  When  boiled,  it  deposits  a  brown  powder, 
which  is  a  sub-salt  with  large  excess  of  base.  The  green  insoluble  residue 
of  the  verdigris  contains  SCuOjC^HgOg-f-SHO  :  it  may  be  formed  by  digesting 
neutral  acetate  of  copper  with  the  hydrated  oxide.  I5y  ebullition  with  water 
U  is  resolved  into  neutral  acetate  and  the  brown  sub-salt. 

Acetate  of  silver,  AgO,C4H303,  is  obtained  by  mixing  acetate  of  potassa 
with  nitrate  of  silver,  and  washing  the  precipitate  with  cold  water  to  remove 
the  nitrate  of  potassa.  It  crystallizes  from  a  warm  solution  in  small  colour- 
less needles,  which  have  but  little  solubility  in  the  cold. 

Acetate  of  suboxide  of  mercury  forms  small  scaly  crystals,  which  are  as  feebly 
soluble  as  those  of  acetate  of  silver.  The  salt  of  the  red  oxide  of  mercury  dis- 
solves with  facility. 

Chloracetic  acid.  —  "When  a  small  quantity  of  crystallizable  acetic  acid 
is  introduced  into  a  bottle  of  dry  chlorine  gas,  and  the  whole  exposed  to  the 
direct  solar  rays  for  several  hours,  the  interior  of  the  vessel  is  found  coated 
with  a  white  crystalline  substance,  which  is  a  mixture  of  the  new  product, 
the  chloracetic  acid,  with  a  small  quantity  of  oxalic  acid.  The  liquid  at  the 
bottom  contains  the  same  substances,  together  with  the  unaltered  acetic  acid. 
Hydrochloric  and  carbonic  acid  gases  are  at  the  same  time  produced,  together 
with  suffocating  vapour,  resembling  chloro-carbonic  acid.  The  crystalline 
matter  is  dissolved  out  with  a  small  quantity  of  water,  added  to  the  liquid 
contained  in  the  bottle,  and  the  whole  placed  in  the  vacuum  of  the  air-pump, 
with  capsules  containing  fragments  of  caustic  potassa,  and  concentrated  sul- 
phuric acid.  The  oxalic  acid  is  first  deposited,  and  afterwards  the  new  sub- 
stance in  beautiful  rhombic  crystals.  If  the  liquid  refuses  to  crystallize,  it 
may  be  distilled  with  a  little  anhydrous  phosphoric  acid,  and  then  evaporated. 
The  crystals  are  spread  upon  bibulous  paper  to  drain,  and  dried  in  vacuo. 

Chloracetic  acid  is  a  colourless  and  extremely  deliquescent  substance ;  it 
has  a  faint  odour,  and  a  sharp,  caustic  taste,  bleaching  the  tongue  and 
destroying  the  skin;  the  solution  is  powerfully  acid.  At  115°  (46°C)  it 
melts  to  a  clear  liquid,  and  at  390°  (218°-8C)  boils  and  distils  unchanged. 
The  density  of  the  fused  acid  is  1  -617 ;  that  of  the  vapour,  which  is  very  irri- 
tating, is  probably  5  6.  The  substance  contains,  according  to  the  analysis 
of  M.  Dumas,  C4Cl303,H0,  or  the  elements  of  hydrated  acetic  acid  from 
which  3  eq.  of  hydrogen  have  been  withdrawn,  and  3  eq.  of  chlorine  substi- 
tuted. 

Chloracetic  acid  forms  a  variety  of  salts,  which  have  been  examined  and 
described ;  it  combines  also  with  ether,  and  with  the  ether  of  wood-spirit. 
These  compounds  correspond  to  the  ethers  of  the  other  organic  acid.  Chlora- 
cetate  of  potassa  crystallizes  in  fibrous,  silky  needles,  which  are  permanent 
in  the  air,  and  contain  KCC^ClgOg+HO.  The  ammoniacal  salt  is  also  crys- 
tallizable and  nexitral ;  it  contains  NH40,C4Cl303-(-5H0.  Chloracetate  ofsilvei 
is  a  soluble  compound,  crystallizing  in  small  greyish  scales,  which  are  easily 
altered  by  light;  it  gives,  on  analysis,  AgO,C4Cl303,  and  is  cotsequently 
anhydrous. 

When  chloracetic  acid  is  boiled  with  an  excess  of  ammonia,  it  is  decoin 
posed,  with  production  of  chloroform  and  carbonate  of  ammonia. 

C,TI  C\0^=C^\{  Clg  and  i\0^. 


576^  ACETONE. 

With  caustic  potassa,  it  yields  a  smaller  quantity  of  chloroform,  chloride 
of  potassium,  carbonate  and  formate  of  potassa.  The  chloride  and  the  for- 
mate are  secondary  products  of  the  reaction  of  the  alkali  upon  the  chloro- 
form. 

Normal  acetic  maybe  reproduced  from  this  curious  substitution-compound. 
When  an  amalgam  of  potassium  and  mercury  is  put  into  a  strong  aqueous 
solution  of  chloracetic  acid,  chemical  action  ensues,  the  temparature  of  the 
liquid  rises,  without  disengagement  of  gas,  and  the  solution  is  found  to  con- 
tain acetate  of  potassa,  chloride  of  potassium,  and  some  caustic  potassa. 

Acetone;  pyroacetic  spirit. — When  metallic  acetates  in  an  anhydrous 
state  are  subjected  to  destructive  distillation,  they  yield,  among  other  pro- 
ducts, a  peculiar  inflammable,  volatile  liquid,  designated  by  the  above  names. 
It  is  most  easily  prepared  by  distilling  carefully  dried  acetate  of  lead  in  a 
Lirge  earthen  or  coated  glass  retort,  by  a  heat  gradually  raised  to  redness; 
the  retort  must  be  connected  with  a  condenser  well  supplied  with  cold  water. 
Much  gas  is  evolved,  chiefly  carbonic  acid,  and  the  volatile  product,  but 
slightly  contaminated  with  tar,  collects  in  the  receiver.  The  retort  is  found 
after  the  operation  to  contain  minutely  divided  metallic  lead,  which  is  some- 
times pyrophoric.  The  crude  acetone  is  saturated  with  carbonate  of  po- 
tassa, and  afterwards  rectified  in  a  water-bath  from  chloride  of  calcium. 
This  compound  may  also  be  prepared  by  passing  the  vapour  of  strong  acetic 
acid  through  an  iron  tube  heated  to  dull  redness ;  the  acid  is  resolved  into 
acetone,  carbonic  acid,  carbonic  oxide,  and  carbonetted  hydrogen. 

Pure  acetone  is  a  colourless  limpid  liquid,  of  peculiar  odour;  it  has  a 
density  of  0-792,  and  boils  at  132°  (55°oC);  the  density  of  its  vapour, 
2-022.  Acetone  is  very  inflammable,  and  burns  with  a  bright  flame ;  it  is 
miscible  in  all  proportions  with  water,  alcohol,  and  ether.  The  simplest 
formula  of  this  substance  which  is  produced  by  the  resolution  of  acetic  acid 
into  acetone  and  carbonic  acid,  is  CgHgO ;  but  it  is  probable  that  this  for- 
mula should  be  doubled. 

When  acetone  is  distilled  with  half  its  volume  of  Nordhausen  sulphuric 
acid,  an  oily  liquid  is  obtained,  which  in  a  state  of  purity  has  a  feeble  garlic 
odour.  It  is  lighter  than  water,  and  very  inflammable.  It  contains  CigHjj, 
and  is  produced  by  the  abstraction  of  the  elements  of  water  from  acetone. 
It  has  received  the  name  mesitilole.  If  pentachloride  of  phosphorus  be 
dropped  into  carefully  cooled  acetone,  and  the  whole  mixed  with  water,  a 
heavy  oily  liquid  separates,  which  is  stated  to  contain  CgHgCl.  When  this 
is  dissolved  in  alcohol,  and  mixed  with  caustic  potassa,  a  second  oily  pro- 
duct results.  This  is  lighter  than  water,  has  an  aromatic  odour,  and  con- 
tains CgHgO. 

Sir  llobert  Kane  has  described  a  number  of  other  compounds  formed  by 
the  action  of  acids,  and  other  chemical  agents,  on  acetone,  from  which  he 
has  inferred  the  existence  of  an  organic  salt-basyle,  containing  CgHg,  and  to 
which  the  name  of  mesityl  has  been  given.  Zeise,  on  the  other  hand,  has 
shown  that  by  the  action  of  chloride  of  platinum  upon  acetone,  a  yellow 
crystallizable  compound  can  be  obtained,  having  a  composition  expressed  by 
the  formula  CgllgO-f-PtCV 

Acetic  acid  is  not  the  only  source  of  acetone ;  it  is  produced  in  the  de- 
structive distillation  of  citric  acid,  and  may  be  procured  from  sugar,  starch, 
and  gum  by  distillation  with  8  times  their  weight  of  powdered  quick-lime 
The  acetone  is,  in  this  case,  accompanied  by  an  oily,  volatile  liquid,  sepa- 
rable by  water,  in  which  it  is  insoluble.  This  substance  is  called  metaceione 
ov  propione ;  it  contains  CgHgO,  its  boiling-point  is  212°  (100°C). 

Propionic  acid.  —  Metacetone  distilled  with  a  mixture  of  bichromate  of 
potassa  and  sulphuric  acid  yields,  among  other  products,  metacetonic  or  pro- 
pionic acid  CgHgOjjHO,  a  volatile  acid,  very  closely  resembling  acetic  acid, 


KAKODYL    AND    ITS    COMPOUNDS.  377 

and  chiefly  distinguished  from  that  substance  by  the  high  degree  of  solu- 
bility of  its  soda-salt,  Mr.  Morley  has  lately  shown  that  propionate  of  ba- 
ryta when  submitted  to  destructive  distillation,  yields  again  propione.  Pro- 
pionic acid  is  one  of  the  products  of  the  action  of  hydrate  of  potassa  in  a 
melted  state  upon  sugar,  and  is  also  generated  by  the  fermentation  of  gly- 
cerin. The  formation  of  this  substance  by  the  action  of  potassa  upon  cy- 
anide of  ethyl  has  been  already  mentioned,  page  354. 

When  acetate  of  potassa  is  heated  with  a  great  excess  of  caustic  alkali  it 
is  converted,  as  already  remarked,'  into  carbonic  acid  and  light  carbonetted 
hydrogen,  by  the  reaction  of  the  oxygen  of  the  water  of  the  hydrate  upon 
the  carbon  of  the  acid. 

C4H303,H0  =  C204-f  C2H4. 


KAKODYL   AND   ITS    COMPOUNDS. 


The  substance  long  known  under  the  name  of  fuming  liquor  of  Cadet,  pre- 
pared by  distilling  a  mixture  of  dry  acetate  of  potassa  and  arsenious  acid» 
has  been  shown  by  M.  Bunsen  to  be  the  oxide  of  an  isolable  organic  basyl, 
capable  of  forming  a  vast  number  of  combinations,  displacing  other  bodies, 
and  being  in  turn  displaced  by  them,  in  the  same  manner  as  a  metal.  The 
investigation  of  this  difficult  subject  reflects  the  highest  honour  on  the  pa- 
tience and  skill  of  the  discoverer.  Kakodyl,  so  named  from  its  poisonous 
and  off^ensive  nature,  contains  three  elements,  viz.,  carbon,  hydrogen,  and 
arsenic. 

Table  of  the  most  important  Kakodyl- Compounds. 

Kakodyl  (symbol  Kd) C4H6AS. 

Oxide  of  kakodyl  KdO. 

Chloride  of  kakodyl KdCl. 

Chloride  of  kakodyl  and  copper  KdCl-j-CugCl. 

Oxy-chloride  of  kakodyl  3KdCl-f-KdO. 

Terchloride  of  kakodyl KdClg. 

Bromide  of  kakodyl KdBr. 

Iodide  of  kakodyl  Kdl. 

Cyanide  of  kakodyl KdCy. 

Kakodylic  acid KdOg. 

Kakodylate  of  silver  AgO,Kd03. 

Kakodylate  of  kakodyl  KdO.KdOg. 

Sulphide  of  kakodyl KdS. 

Sulphide  of  kakodyl  and  copper KdS-f-3CuS. 

Tersulphide  of  kakodyl  KdSg. 

Sulphur-salts  containing  tersulphide  \  KdS.KdSs— AuS,KdS3. 

of  kakodyl  /  CuS,KdS3— PbS,KdSj. 

Selenide  of  kakodyl KdSe. 

Oxide  op  kakodyl;  Cadet's  ruMiNa  liquid  ;  alkarsin  ;  KdO. — Equal 
^eights  of  acetate  of  potassa  and  arsenious  acid  are  intimately  mixed,  and 
introduced  into  a  glass  retort  connected  with  a  condenser  and  tubulated  re- 
ceiver, cooled  by  ice :  a  glass  tube  is  attached  to  the  receiver  to  carty  away 
the  permanently-gaseous  products  to  some  distance  from  the  experimenter. 

»  See  page  153. 


S78  KAKODYL     AND     ITS     COMPOUNDS. 

Heat  is  then  applied  to  the  retort,  which  is  gradually  increased  to  redness. 
At  the  close  of  the  operation,  the  receiver  is  found  to  contain  two  liquids, 
besides  a  quantity  of  reduced  arsenic :  the  heavier  of  these  is  the  oxide  of 
kakodyl  in  a  coloured  and  impure  condition ;  the  other  chiefly  consists  of 
water,  acetic  acid,  and  acetone.  The  gas  given  off  during  distillation  is 
principally  carbonic  acid.  The  crude  oxide  of  kakodyl  is  repeatedly  washed 
by  agitation  with  water,  previously  freed  from  air  by  boiling,  and  afterwards 
re-distilled  from  hydrate  of  potassa  in  a  vessel  filled  with  pure  hydrogen  gas. 
All  these  operations  must  be  conducted  in  the  open  air,  and  the  strictest  pre- 
cautions adopted  to  avoid  the  accidental  inhalation  of  the  smallest  quantity 
of  the  vapour  or  its  products. 

Oxide  of  kakodyl  is  a  colourless,  ethereal  liquid  of  great  refractive  power ; 
it  is  much  heavier  than  water,  having  a  density  of  1-462.  It  is  very  slightly 
soluble  in  water,  but  easily  dissolved  by  alcohol ;  its  boiling-point  approaches 
302°  (150°C),  and  it  solidifies  to  a  white  crystalline  mass  at  9°  r  — 12°-6C). 
The  odour  of  this  substance  is  extremely  offensive,  resembling  that  of  arse- 
netted  hydrogen :  the  minutest  quantity  attacks  the  eyes  and  the  mucous 
membrane  of  the  nose ;  a  larger  dose  is  highly  dangerous.  When  exposed 
to  the  air,  oxide  of  kakodyl  emits  a  dense  white  smoke,  becomes  heated,  and 
eventually  takes  fire,  burning  with  a  pale  flame,  and  producing  carbonic  acid, 
water,  and  a  copious  cloud  of  arsenious  acid.  It  explodes  when  brought  into 
contact  with  strong  nitric  acid,  and  inflames  spontaneously  when  thrown  into 
chlorine  gas.  The  density  of  the  vapour  of  this  body  is  about  7-5.  Oxide 
of  kakodyl  is  generated  by  the  reaction  of  arsenious  acid  on  the  elements  of 
acetone,  carbonic  acid  being  at  the  same  time  formed ;  the  accompanying 
products  are  accidental : — 

2  eq.  acetone  CgHgOg,  and  1  eq.  arsenious  acid,  AsOgssrI  eq.  oxide  kakodyl, 
C4HgAsO,  and  2  eq.  carbonic  acid,  C2O4. 

Chlobide  of  Kakodyl,  KdCl.  —  A  dilute  alcoholic  solution  of  oxide  of 
kakodyl  is  cautiously  mixed  with  an  equally  dilute  solution  of  corrosive 
sublimate,  avoiding  an  excess  of  the  latter ;  a  white,  crystalline,  inodorous 
precipitate  falls,  containing  KdO-}-2HgCl;  when  this  is  distilled  with  con- 
centrated liquid  hydrochloric  acid,  it  yields  corrosive  sublimate,  water,  and 
chloride  of  kakodyl,  which  distils  over.  The  product  is  left  some  time  in 
contact  with  chloride  of  calcium  and  a  little  quicklime,  and  then  distilled 
alone  in  an  atmosphere  of  carbonic  acid.  The  pure  chloride  is  a  colourless 
liquid,  which  does  not  fume  in  the  air,  but  emits  a  vapour  even  more  fearful 
in  its  effects,  and  more  insupportable  in  odour  than  that  of  the  oxide.  It  is 
heavier  than  water,  and  insoluble  in  that  liquid,  as  also  in  ether ;  alcohol,  on 
the  other  hand,  dissolves  it  with  facility.  The  boiling-point  of  this  compound 
is  a  little  above  212°  (100°C) ;  its  vapour  is  colourless,  is  spontaneously  in= 
flammable  in  the  air,  and  has  a  density  of  4-56.  Dilute  nitric  acid  dissolves 
the  chloride  without  change ;  with  the  concentrated  acid  ignition  and  explo- 
sion occur.  Chloride  of  kakodyl  combines  with  subchloride  of  copper  to  a 
white,  insoluble,  crystalline  double  salt,  containing  KdCl-f-CugCl,  and  also 
with  oxide  of  kakodyl. 

Kakodyl,  in  a  free  state,  may  be  obtained  by  the  action  of  metallic 
zinc,  iron,  or  tin  upon  the  above-described  compound.  Pure  and  anhydrous 
chloride  of  kakodyl  is  digested  for  three  hours,  at  a  temperature  of  212° 
(100°C),  with  slips  of  clean  metallic  zinc  contained  in  a  bulb  blown  upon  a 
glass  tulje,  previously  filled  with  carbonic  acid  gas,  and  hermetically  sealed. 
The  metal  dissolves  quietly  without  evolution  of  gas.  When  the  action  is 
complete,  and  the  whole  cool,  the  vessel  is  observed  to  contain  a  white  saline 
mass,  which  on  the  admission  of  a  little  water  dissolves,  and  liberates  a 
heavy  oily  liquid,  the  kakodyl  itself.  This  is  rendered  quite  pure  by  distil- 
lation from  a  fresh  quantity  of  zinc,  the  process  being  conducted  in  the  little 


KAKODYL    AND     ITS     COMPOUNDS.  379 

apparatus  shown  in  the  margin  (fig.  170),  which  is  made  Fig.lTO. 

from  a  piece  of  glass  tube,  and  is  intended  to  serve  the  pur- 
pose both  of  retort  and  receiver.  The  zinc  is  introduced 
into  the  upper  bulb,  and  then  the  tube  drawn  out  in  the 
manner  represented.  The  whole  is  then  filled  with  carbonic 
acid,  and  the  lower  extremity  put  into  communication  with 
a  little  hand-syringe.  On  dipping  the  point  a  into  the  crude 
kakodyl  and  making  a  slight  movement  of  exhaustion,  the 
liquid  is  drawn  up  into  the  bulb.  Both  extremities  are 
then  sealed  in  the  blow-pipe  flame,  and  after  a  short  diges- 
tion at  212°  (100°C)  or  a  little  above,  the  pure  kakodyl  is 
distilled  off  into  the  lower  bulb,  which  is  kept  cool.  It 
forms  a  colourless,  transparent,  thin  liquid,  much  resemb- 
ling the  oxide  in  odour,  and  surpassing  that  substance  in 
inflammability.  When  poured  into  the  air,  or  into  oxygen 
gas,  it  ignites  instantly ;  the  same  thing  happens  with  chlo- 
rine. With  very  limited  access  of  air  it  throws  off  white  fumes,  passing  into 
oxide,  and  eventually  into  kakodylic  acid.  Kakodyl  boils  at  338°  (170°C), 
and  when  cooled  to  21°  ( — 6°-lC)  crystallizes  in  large,  transparent,  square 
prisms.  It  combines  directly  with  sulphur  and  chlorine,  and  in  fact  may 
readily  be  made  to  furnish  all  the  compounds  previously  derived  from  th© 
oxide.  It  constitutes  the  most  perfect  type  of  an  organic  quasi-metal  which 
chemistry  yet  possesses. 

Kakodyl  is  decomposed  by  a  temperature  inferior  to  redness  into  metallic 
arsenic,  and  a  mixture  of  2  measures  light  carbonetted  hydrogen,  and  1 
measure  defiant  gas. 

Chloride  of  kakodyl  forms  a  hydrate,  which  is  thick  and  viscid,  and  readily 
decomposable  by  chloride  of  calcium,  which  withdraws  the  water.  In  the 
preparation  of  the  chloride,  and  also  in  other  operations,  a  small  quantity  of 
a  red  amorphous  powder  is  often  obtained,  called  erytrarsin.  This  is  inso- 
luble in  water,  alcohol,  ether,  and  caustic  potassa,  but  is  gradually  oxidized 
by  exposure  to  the  air,  with  production  of  arsenious  acid.      It   contains 

C^HeOgASg. 

Iodide  of  kakodyl,  Kdl.  —  This  is  a  thin,  yellowish  liquid,  of  offensive 
odour,  and  considerable  specific  gravity,  prepared  by  distilling  oxide  of 
kakodyl  with  strong  solution  of  hydriodic  acid,  A  yellow  crystalline  sub- 
stance is  at  the  same  time  formed,  which  is  an  oxy-iodide.  Bromide  and 
jiuoride  of  kakodyl  have  likewise  been  obtained  and  examined. 

Sulphide  of  kakodyl,  KdS,  is  prepared  by  distilling  chloride  of  kakodyl 
with  a  solution  of  the  bisulphide  of  barium  and  hydrogen.  It  is  a  clear,  thin, 
colourless  liquid,  smelling  at  once  of  alkarsin  and  mercaptan,  insoluble  in 
water,  and  spontaneously  inflammable  in  the  air.  Its  boiling-point  is  high, 
but  it  distils  easily  with  the  vapour  of  water.  This  substance  dissolves 
sulphur,  and  generates  tersulphide  of  kakodyl,  KdSj,  which  is  a  sulphui-- 
acid,  and  combines  with  the  sulphides  of  gold,  copper,  bismuth,  lead,  and 
antimony. 

Cyanide  of  kakodyl,  KdCy.  —  The  cyanide  is  easily  formed  by  distilling 
alkarsin  with  strong  hydrocyanic  acid,  or  cyanide  of  mercury.  Above  91" 
(32°-7C)  it  is  a  colourless,  ethereal  liquid,  but  below  that  temperature  it 
crystallizes  in  colourless,  four-sided  prisms,  of  beautiful  diamond  lustre.  It 
boils  at  about  284°  (140°C),  and  is  but  slightly  soluble  in  water.  It  requii-es 
to  be  heated  before  inflammation  occurs.  The  vapour  of  tlfis  substance  is 
most  fearfully  poisonous  ;  the  atmosphere  of  a  room  is  said  to  be  so  far  con- 
taminated by  the  evaporation  of  a  few  grains,  as  to  cause  instantaneous 
numbness  of  the  hands  and  feet,  vertigo,  and  even  unconsciousness. 

Kakodylic  acid  (alkargen)  ;  KdOj.— This  is  the  ultimate  product  of  th« 


SSO  KAKODYL     AND     ITS    COMPOUNDS. 

action  of  oxygen  at  a  low  temperature  upon  kakodyl  or  its  oxide  ;  it  is  best 
prepared  by  adding  oxide  of  mercury  to  that  substance,  covered  with  a  layer 
of  water,  and  artificially  cooled,  until  the  mixture  loses  all  odour,  and  after- 
wards decomposing  any  kakodylate  of  mercury,  that  may  have  been  formed, 
by  the  cautious  addition  of  more  alkarsin.  The  liquid  furnishes,  by  evapo- 
ration to  dryness  and  solution  in  alcohol,  crystals  of  the  new  acid.  The 
sulphide,  and  other  compounds  of  kakodyl,  yield,  by  exposure  to  air,  the 
same  substance.  Kakodylic  acid  forms  brilliant,  colourless,  brittle  crystals, 
which  have  the  form  of  a  modified  square  prism  ;  it  is  permanent  in  dry  air, 
but  deliquescent  in  a  moist  atmosphere.  It  is  very  soluble  in  water  and  in 
alcohol,  but  not  in  ether ;  the  solution  has  an  acid  reaction.  "When  mixed 
with  alkalis  and  evaporated,  a  gummy,  amorphous  mass  results.  With  the 
oxides  of  silver  and  mercury,  on  the  other  hand,  it  yields  crystallizable  com- 
pounds. It  unites  with  oxide  of  kakodyl,  and  forms  a  variety  of  combinations 
with  metallic  salts.  Alkargen  is  exceedingly  stable ;  it  is  neither  affected  by 
red,  fuming  nitric  acid,  aqua  regia,  nor  even  chromic  acid  in  solution ;  it 
may  be  boiled  with  these  substances  without  the  least  change.  It  is  deoxi- 
dized, however,  by  phosphorous  acid  and  protochloride  of  tin  to  oxide  of 
kakodyl.  Dry  hydriodic  acid  gas  decomposes  it,  with  production  of  water, 
iodide  of  kakodyl,  and  free  iodine ;  hydrochloric  acid,  under  similar  circum- 
stances, converts  it  into  a  corresponding  terchloride,  which  is  solid  and  crys- 
tallizable. Lastly,  what  is  extremely  remarkable,  this  substance  is  not  in 
the  least  degree  poisonous. 

Parakakodylic  oxide.  —  When  air  is  allowed  access  to  a  quantity  ot 
alkarsin,  so  slowly  that  no  sensible  rise  of  temperature  follows,  that  body  is 
gradually  converted  into  a  thick  syrupy  liquid,  full  of  crystals  of  kakodylic 
acid.  Long  exposure  to  air,  or  the  passage  of  a  copious  current  through  the 
mass,  heated  to  158°  (70°C),  fails  to  induce  crystallization  of  the  whole.  If 
in  this  state  water  be  added,  everything  dissolves,  and  a  solution  results 
which  contains  kakodylic  acid,  partly  free,  and  partly  in  combination  with 
the  oxide  of  kakodyl.  When  this  liquid  is  distilled,  water,  having  the  odour 
of  alkarsin,  passes  over,  and  afterwards  an  oily  liquid,  which  is  the  new 
compound.     Impure  kakodylic  acid  remains  in  the  retort. 

Parakakodylic  oxide,  purified  by  rectification  from  caustic  baryta,  is  a 
colourless,  oily  liquid,  strongly  resembling  alkarsin  itself  in  odour,  relations 
to  solvents,  and  in  the  great  number  of  its  reactions.  It  neither  fumes  in 
the  air,  however,  nor  takes  fire  at  common  temperatures ;  its  vapour,  mixed 
with  air,  and  heated  to  190°  (87°-8C),  explodes  with  violence.  By  analysis, 
U  is  found  to  have  exactly  the  same  composition  as  ordinary  oxide  of  kakodjil. 


WOOD-SPIRIT    AND    ITS    DERIVATIVES.  881 


SECTION  II. 

SUBSTANCES  MORE  OR  LESS  ALLIED  TO  ALCOHOL. 


WOOD-SPIEIT   AND   ITS    DERIVATIVES. 

In  the  year  1812,  Mr.  P.  Taylor  discovered,  among  the  liquid  products 
of  the  destructive  distillation  of  dry-wood,  a  peculiar  volatile  inflammable 
liquid,  much  resembling  spirit  of  wine,  to  which  allusion  has  already  been 
made.  This  substance  has  been  shown  by  MM.  Dumas  and  Peligot  to  be 
really  a  second  alcohol,  forming  an  ether,  and  a  series  of  compounds,  exactly 
corresponding  with  those  of  vinous  spirit,  and  even  more  complete,  in  some 
points,  than  the  latter.  Wood-spirit,  like  ordinary  alcohol,  may  be  regarded 
as  a:  hydrated  oxide  of  a  body  like  ethyl,  containing  C2H3,  called  methyls 

A  very  great  number  of  compound  methyl-ethers  have  been  described; 
they  present  the  most  complete  parallelism  of  origin,  properties,  and  consti- 
tution with  those  derived  from  common  alcohol. 

Wood-spirit  Series. 

Methyl  (symbol,  Me) CjHj 

Oxide  of  methyl CgHgO 

Hydride  of  methyl  (marsh  gas) CgHjH 

Chloride  of  methyl CgHgCl 

Iodide  of  methyl  &c GgHgl 

Zinc-methyl CgHgZn 

Wood-spirit CgHgO.HO 

Sulphate  of  oxide  of  methyl CaHgOjSOg 

Nitrate  of  oxide  of  methyl  &c CgHjO.NOg 

Sulphomethylic  acid C2H30,2S08,HO 

Formic  acid CjH  Og.HO 

Chloroform CgH  CI,, 

Hydrated  oxide  op  methyl;  pyroxylic  spirit;  wood-spirit;  MeO,HO 
— The  crude  wood-vinegar  probably  contains  about  j^^  part  of  this  sub 
stance,  which  is  separated  from  the  great  bulk  of  the  liquid  by  subjecting 
the  whole  to  distillation,  and  collecting  apart  the  first  portions  which  pass 
over.  The  acid  solution  thus  obtained  is  neutralized  by  hydrate  of  lime,  the 
clear  liquid  separated  from  the  oil  which  floats  on  the  surface,  and  from  the 
sediment  at  the  bottom  of  the  vessel,  and  again  distilled.  A  volatile  liquid, 
which  burns  like  weak  alcohol,  is  obtained ;  this  may  be  strengthened  in  the 
same  manner  as  ordinary  spirit,  by  rectification,  and  ultimately  rendered 
pure  and  anhydrous,  by  careful  distillation  from  quick-lime  by  the  heat  of  a 
water-bath.  Pure  wood-spirit  is  a  colourless,  thin  liquid,  of  peculiar  odour, 
quite  different  from  that  of  alcohol,  and  burning,  disagreeable  taste ;  it  boils 

'  From  iJiiQv,  wine,  and  i\rj,  wood ;  the  termination  v\^,  or  yl,  is  very  frequently, 
employed  in  the  sjd9>  of  matter,  material. 


382  WOOD-SPIRIT     AND     ITS     DERIVATIVES. 

at  152°  (66°-6C),  and  has  a  density  of  0-798  at  68°  (20C).  The  dsnsity  of 
its  vapour  is  1-12.  Wood-spirit  mixes  in  all  proportions  with  water,  when 
pure ;  it  dissolves  resins  and  volatile  oils  as  freely  as  alcohol,  and  is  often 
substituted  for  alcohol  in  various  processes  in  the  arts,  for  which  purpose  it 
is  prepared  on  a  large  scale.  It  may  be  burned  instead  of  ordinary  spirit, 
in  lamps ;  the  flame  is  pale-coloured,  like  that  of  alcohol,  and  deposits  no 
Boot.  Wood-spirit  dissolves  caustic  baryta ;  the  solution  deposits,  by  evapo- 
ration in  vacuo,  acicular  crystals,  containing  BaO-(-MeO,HO.  Like  alcohol, 
it  dissolves  chloride  of  calcium  in  large  quantity,  and  gives  rise  to  a  crystal- 
line compound,  resembling  that  formed  by  alcohol,  and  containing,  according 
to  Kane,  CaCl+2(MeO,HO). 

Oxide  of  methyl  ;  wood-ether  ;  MeO.  —  One  part  of  wood-spirit  and  4 
parts  of  concentrated  sulphuric  acid  are  mixed  and  exposed  to  heat  in  a 
flask  fitted  with  a  perforated  cork  and  bent  tube ;  the  liquid  slowly  blackens, 
and  emits  large  quantities  of  gas,  which  may  be  passed  through  a  little 
strong  solution  of  caustic  potassa,  and  collected  over  mercury.  This  is  the 
wood-spirit  ether,  a  permanently  gaseous  substance,  which  does  not  liquefy  at 
the  temperature  of  3°  ( —  16°'1C).  It  is  colourless,  has  an  ethereal  odour, 
and  burns  with  a  pale  and  feebly  luminous  flame.  Its  specific  gravity  is 
1-617.  Cold  water  dissolves  about  36  times  its  volume  of  this  gas,  acquiring 
thereby  the  characteristic  taste  and  odour  of  the  substance ;  when  boiled, 
the  gas  is  again  liberated.  Alcohol,  wood-spirit,  and  concentrated  sulphuric 
acid,  dissolve  it  in  still  larger  quantity. 

Under  the  head  of  ether  it  has  been  mentioned  that  the  generally  received 
relation  of  this  substance  to  the  other  ethyl-compounds  had  been  rendered 
doubtful  by  recent  researches.  The  same  remark  of  course  applies  to  me- 
thylic  ether,  which  is  in  every  respect  analogous  to  common  ethers.  It  was 
first  proposed  by  Berzelius,  and  has  long  been  urged  by  MM.  Laurent  and 
Gerhardt,  that  the  composition  of  alcohol  being  expressed  by  the  formula 
^4^6^2'  *^®  *''^®  formula  of  ether  was  CgHjoOg,  and  not  C4H5O.  The  cor- 
rectness of  this  view  has  lately  been  established  by  a  series  of  beautiful  ex- 
periments carried  out  by  Prof.  Williamson.  lie  found  that  the  substance 
produced  by  dissolving  potassium  in  alcohol,  which  has  the  formula  C^IIjO, 
KO,  when  acted  upon  by  iodide  of  ethyl,  furnishes  iodide  of  potassium  and 
perfectly  pure  ether.  This  reaction  may  be  expressed  by  the  two  following 
equations  :— 

C4H50,KO  -f  C4H5I  =  KI  -f  2C4II5O,  or 
C4H50,K0  -f  C4H5I  =  KI  -f-    C«H,„02. 

Tiat  in  this  reaction,  not  two  equivalents  of  ether,  as  represented  in  the 
first  equation,  but  a  compound  CgHjoOg  is  formed,  as  expressed  in  the  second, 
is  clearly  proved  by  substituting,  when  acting  upon  the  compound  C4H50,K0, 
for  the  iodide  of  ethyl,  the  corresponding  methyl-compound.  In  this  case 
neither  common  ether  nor  methyl-ether  is  formed,  but  an  intermediate  com- 
pound CgHgOj  =  041150,021130.  This  substance  is  insoluble  in  water,  and 
has  a  peculiar  odour  similar  to  that  of  ether,  but  boils  at  50°  (10°C). 

It  is  very  probable  tliat  the  substances,  which  have  been  described  by 
the  terms  ethyl  and  methyl,  likewise  are  not  C4H5  and  CjHg,  but  CgH,Q  and 
C4Hg.  The  limits  of  this  elementary  work  will  not  permit  us  to  enter  into 
the  details  of  this  question,  which  is  still  under  the  discussion  of  scientific 
chemists. 

Chloride  of  methyl,  MeCl.  —  This  compound  is  most  easily  prepared  by 
heating  a  mixture  of  2  parts  of  common  salt,  1  of  wood-spirit,  and  3  of  con- 
centrated sulphuric  acid ;  it  is  a  gaseous  body,  which  may  be  conveniently 
collected  over  water,  as  it  is  but  slightly  soluble  in  that  liquid.  Chloride  of 
methyl  is  colourless ;  it  has  a  peculiar  odour  and  sweetish  taste,  and  bum^ 


WOOD-SPIRIT    AND     ITS     DERIVATIVES.  883 

when  kindled,  with  a  pale  flame,  greenish  towards  the  edges,  like  most  com- 
bustible chlorine-compounds.  It  has  a  density  of  1*731,  and  is  not  liquefied 
at  0°  ( — 17°-7C).  The  gas  is  decomposed  by  transmission  through  a  red-hot 
tube,  with  slight  deposition  of  carbon,  into  hydrochloric  acid  gas  and  a  car- 
bonetted  hydrogen,  which  has  been  but  little  examined. 

Iodide  of  methyl,  Mel,  is  a  colourless  and  feebly  combustible  liquid, 
obtained  by  distilling  together  1  part  of  phosphorus,  8  of  iodine,  and  12  or 
15  of  wood-spirit.  It  is  insoluble  in  water,  has  a  density  of  2-257,  and 
boils  at  111°  (430-8C).  The  density  of  its  vapour  is  4-883.  The  action  of 
zinc  upon  iodide  of  methyl  in  sealed  tubes  furnishes  a  colourless  gas,  appa- 
rently a  mixture  of  several  substances,  among  which  methyl  may  occur.* 
The  residue  contains  iodide  of  zinc  together  with  a  volatile  substance  of  very 
disagreeable  odour,  which  absorbs  oxygen  with  so  much  avidity,  that  it  takes 
fire  when  coming  in  contact  with  the  air.  It  is  zinc-methyl,  C4H5Zn,  cor- 
responding to  zinc-ethyl.  (See  page  368.)  "When  mixed  with  water  it  yields 
oxide  of  zinc  and  light  carbonetted  hydrogen. 

Cyanide  op  methyl,  MeCy.  —  If  a  dry  mixture  of  sulphomethylate  of 
baryta  and  cyanide  of  potassium  are  heated  in  a  retort,  a  very  volatile  liquid 
of  a  powerful  odour  distils  over.  It  generally  contains  hydrocyanic  acid  and 
water,  from  which  it  is  separated  by  distillation,  first  over  red  oxide  of  mer- 
cury, and  then  over  anhydrous  phosphoric  acid.  When  thus  purified,  it  has 
an  agreeable  aromatic  odour,  and  boils  at  170°-6  (77°C).  When  boiled  with 
potassa,  it  undergoes  a  decomposition  analogous  to  that  of  cyanide  of  ethyl, 
(see  page  354)";  it  absorbs  4  eq.  of  water,  and  yields  acetic  acid  and  am- 
monia. 

MeCy  =  C.HgN  I  C4H30,HO  =  C.H^     O4 


C4H,N04  I  C4H,N04 

It  has  been  mentioned  that  this  compound  may  be  obtained  by  abstracting 
4  eq.  of  water  from  acetate  of  ammonia  by  means  of  phosphoric  acid.  (See 
(page  373.) 

Compounds  of  methyl  with  bromine,  fluorine,  and  sulphur  have  also  been 
obtained. 

Sulphate  of  oxide  of  methyl,  MeO,S03.  —  This  interesting  substance  is 
prepared  by  distilling  1  part  of  wood-spirit  with  8  or  10  of  strong  oil  of 
vitriol :  the  distillation  may  be  carried  nearly  to  dryness.  The  oleaginous 
liquid  found  in  the  receiver  is  agitated  with  water,  and  purified  by  rectifica- 
tion from  powdered  caustic  baryta.  The  product,  which  is  the  body  sought, 
is  a  colourless  oily  liquid,  of  alliaceous  odour,  having  a  density  of  1-324,  and 
boiling  at  370°  (187°7C).  It  is  neutral  to  test-paper,  and  insoluble  in  water, 
but  decomposed  by  that  liquid,  slowly  in  the  cold,  rapidly  and  with  violence 
at  a  boiling  temperature,  into  sulphomethylic  acid  and  wood-spirit,  which  is 
thus  reproduced  by  hydration  of  the  liberated  methylic  ether.  Anhydrous 
lime  or  baryta  have  no  action  on  this  summit;  their  hydrates,  however,  and 
those  of  potassa  and  soda,  decompose  it  instantly,  with  production  of  a  sul 
phomethylate  of  the  base,  and  wood-spirit.  When  neutral  sulphate  of  methyl 
is  heated  with  common  salt,  it  yields  sulphate  of  soda  and  chloride  of  methyl ; 
with  cyanide  of  mercury  or  potassium,  it  gives  a  sulphate  of  the  base,  and 
cyanide  of  methyl ;  with  dry  formate  of  soda,  sulphate  of  soda  and  formate 
of  methyl.    These  reactions  possess  great  interest. 

*  The  same  compound  is  believed  to  occur  among  the  substances  produced  by  the  action  of 
a  galvanic  current  upon  acetic  acid.    See  valerianic  acid,  page  S92. 


«J84  WOOD-SPIRIT   AND    ITS    DERIVATIVES. 

Nitrate  of  oxide  of  jiethyl,  MeOjNOg.  —  One  part  of  nitrate  of 
potassa  is  introduced  into  a  retort,  connected  with  a  tubulated  receiver,  to 
which  is  attached  a  bottle,  containing  salt  and  water,  cooled  by  a  freezing, 
mixture  ;  a  second  tube  serves  to  carry  oflF  the  incondensible  gases  to  a  chim- 
ney. A  mixture  of  one  part  of  wood-spirit  and  2  of  oil  of  vitriol  is  made,  and 
immediately  poured  upon  the  nitre  ;  reaction  commences  at  once,  and  requires 
but  little  aid  from  external  heat,  A  small  quantity  of  red  vapour  is  seen  to 
arise,  and  an  ethereal  liquid  condenses,  in  great  abundance,  in  the  receiver, 
and  also  in  the  bottle.  When  the  process  is  at  an  end,  the  distilled  products 
are  mixed,  and  the  heavy  oily  liquid  obtained  separated  from  the  water.  It 
is  purified  by  several  successive  distillations  by  the  heat  of  a  water-bath  from 
a  mixture  of  chloride  of  calcium  and  litharge,  and,  lastly,  rectified  alone  in  a 
retort,  furnished  with  a  thermometer  passing  through  the  tabulature.  The 
liquor  begins  to  boil  at  about  140°  (60°C);  the  temperature  soon  rises  to 
150°  (65°'5C),  at  which  point  it  remains  constant;  the  product  is  then  col- 
lected apart,  the  first  and  most  volatile  portions  being  contaminated  with 
hydrocyanic  acid  and  other  impurities.  Even  with  these  precautions,  the 
nitrate  of  methyl  is  not  quite  pure,  as  the  analytical  results  show.  The  pro- 
perties of  the  substance,  however,  remeve  any  doubts  respecting  its  real 
nature. 

Nitrate  of  methyl  is  colourless,  neutral,  and  of  feeble  odour ;  its  density  is 
1-182;  it  boils  at  150°  (65°-5C),  and  burns,  when  kindled,  with  a  yellow 
flame.  Its  vapour  has  a  density  of  2-64,  and  is  eminently  explosive;  when 
heated  in  a  flask  or  globe  to  300°  (140°C),  or  a  little  above,  it  explodes  with 
fearful  violence ;  the  determination  of  the  density  of  the  vapour  is,  conse- 
quenth',  an  operation  of  danger.  Nitrate  of  methyl  is  decomposed  by  a  solu- 
tion of  caustic  potassa  into  nitrate  of  that  base  and  wood-spirit. 

Oxalate  of  oxide  of  methyl,  MeO,  CgOj.  —  This  beautiful  and  interest- 
ing substance  is  easily  prepared  by  distilling  a  mixture  of  equal  weights  of 
oxalic  acid,  wood-spirit,  and  oil  of  vitriol.  A  spirituous  liquid  collects  in  the 
receiver,  which,  exposed  to  the  air,  quickly  evaporates,  leaving  the  oxalic 
methyl-ether  in  the  form  of  rhombic  transparent  crystalline  plates,  which 
may  be  purified  by  pressure  between  folds  of  bibulous  paper,  and  re-distilled 
from  a  litlle  oxide  of  lead.  The  product  is  colourless,  and  has  the  odour  of 
common  oxalic  ether;  it  melts  at  124°  (51°'1C),  and  boils  at  322°  (161  °C). 
It  dissolves  freely  in  alcohol  and  wood-spirit,  and  also  in  water,  which,  how- 
ever, rapidly  decomposes  it,  especially  when  hot,  into  oxalic  acid  and  wood- 
spirit.  The  alkaline  hydrates  efl'ect  the  same  change  even  more  easily.  Solu- 
tion of  ammonia  converts  it  into  oxanide  and  wood-spirit.  With  dry  ammo- 
niacal  gas  it  yields  a  white,  solid  substance,  which  crystallizes  from  alcohol 
in  pearly  cubes ;  this  new  body,  designated  ozamethylane,  or  oxamate  of 
methyl,  contains  CgH5N06=C2H30,C4H2N05. 

Many  other  salts  of  oxide  of  methyl  have  been  formed  and  examined.  The 
acetate,  MeO,C4n30g,  is  abundantly  obtained  by  distilling  2  parts  of  wood- 
spirit  with  1  of  ci'ystallizable  acetic  acid,  and  1  of  oil  of  vitriol.  It  much 
resembles  acetic  ether,  having  a  density  of  0-919,  and  boiling  at  136°(57°-8C) ; 
the  density  of  its  vapour  is  2-563.  This  compound  is  isomeric  with  formic 
ether.  Formate  of  methyl,  MeO.CgHOj,  is  prepared  by  heating  in  a  retort 
equal  weights  of  sulphate  of  methyl  and  dry  formate  of  soda,  it  is  very  vola- 
tile, lighter  than  water,  and  is  isomeric  with  hydrate  of  acetic  acid.  Chloro- 
carbonic  methyl-ether  is  produced  by  the  action  of  that  gas  upon  wood-spirit ; 
it  is  a  colourless,  thin,  heavy,  and  very  volatile  liquid,  containing  C4H3CIO4 
ssCallgOjCgClOgv  It  yields  with  dry  ammonia  a  solid  crystallizable  substance, 
called  urethylane,  C4H5NO4.     (See  page  358.) 

Sulphomethylic  acid,  MeO,2S08,HO.  —  Sulphomethylate  of  baryta  is 
prepared  in  the  same  manner  as  the  sulphovinate ;  1  part  of  wood-spirit  is 


WOOD-SPIRIT     AND     ITS     DERIVATIVES.  385 

b1owi>  mixed  with  2  parts  of  concentrated  sulphuric  acid,  the  whole  heated 
to  ebullition,  and  left  to  cool,  after  which  it  is  diluted  with  water  and  neu- 
tralized with  carbonate  of  baryta.  The  solution  is  filtered  from  the  inso- 
luble sulphate,  and  evaporated,  first  in  a  water-bath,  and  afterwards  in  vacuo 
to  the  due  degree  of  concentration.  The  salt  crystallizes  in  beautiful  square 
colourless  tables,  containing  BaO,C2H30,2S03-f-2HO,  which  efiloresce  in  dry 
air,  and  are  very  soluble  in  water.  By  exactly  precipitating  the  base  from 
this  substance  by  dilute  sulphuric  acid,  and  leaving  the  filtered  liquid  to  eva- 
porate in  the  air,  hydrated  sulphomethylic  acid  may  be  procured  in  the  form 
of  a  sour,  syrupy  liquid,  or  as  minute  acicular  crystals,  very  soluble  in 
water  and  alcohol.  It  is  very  instable,  being  decomposed  by  heat  in  the 
same  manner  as  sulphovinic  acid.  Sulphomethylale  of  potassa  crystallizes  in 
small,  nacreous,  rhombic  tables,  which  are  deliquescent;  it  contains  KO, 
C2H30,2S03.     The  lead-salt  is  also  very  soluble. 

Formic  acid. — As  alcohol  by  oxidation  under  the  influence  of  finely-divided 
platinfum  gives  rise  to  acetic  acid,  so  wood-spirit,  under  similar  circumstan- 
ces, yields  a  peculiar  acid  product,  produced  by  the  substitution  of  2  eq.  of 
oxygen  for  2  eq.  of  hydrogen,  to  which  the  term /orm/c  is  given,  from  its  oc- 
currence in  the  animal  kingdom,  in  the  bodies  of  ants.  The  experiment 
may  be  easily  made  by  inclosing  wood-spirit  in  a  glass  jar  with  a  quantity 
of  platinum-black,  and  allowing  moderate  excess  of  air ;  the  spirit  is  gra- 
dually converted  into  formic  acid.  There  has  not  been  found  an  interme- 
diate product  corresponding  to  aldehyde.  Anhydrous  formic  acid,  as  in  the 
salts,  contains  CgHOg,  or  the  elements  of  2  eq.  carbonic  oxide,  and  1  eq.  water. 

Pure  hydrate  formic  acid,  C2H03,HO,  is  obtained  by  the  action  of  sulphu- 
retted hydrogen  on  dry  formate  of  lead.  The  salt,  reduced  to  fine  powder, 
is  very  gently  heated  in  a  glass  tube  connected  with  a  condensing  apparatus, 
through  which  a  current  of  dry  sulphuretted  hydrogen  gas  is  transmitted. 
It  forms  a  clear,  colourless  liquid,  which  fumes  slightly  in  the  air,  of  exceed- 
ingly penetrating  odour,  boiling  at  209°  (08°-5C),  and  crystallizing  in  large 
brilliant  plates  when  cooled  below  32°  (0°C).  The  sp.  gr.  of  the  acid  is 
1-235;  it  mixes  with  water  in  all  proportions;  the  vapour  is  inflammable, 
and  burns  with  a  blue  flame.  A  second  hydrate,  containing  2  eq.  of  water, 
exists;  its  density  is  1-11,  and  it  boils  at  223°  (106°-1C).  In  its  concen- 
trated form  this  acid  is  extremely  corrosive ;  it  attacks  the  skin,  forming  a 
blister  or  an  ulcer,  painful  and  difficult  to  heal.  A  more  dilute  acid  may  be 
prepared  by  a  variety  of  processes :  starch,  sugar,  and  many  other  organic 
substances  often  yield  formic  acid  when  heated  with  oxidizing  agents ;  a  con- 
venient method  is  the  following : — 1  part  of  sugar,  3  of  binoxide  of  manga- 
nese, and  2  of  water,  are  mixed  in  a  very  capacious  retort,  or  large  metal 
still;  3  parts  of  oil  of  vitriol,  diluted  with  an  equal  weight  of  water,  are 
then  added,  and  when  the  first  violent  efi^ervescence  from  the  disengagement 
of  carbonic  acid  has  subsided,  heat  is  cautiously  applied,  and  a  considerable 
quantity  of  liquid  distilled  over.  This  is  very  impure ;  it  contains  a  vola- 
tile oily  matter,  and  some  substance  which  communicates  a  pungency  not 
proper  to  formic  acid  in  that  dilute  state.  The  acid  lifjuid  is  neutralized 
with  carbonate  of  soda,  and  the  resulting  formate  purified  by  crystallization, 
and  if  needful,  by  animal  charcoal.  From  this,  or  any  other  of  its  saltSj 
solution  of  formic  acid  may  be  readily  obtained  by  distillation  with  dilute 
sulphuric  acid.  It  has  an  odour  and  taste  much  resembling  those  of  acetic 
acid,  reddens  litmus  strongly,  and  decomposes  the  alkaline  carbonates  with 
eff"ervescence. 

Another  process  for  making  formic  acid  consists  in  distilling  dry  oxalic 

acid,  mixed  with  its  own  weight  of  sand  or  pumice-stone  in  a  glass  retort. 

Carbonic  oxide  and  carbonic  acid  are  disengaged,  while  a  very  acid  liquid 

distils,  which  is  formic  aciJ  coutamiuated  with  a  small  quantity  of  oia-iy 

33 


y»d  WOOD-SPIRIT     AND     ITS    DERIVATIVES. 

acid.  By  redistilling  this  mixture  pure  distilled  formic  acid  is  obtained. 
This  process  yields  a  very  strong  acid,  but  only  a  small  quantity  in  pro- 
portion to  the  oxalic  acid  employed. 

Formic  acid,  in  quantity,  may  be  extracted  from  ants  by  distilling  the 
insects  with  water,  or  by  simply  macerating  them  in  the  cold  liquid. 

Formic  acid  is  readily  distinguished  from  acetic  acid  by  heating  it  with  a 
little  solution  of  oxide  of  silver  or  mercury ;  the  metal  is  reduced,  and  pre- 
cipitated in  a  pulverulent  state,  while  carbonic  acid  is  extricated ;  this  re- 
action is  sufficiently  intelligible.  The  protochloride  of  mercury  is  reduced, 
by  the  aid  of  the  elements  of  water,  to  calomel,  carbonic  acid  and  hydro- 
chloric acids  being  formed. 

The  most  important  salts  of  formic  acid  are  the  following :  —  Formate  of 
soda  crystallizes  in  rhombic  prisms  containing  2  eq.  of  water;  it  is  very  so- 
luble, and  is  decomposed  like  the  rest  of  the  salts  by  hot  oil  of  vitriol  with 
evolution  of  pure  carbonic  oxide.  Fused  with  many  metallic  oxides,  it 
causes  their  reduction.  Formate  of  potassa  is  with  difficulty  made  to  crys- 
tallize from  its  great  solubility.  Formate  of  ammonia  crystallizes  in  square 
prisms ;  it  is  very  soluble,  and  is  decomposed  by  a  high  temperature  into 
hydrocyanic  acid  and  water,  the  elements  of  which  it  contains,  NIl40,C2H08 
— 4H0=C2NH,  This  decomposition  is  perfectly  analogous  to  that  of 
acetate  of  ammonia,  see  page  373.  The  salts  of  baryta,  stroniia,  lime,  and 
magnesia  form  small  prismatic  crystals,  soluble  without  difficulty.  Formate 
of  lead  crystallizes  in  small,  diverging,  colourless  needles,  which  require  for 
solution  40  parts  of  cold  water.  The  formates  of  manganese,  protoxide  of 
iron,  zinc,  nickel,  and  cobalt,  are  also  crystallizable.  That  of  copper  is  very 
beautiful,  constituting  bright  blue,  rhombic  prisms  of  considerable  magni- 
tude. Formate  of  silver  is  white,  but  slightly  soluble,  and  decomposed  by 
the  least  elevation  of  temperature. 

Chlorofokm. — This  substance  is  produced,  as  already  remarked,  when  an 
aqueous  solution  of  caustic  alkali  is  made  to  act  upon  chloral.  It  may  be 
obtained  with  greater  facility  by  distilling  alcohol,  wood-spirit,  or  acetone 
with  a  solution  of  chloride  of  lime.  1  part  of  hydrate  of  lime  is  suspended 
in  24  parts  of  cold  water,  and  chlorine  passed  through  the  mixture  until 
nearly  the  whole  lime  is  dissolved.  A  little  more  hydrate  is  then  added  to 
restore  the  alkaline  reaction,  the  clear  liquid  mixed  with  1  part  of  alcohol 
or  wood-spirit,  and,  after  an  interval  of  24  hours,  cautiously  distilled  in  a 
very  spacious  vessel.  A  watery  liquid  containing  a  little  spirit  and  a  heavy 
oil  bollect  in  the  receiver ;  the  latter,  which  is  the  chloroform,  is  agitated 
with  water,  digested  with  chloride  of  calcium,  and  rectified  in  a  water-bath. 
It  is  a  thin,  colourless  liquid  of  agreeable  ethereal  odour,  much  resembling 
that  of  Dutch-liquid,  and  sweetish  taste.  Its  density  is  1  -48,  and  it  boils  at 
1410-8  (61  °C) ;  the  density  of  its  vapour  is  4-116.  Chloroform  is  with  diffi- 
culty kindled,  and  burns  with  a  greenish  flame.  It  is  nearly  insoluble  in 
water,  and  is  not  affected  1)y  concentrated  sulphuric  acid.  Alcoholic  solution 
of  potassa  decomposes  it  with  production  of  chloride  of  potassium  and  for- 
mate of  potassa. 

Chloroform  may  be  prepared  on  a  larger  scale  by  cautiously  distilling  to- 
gether  good  commercial  chloride  of  lime,  water  and  alcohol.  The  whole 
product  distils  over  with  the  first  portions  of  water,  so  that  the  operation 
may  be  soon  interrupted  with  advantage. 

This  substance  has  been  called  strongly  into  notice  from  its  remarkable 
effects  upon  the  animal  system  in  producing  temporary  insensibility  to  pain 
when  its  vapour  is  inhaled. 

Chloroform  contains  CjHClg;  it  is  changed  to  formic  acid  by  the  substitu- 
tion of  three  eq.  of  oxygen  for  the  three  eq.  of  chlorine  removed  by  the 
alkaline  metal. 


WOOD-SPIRIT    AND    ITS    DERIVATIVES.  387 

Bromoform,  CgHBrs,  is  a  heavy,  volatile  liquid,  prepared  by  a  similar  pro- 
cess, bromine  being  substituted  in  the  place  of  chlorine.  It  is  converted  by 
alkali  into  bromide  of  potassium  and  formate  of  potassa.  Iodoform,  C2HI3, 
is  a  solid,  yellow,  crystallizable  substance,  easily  obtained  by  adding  alco- 
holic solution  of  potassa  to  tincture  of  iodine,  avoiding  excess,  evaporating 
the  -whole  to  dryness,  and  treating  the  residue  with  water.  Iodoform  is 
nearly  insoluble  in  water,  but  dissolves  in  alcohol,  and  is  decomposed  by  al- 
kalis in  the  same  manner  as  the  preceding  compounds. 

FoRMOMETHYLAL. — This  is  a  product  of  the  (Ustillation  of  wood-spirit  with 
dilute  sulphuric  acid  and  binoxide  of  manganese.  The  distilled  liquid  is 
saturated  with  potassa,  by  which  the  new  substance  is  separated  as  a  light 
oily  fluid.  When  purified  by  rectification,  it  is  colourless,  and  of  agreeable 
aromatic  odour;  it  has  a  density  of  0-855,  boils  at  170°  (41°C),  and  is  com- 
pletely soluble  in  three  parts  of  water.  It  contains  CgHgO^.  It  corresponds 
to  acetal,  and  may  be  viewed  as  a  compound  of  2  eq.  of  ether,  with  1  eq. 
of  the  yet  unknown  aldehyde  of  the  methyl-series,  C^Hg04=2C2H30,C2H202. 

Metuyl-meecaptan  is  prepared  by  a  process  similar  to  that  recommended 
for  ordinary  mercaptan,  sulphomethylate  of  potassa  being  substituted  for 
the  sulphovinate  of  lime.  It  is  a  colourless  liquid,  of  powerful  alliaceous 
odour,  and  lighter  than  water ;  it  boils  at  68°  (20°C),  and  resembles  mer- 
captan in  its  action  on  red  oxide  of  mercury. 

Products  of  the  action  of  chlorine  on  the  compounds  of  methyl.  — 
Chlorine  acts  upon  the  methylic  compounds  in  a  manner  strictly  in  obedi- 
ence to  the  law  of  substitution ;  the  carbon  invariably  remains  intact,  and 
every  proportion  of  hydrogen  removed  is  replaced  by  an  equivalent  quantity 
of  chlorine.  Methylic  ether  and  chlorine,  in  a  dry  and  pure  condition, 
yield  a  volatile  liquid  product,  containing  C2H2CIO ;  the  experiment  is  at- 
tended with  great  danger,  as  the  least  elevation  of  temperature  gives  rise  to 
a  violent  explosion.  This  product  in  its  turn  furnishes,  by  the  continued 
action  of  the  gas,  a  second  liquid,  containing  CaHCljO.  The  whole  of  the 
hydrogen  is  eventually  lost,  and  a  third  compound,  CgClgO,  produced. 

.  Chloride  of  methyl,  CgHgCl,  in  like  manner  gives  rise  to  three  successive 
products.  The  first,  CgHgClg,  is  a  new  volatile  liquid,  much  resembling 
chloride  of  olefiant  gas ;  the  second,  CgHClg,  is  no  other  than  chloroform ; 
the  third  is  bichloride  of  carbon,  C2CI4. 

Some  of  these  substances,  especially  chloroform  and  bichloride  of  carbon, 
have  been  obtained  also  by  the  action  of  chlorine  on  light  carbonetted  hy- 
drogen (marsh-gas),  which  thus  becomes  connected  with  the  methyl-series. 
It  may  be  regarded  as  hydride  of  methyl,  a  view  which  is  likewise  sup- 
ported by  its  formation  from  zinc-methyl  (see  page  382) ;  thus  we  have  the 
following  series. 

Hydride  of  methyl CgHgH.  Light  carbonetted  hydrogen. 

Chloride  of  methyl CjHgCl. 

Chlorinetted  chloride  of  methyl  CgHgCla-  * 

Bichlorinetted    "  «'        CgHClg.  Chloroform. 

Trichlorinetted  «  "         GfX^.  Bichloride  of  carbon. 

The  acetate  of  methyl,  C6H6O4,  gives  CgH4Cl204,  and  C6n3Cl304 ;  the  other 
methyl*ethers  are  without  doubt  affected  in  a  similar  manner. 

Commercial  wood-spirit  is  very  frequently  contaminated  with  other  sub- 
stances, some  of  which  are  with  great  difficulty  separated.  It  sometimes 
contains  aldehyde,  often  acetone  and  propioue,  and  very  frequently  a  vola- 
tile  oil,  which  is  precipitated  by  the  addition  of  water,  rendering  the  whole 
turbid.  The  latter  is  a  mixture  of  several  hydrocarbons,  very  analogous  to 
those  contained  in  coal-tar.  A  specimen  of  wood-spirit,  from  Wattwyl,  in 
Switzerland,  wq,s  found  by  Gmeliu  to  contain  a  volatile  lifiuid,  differing  in 


388  POTATO-OIL    AND    ITS    D  ER  I  V  A  T  I  "V  E  S  . 

some  respects  from  acetone,  to  which  he  gave  the  term  lignone.  A  verj 
similar  substance  is  described  by  Schwcizer  and  Weidmann,  under  the 
name  of  xylite.  Lastly,  Mr.  Scanlan  has  obtained  from  wood-spirit  a  solid, 
yellowish-red,  crystallizable  substance  called  eblanin.  It  is  left  behind  in 
the  retort  when  the  crude  spirit  is  rectified  from  lime ;  it  is  insoluble  in 
water,  sublimes  without  fusion  at  273°  (133°-9C),  and  contains,  according 
to  Dr.  Gregory,  C2iH904. 

POTATO-OIL   AND   ITS    DERIVATIVES. 

In  the  manufacture  of  potato-brandy  the  crude  spirit  is  found  to  be  con- 
taminated with  an  acrid  volatile  oil,  called  fusel-oil,  which  is  extremely  diffi- 
cult to  separate  in  a  complete  manner.  Towards  the  end  of  the  distillation, 
it  passes  over  in  considerable  quantity ;  it  may  be  collected  apart,  agitated 
with  several  successive  portions  of  water  to  withdraw  the  spirit,  with  which 
it  is  mixed,  and  re- distilled.  According  to  the  researches  of  M.  Cahours, 
this  substance  exhibits  properties  indicative  of  a  constitution  analogous  to 
that  of  alcohol ;  it  may  be  considered  as  the  hydrate  of  the  oxide  of  the 
hydrocarbon,  called  amyl,  containing  C,oH,j.  The  ether  of  potato-oil,  and 
a  variety  of  other  compounds,  corresponding  in  every  point  to  those  of  ordi- 
nary alcohol,  have  been  formed,  as  will  be  manifest  from  an  inspection  of 
the  following  table : — 

Amyl  (symbol  Ayl) ^lo^n 

Amyl-ether  C,qHj,0 

Hydride  of  amyl CiqHjjH 

Potato-oil  CiqH,, 0,110 

Chloride  of  amyl C,oH,,Cl 

Bromide  of  amyl CioH,,Br 

Iodide  of  amyl C,gH,iI 

Zinc-amyl  CioH,jZn 

Acetate  of  amyl C,oH,jO,C4H303 

Sulphamylic  acid CioHijO,2S03,HO 

Amylene ^xo^io 

Valerianic  acid CjoHgOg.HO. 

Hydrated  oxide  op  amyl;  fusel  oil;  AylO,HO. —  The  crude  fusel-oil 
of  potato-brandy  is  washed  with  water,  and  distilled  in  a  retort  furnished 
with  a  thermometer,  the  bulb  of  which  dips  into  the  liquid.  The  portion 
which  distils  between  260°  (12G°-6C)  and  280°  (137° -80)  is  collected  apart 
and  re-distilled  in  the  same  manner,  until  an  oil  is  obtained,  having  a  fixed 
boiling-point  at  268°  — 269°  (131°-1C— 131°-7C).  Thus  purified,  it  is  a 
thin  fluid  oil,  exhaling  a  powerful  and  peculiarly  suffocating  odour,  and 
leaving  a  burning  taste ;  it  inflames  with  some  difficulty,  and  then  burns 
with  a  pure  blue  flame.  Its  density  is  0-818,  It  undergoes  little  change  by 
contact  with  air  under  ordinary  circumstances;  but  when  warmed,  and 
dropped  upon  platinum-black,  it  oxidizes  to  valerianic  acid,  which  bears  the 
same  relation  to  this  substance  that  acetic  acid  does  to  ordinary  alcohol,  or 
formic  acid  to  methyl-alcohol. 

The  action  of  heat  upon  fusel-oil  has  been  lately  studied  by  Captain 
Reynolds.  The  vapour  of  this  alcohol,  when  passed  through  a  red-hot  glass- 
tube,  yields  a  mixture  of  gases,  among  which  a  carbo-hydrogen  CeHe  pre- 
dominates, which  has  the  chemical  character  of  defiant  gas,  and  to  which 
the  name  ■propijlene  has  been  given.  The  separation  of  this  gaseous  mixture 
has  hitherto  failed,  but  on  bringing  the  gas  in  contact  with  chlorine  a 
compound  CgHeCa  is  formed.  This  is  a  heavy  liquid  boiling  at  21 7° -4 
(103°C).  It  is  in  every  respect  analogous  to  the  Dutch-liquid  (see  page 
363),  originating  nuder  similar  circumstances  from  defiant  gas. 


POTATO-OIL    AND     ITS    DERIVATIVES.  389 

VMYL-ETHER,  AylO.  If  amyl-alcohol  is  distilled  with  concentrated  sul- 
\  cr'ic  acid,  a  mixture  of  several  substances  is  obtained,  which  has  to  be 
8v^  irated  by  distillation.  After  several  rectifications  an  oil  is  obtained, 
wh.ch  has  a  sp.  gr.  0-779  and  boils  at  348°-8  (170°C).  This  is  amyl-ether. 
The  composition  is  C,olli,0,  or,  if  we  adopt  the  double  formulas,  C20H22O2. 
Intermediate  ethers  between  amyl-  and  ethyl-,  and  likewise  between  amyl- 
and  methyl-ether  have  been  prepared.  They  contain  respectively  C14H16O2 
=:C4H50,C,oH,iO  and  C,2H,402  =  C2H30,C,oH,iO. 

CuLOBiDE  OF  AMYL,  Ayl  CI. — The  chloride  is  procured  by  subjecting  to 
distillation  equal  weights  of  potato-oil  and  pentachloride  of  phosphorus, 
washing  the  product  repeatedly  with  alkaline  water,  and  rectifying  it  from 
chloride  of  calcium.  Less  pure  it  may  be  obtained  by  saturating  fusel-oil 
with  hydrochloric  acid.  It  is  a  colourless  liquid,  of  agreeable  aromatic 
odour,  insoluble  in  water,  and  neutral  to  test-paper;  it  boils  at  215° 
(101°-7C),  and  ignites  readily,  burning  with  a  flame  green  at  the  edges.  By 
the  long-continued  action  of  chlorine,  aided  by  powerful  sunshine,  a  new 
product,  or  chlorinetted  chloride  of  amyl,  was  obtained  in  the  form  of  a  vola- 
tile colourless  liquid,  smelling  like  camphor,  and  containing  CioH^P^ ;  the 
whole  of  the  hydrogen  oould  not,  however,  be  removed. 

Bbomide  of  amyl,  Ayl  Br,  is  a  volatile,  colourless  liquid,  heavier  than 
water.  It  is  obtained  by  distilling  fusel-oil,  bromine  and  phosphorus 
together.  (See  bromide  of  ethyl,  page  353.)  Its  odour  is  penetrating  and 
alliaceous.  The  bromide  is  decomposed  by  an  alcoholic  solution  of  potassa 
with  production  of  bromide  of  the  metal. 

Iodide  of  Amyl,  Ayl  I,  is  procured  by  distilling  a  mixture  of  15  parts  of 
potato-oil,  8  of  iodine,  and  1  of  phosphorus.  It  is  colourless  when  pure, 
heavier  than  water,  volatile  without  decomposition  at  294° -8  {146°Cj  and 
resembles  in  other  respects  the  bromide ;  it  is  partly  decomposed  by  expo- 
sure to  light.  Iodide  of  amyl,  when  heated  in  sealed  tubes  with  zinc  to 
374°  (190°C)  yields  aniT/l,  a  colourless  liquid  of  an  ethereal  odour  contain- 
ing CjqH,,,  and  boiling  at  311°  (155°C).  Together  with  this  substance 
there  is  formed  iodide  of  zinc  and  zinc-amyl  C,oIIj,Zu,  which,  when  coming 
in  contact  with  water,  is  decomposed  into  oxide  of  zinc  and  hydride  of  amyl 
C,qH,2=:Ci(,H,iH,  which  is  an  exceedingly  volatile  substance,  boiling  at  86° 
(3U°C). 

Cyanide  of  amyl,  Ayl  Cy. — Colourless  liquid  of  0-800  sp.  gr.,  and  boiling 
at  294°-8  (14G°C),  which  i.s  obtained  by  distilling  cyanide  of  potassium  with 
sulphamylate  of  potassa.  Boiled  with  potassa,  this  compound  acid  under- 
goes a  decomposition  analogous  to  that  of  cyanide  of  ethyl  and  methyl,  (see 
pages  354  and  383;)  it  absorbs  4  eq.  of  water,  and  furnishes  ammonia  and 
the  potassa-salt  of  caproic  acid  C12H12O4,  one  of  the  constituents  of  butter, 
C,2H„N+4HO=C,2H,204+NH3. 

Acetate  of  oxide  of  amyl,  Ayl  OjCJIgOg. — This  interesting  product  is 
easily  obtained  by  submitting  to  distillation  a  mixture  of  1  part  of  potato-oil, 
2  parts  of  acetate  of  potassa,  and  1  part  of  concentrated  sulphuric  acid ;  it  is 
purified  by  washing  with  dilute  alkali,  and  distillation  from  chloride  of  cal- 
cium. It  presents  the  appearance  of  a  colourless,  limpid  liquid,  which  is  in- 
soluble in  water,  soluble  in  alcohol,  boils  at  272°  (133° -30,  and  becomes 
converted  by  an  alcoholic  solution  of  potassa  into  an  acetate  of  that  base, 
with  reproduction  of  fusel-oil.  This  ether  possesses  in  a  remarkable  manner 
the  odour  of  the  Jargonelle-pear.  It  is  now  manufactured  upon  a  largo 
scale  for  flavouring  liquors  and  confectionary. 

Carbonate  of  oxide  op  amyl,  Ayl  0,C02- — This  ether  has  been  lately 

obtained  by  Mr.  Medlock  by  saturating  fusel-oil  with  phosgene-gas  (chloro- 

carbonic  acid).     A  compound  analogous  to  chloro-carbonic  ether  AylO,C2C103 

is  first  produced,  which,  when  treated  with  water,  yields  hydrochloric  and  car- 

33* 


o90  POTATO-OIL    AND    ITS    DERIVATIVES. 

bonic  acids,  together  with  carbonate  of  amyl  (AylOjCjClOa-f  II0=AylO, 
C02-\-llGl-j-C02)'  Carbonate  of  amyl  is  a  colourless  liquid  of  an  aromatic 
odour,  boiling  at  438° -8  (226oC).  Alcoholic  solution  of  potassa  converts 
this  ether  into  fusel-oil,  carbonate  of  potassa  being  furmed  at  the  same  time. 

Sulphide  of  amyl,  aviyl-mercaptan,  and  numerous  other  compounds  of  like 
nature,  have  been  described. 

SuLPHAMYLic  ACID. — When  equal  weights  of  potato-oil  and  strong  sul- 
phuric acid  are  mixed,  heat  is  evolved,  accompanied  by  blackening  and  par- 
tial decomposition.  The  mixture  diluted  with  water,  and  saturated  with 
carbonate  of  baryta,  affords  sulphate  of  that  base,  and  a  soluble  salt  cor- 
responding to  the  sulphovinate.  The  latter  may  be  obtained  in  a  crystalline 
state  by  gentle  evaporation,  and  purified  by  re-solution  and  the  use  of  ani- 
mal charcoal.  It  forms  small,  brilliant,  pearly  plates,  very  soluble  in  water 
and  alcohol,  containing  BaO,CjoHiiO,2S03-f-HO.  The  baryta  may  be  pre- 
cipitated from  the  salt  by  dilute  sulphuric  acid,  and  the  hydrated  sulpha- 
mylic  acid  concentrated  by  spontaneous  evaporation  to  a  syrupy,  or  even 
crystalline  state ;  it  has  an  acid  and  bitter  taste,  strongly  reddens  litmus- 
paper,  and  is  decomposed  by  ebullition  into  potato-oil  and  sulphuric  acid. 
The  potassa-salt  forms  groups  of  small  radiated  needles,  very  soluble  in 
water.  The  sulphamylates  of  lime  and  protoxide  of  lead  are  also  soluble 
and  crystallizable. 

Amylene. — By  the  distillation  of  potato-oil  with  anhydrous  phosphoric 
acid,  a  volatile,  colourless,  oily  liquid  is  procured,  quite  different  in  proper- 
ties from  the  original  substance.  It  is  lighter  than  water,  boils  at  102° -2 
(39°C),  and  contains  no  oxygen.  Its  composition  is  represented  by  the 
formula  CioH,q  ;  consequently  it  not  only  corresponds  to  the  defiant  gas  in 
the  alcohol-series,  but  is  isomeric  with  that  substance.  Like  defiant  gas  it 
combines  directly  with  chlorine  and  bromine,  giving  rise  to  compounds 
CjjjIIioCIa  and  Ci^IIj^Brg.  The  vapour,  however,  has  a  density  of  2-68,  which 
is  2^  times  that  of  defiant  gas,  every  measure  containing  5  measures  of 
hydrogen. 

Together  with  this  substance  several  other  hydrocarbons  are  formed, 
espQcially  the  one  to  which  the  name  paramylene  has  been  given.  It  con- 
tains CaoIIao.  and  boils  at  320°  (160°C). 

Valekianic  or  valeric  acid. — M.  Dumas  has  shown  that  when  a  mixture 
of  equal  parts  of  quicklime  and  hydrate  of  potassa  is  moistened  with  alcohol, 
and  the  whole  subjected  to  a  gentle  heat,  out  of  contact  of  air,  the  alcohol 
is  oxidized  to  acetic  acid,  with  evolution  of  pure  hydrogen  gas.  At  a  higher 
temperature  the  acetate  of  potassa  produced  is  in  turn  decomposed,  yielding 
carbonate  of  potassa  and  light  carbonetted  hydrogen.  Wood-spirit,  by 
similar  treatment,  yields  hydrogen  and  formate  of  potassa,  which,  as  the 
heat  increases,  becomes  converted  into  carbonate,  with  continued  disengage- 
ment of  hydrogen.  In  like  manner  potato-oil,  the  third  alcohol,  suffers  under 
similar  circumstances,  conversion  into  a  new  acid,  bearing  to  it  the  same 
relation  that  acetic  acid  does  to  common  alcohol,  and  formic  acid  to  wood- 
spirit,  hydrogen  being  at  the  same  time  evolved.  The  body  thus  produce  J 
is  found  to  be  identical  with  a  volatile  oily  acid  distilled  from  the  root  Vale- 
riana officinalis. 

In  preparing  artificial  valerianic  acid,  the  potato-oil  is  heated  in  a  flask 
with  about  ten  times  its  weight  of  the  above-mentioned  alkaline  mixture 
during  the  space  of  10  or  12  hours ;  the  heat  is  applied  by  a  bath  of  oil 
or  fusible-metal  raised  to  the  temperature  of  390°  (198o-8C)  or  400° 
(204° -40).  When  cold,  the  nearly  white  solid  residue  is  mixed  with  water, 
an  excess  of  sulphuric  or  phosphoric  acid  added,  and  the  whole  subjected  to 
distillation.  The  distilled  liquid  is  supersaturated  with  potassa,  evaporated 
nealy  to  dryness  to  dissipate  any  undecomposed  potato-oil,  and  then  mixed 


POTATO-OIL    AND    ITS    DERIVATIVES.  391 

■with  Roracwhat  diluted  sulphuric  acid  in  excess.  The  greater  part  of  the 
valeTianic  acid  then  separates  as  an  oily  liquid,  lighter  than  water ;  this  is  a 
terhydrate  of  the  acid,  containing  three  equivalents  of  water,  one  of  which 
is  basic.  When  this  hydrate  is  distilled  alone,  it  undergoes  decomposition ; 
water,  with  a  little  of  the  acid,  first  appears,  and  eventually  the  pure  acid, 
in  the  form  of  a  thin,  fluid,  colourless  oil,  of  the  persistent  and  characteristic 
odour  of  valerian-root.  It  has  a  sharp  and  acid  taste,  reddens  litmus 
strongly,  bleaches  the  tongue,  and  bums  when  inflamed  with  a  bright,  yet 
smoky  light.  Valerianic  acid  has  a  density  of  0-937 ;  it  boils  at  370°  (175°C). 
Placed  in  contact  with  water,  it  absorbs  a  certain  quantity,  and  is  itself  to  a 
certain  extent  soluble.  The  salts  of  this  acid  present  but  little  interest,  as 
few  among  them  seem  to  be  susceptible  of  crystallizing.  The  liquid  acid  is 
found  by  analysis  to  contain  CjoHgOg.HO,  and  the  silver-salt,  AgOjCi^^HgOg. 
The  ether-compound  of  valerianic  acid  has  been  already  mentioned  (page 
357).  By  treatment  with  ammonia  this  ether  is  converted  into  valeramide 
CioHjiN02=Ci(,H902,NH2,  (analogous  to  acetamide,)  which,  under  the  influ- 
ence of  anhydrous  phosphoric  acid  loses  2  more  eq.  of  water,  becoming  vale- 
ronitrile  C,QHgN=CgHg,C2N  or  cyanide  of  butyl.  The  former  is  a  fusible 
crystalline  substance,  the  latter  a  volatile  liquid,  having  a  boiling  point  of 
257°  (125°C).  It  was  first  obtained  by  the  action  of_oxydizing  agents  upon 
gelatin.     (See  Section  VIII  on  the  components  of  the  animal  body.) 

A  more  advantageous  mode  of  preparing  valerianic  acid  is  the  following : 
— 4  parts  of  bichromate  of  potassa  in  powder,  6  parts  of  oil  of  vitriol,  and  8 
parts  of  water  are  mixed  in  a  capacious  retort;  1  part  of  pure  potato-oil  is 
then  added  by  small  portions,  with  strong  agitation,  the  retort  being  plunged 
into  cold  water  to  moderate  the  violence  of  the  reaction.  When  the  change 
appears  complete,  the  deep  green  liquid  is  distilled  nearly  to  dryness,  the 
product  mixed  with  excess  of  caustic  potassa,  and  the  aqueous  solution  sepa- 
rated mechanically  from  a  pungent,  colourless,  oily  liquid,  which  floats  upon 
it,  and  which  is  valerianate  of  amyl.  The  alkaline  solution  is  then  evaporated 
to  a  small  bulk  and  decomposed  by  sulphuric  acid  as  already  directed. 

Valerianic  acid  is  found  in  angelica  root,  in  the  bark  of  Viburnum  opulus, 
and  probably  exists  in  many  other  plants  ;  it  is  generated  by  the  spontaneous 
decomposition  of  azotized  substances,  mineral  and  vegetable,  and  is  produced 
in  many  chemical  reactions  in  which  oxidizing  agents  are  employed. 

If  an  open  jar  be  set  in  a  plate  containing  a  little  water,  and  having  beneath 
it  a  capsule  with  heated  platinum-black,  upon  which  potato-oil  is  slowly 
dropped  in  such  quantity  as  to  be  absorbed  by  the  powder,  the  sides  of  the 
jar  become  speedily  moistened  with  an  acid  liquid,  which  collects  in  the 
plate,  and  may  be  easily  examined.  This  liquid,  saturated  with  baryta-water, 
evaporated  to  dryness,  and  the  product  distilled  with  solution  of  phosphoric 
acid,  yields  valerianic  acid.' 

Some  very  beautiful,  and  for  the  progress  of  organic  chemistry,  highly 
important  results,  have  lately  been  obtained  by  the  action  of  electricity  upon 
valerianic  acid.  By  submitting  a  solution  of  valerianate  of  potassa  to  a  gal- 
.  vanic  current,  produced  by  4  elements  of  Bunsen's  battery.  Dr.  Kolbe  ob- 
served that  potassa  and  pure  hydrogen  were  evolved  at  the  negative  pole, 
while  at  the  positive  pole  valerianic  and  carbonic  acids,  an  odorous  inflam- 
mable gas,  and  an  ethereal  liquid,  made  their  appearance.  The  inflammable 
gas  obtained  in  this  reaction  is  a  carbohydrogen  CgHg  which  had  been  pre- 

*  Anhydrous  valerianic  acid  is  formed  by  the  reaction  between  valerianate  of  potassa  and 
oxychloriJe  of  phosphorus, 

5(K0,  C10II9O3)  and  PCl30a=2KOP05,  and  3KC1,  and  5(CioIIj07). 
It  is  an  oleaginous  liquid  lighter  than  water.    Boiling  water  rrbanpes  it  flowly  into  th« 
hydrateil  arid,  while  this  transformation  is  rapidly  affected  by  solutions  of  the  alkalies.     It 
boils  at  41'/^  (215^'C),  and  distils  unchanged.— 11.  U. 


892  POTATO-OIL    AND    ITS    DERIVATIVES. 

viously  isolated  by  Mr.  Faraday  from  the  oily  products  separated  from  com- 
pressed oil  gas.  This  substance,  to  which  the  name  butylene  has  been  given, 
is  perfectly  analogous  to  the  olefiant  gas  (ethylene),  propylene  and  amylene 
■which  have  been  previously  described.  It  combines  with  chlorine  and  bro- 
mine, forming  substances  analogous  to  Dutch  liquid.  The  oily  liquid  formed 
together  with  amylene,  in  the  electrolysis  of  valerianic  acid,  is  a  mixture  of 
several  substances,  among  which  a  hydrocarbon,  of  the  remarkable  compo- 
sition CgHg,  predominates.  This  body,  to  which  the  name  butyl  or  valyl  has 
been  given,  is  a  colourless  liquid,  of  an  agreeable  ethereal  odour,  and  boils 
at  226°-4  (108°C).  Kolbe  believes  that  this  hydrocarbon  must  be  viewed 
as  a  compound  analogous  to  methyl,  ethyl,  and  amyl,  with  which  we  have 
become  acquainted,  and  that  it  forms  the  radical  of  an  alcohol  yet  to  be  dis- 
covered, having  the  formula  CgHgO,  HO  and  analogous  to  methyl-,  ethyl-,  and 
amyl-alcohols,  an  alcohol  which,  by  oxidation,  would  yield  the  acid  CgH^Og, 
HO,  i.  e.,  butyric  acid,  just  as  the  three  alcohols  mentioned  are  converted 
respectively  into  formic,  acetic,  and  valeric  acids.  Kolbe  considers  butyl  to 
be  one  of  the  proximate  constituents  of  valeric  acid,  which  he  views  as  an 
intimate  combination  of  butyl  with  oxalic  acid,  butyl-oxalic  acid  CjoHgOgjHO 
:=CgHg,C203HO.  According  to  this  view,  the  transformation  of  valeric  acid 
under  the  influence  of  the  galvanic  current  is  readily  explained.  The  oxy- 
gen evolved  at  the  positive  pole  by  the  electrolysis  of  water  oxidizes  the  oxa- 
lic to  carbonic  acid,  and  liberates  the  butyl,  portions  of  which  are  farther 
attacked  by  the  oxygen,  and  deprived  of  1  eq.  of  hydrogen,  thus  giving  rise 
to  the  simultaneous  evolution  of  butylene.  If  this  view  holds  good  for  butyric 
acid,  it  must  be  equally  true  of  propionic,  acetic,  and  formic  acid,  and  of  a 
great  number  of  analogous  acids,  which  will  be  described  in  the  subsequent 
chapters  of  this  Manual. 

Propionic  acid  will  be  ethyl-oxalic  acid,  acetic  acid  methyl-oxalic,  and 
lastly,  formic  acid  hydrogen- oxalic  acid,  thus — 

Formic  acid...'. Cj  HO3,  H0=     H  ,C203,HO 

Acetic  acid , C4  H303,HO=C2H3,C203,HO 

Propionic  acid Cg  H503,HO=C4H5,C203,HO 

Valeric  acid CioH903,HO=C8Hg,C203,HO' 

This  view  is  borne  out  by  the  electrolytic  decomposition  of  acetic  acid,  which 
yields  a  gas,  considered  by  Kolbe  to  be  methyl.  Several  collateral  facts  have 
furnished  additional  support  to  this  theory,  amongst  which  may  be  quoted 
the  remarkable  deportment  of  the  ammonia-salts  of  these  acids  under  the 
influence  of  anhydrous  phosphoric  acid.     In  this  reaction,  oxalic,  formic, 

*  Butyric  acid  constitutes  the  fifth  member  of  this  series  as  a  combiaation  of  propyl  with 
oxalic  acid  or  propyl-oxalic  acid. 

Butyric  acid C8H903,HO=C6H7,C303,HO 

As  valyl  is  formed  from  valeric  acid,  so  the  decomposition  of  butyric  acid  should  yield  propyl 
Call'',  the  oxide  of  which  CbIItO  has  b^en  detected  in  cod-liver  oil  in  combination  with  oleic 
and  margaric  acid. 

Butylic  alcohol  of  Wurtz  appears  to  fill  up  this  vacancy  in  the  alcohol  series.  It  was 
extracted  from  rectified  potato-oil  by  fractional  distillations,  retaining  that  which  passes 
between  2260-4  (103°)  and  2440-4  (118°).  By  subsequent  purification  a  liquid  is  obtained  which 
boils  at  2330-6  (112°),  is  lighter  than  water,  has  the  odour  of  amylic  alcohol,  but  less  disagree- 
able. Fused  potassa  changes  it  into  butyric  acid  with  the  liberation  of  hydrogen.  Its  com- 
position is  Ceirio02=C8H90,HO,  or  hydrate  of  oxide  of  valyl. 

Butylic  alcohol,  when  mixed  with  its  own  weight  of  strong  sulphuric  acid  and  after  twenty- 
four  hours'  repose  saturated  with  carbonate  of  potassa,  yields  sulphate  and  sulphobutylate 
of  potassa.  The  latter  dis.folves  readily  in  boiling  absolute  alcohol,  from  which  it  is  deposited 
in  anhydrous  pearly  crystals  of  the  composition  K0,C8ll9O.2S0s. 

The  cyaiiate  and  cyanurate  of  butylic  ether  yield  with  potassa  a  nitrogenous  product, 
Imtylamin,  NllaCBlTg,  in  the  same  way  as  the  cyanates  and  cyanurates  of  ethyl,  methyl,  or 
amyl,  yiel.t  vospectively  rthylamin,  NII2C4II6,  methylamin  NHsCaHs,  and  amylamin  NHa 
CioHu.— K.  B. 


FUSEL-OIL    OF    GRAIN-SPIRIT.  393 

acetic,  propionic,  and  valeric  acids  yield  respectively  cyanogen  and  the  cya- 
nides of  hydrogen,  methyl,  ethyl,  and  butyl. 

NH4O,  C2O3— 4H0=  CgN 

NH4O,     II,  C2O3— 4H0=     H,  CjN 

NH40,C2H3,C203— 4HO  =  C2H3,C2N 

NH40,C4H5,C2O3— 4H0=C4H.,C2N 

NH40,C8H9,C203— 4HO=C8H9,C2N 

We  have  seen,  moreover,  that  the  cyanides  of  methyl  and  ethyl,  when  treated 
with  the  alkalis  are  readily  reconverted  into  acetic  and  propionic  acid,  and 
in  the  Section  on  cyanogen  it  will  be  shown  that  this  substance  and  hydro- 
cyanic acid  are  indeed  easily  convertible  into  oxalate  and  formate  of  ammonia. 
All  these  facts  are  readily  intelligible  by  the  view  proposed  by  Dr.  Kolbe. 

Chlorovalebisic  acid. — When  dry  chlorine  is  passed  for  a  long  time  into 
pure  valerianic  acid,  in  the  dark,  the  gas  is  absorbed  in  great  quantity,  and 
much  hydrochloric  acid  produced ;  towards  the  end  of  the  operation  a  littlo 
heat  becomes  necessary.  The  product  is  a  semi-fluid  transparent  substance, 
heavier  than  water,  odourless,  and  of  acrid  burning  taste.  It  does  not  congeal 
when  exposed  to  a  very  low  temperature,  but  acquires  complete  fluidity  when 
heated  to  86°  (30°C).  It  cannot  be  distilled  without  decomposition.  When 
put  into  water  it  forms  a  thin,  fluid  hydrate,  which  afterwards  dissolves  to  a 
considerable  extent.  This  body  is  freely  soluble  in  alkalis,  from  which  it  is 
again  precipitated  by  the  addition  of  an  acid.  Chlorovalerisic  acid  contains 
C,o(H6Cls)03,HO. 

Chloeovalerosic  acid.  —  This  is  the  ultimate  product  of  the  action  of 
chlorine  on  the  preceding  substance,  aided  by  exposure  to  the  sun.  It  re- 
sembles chlorovalerisic  acid  in  appearance  and  properties,  being  semi-fluid 
and  colourless,  destitute  of  odour,  of  powerful  pungent  taste,  and  heavier 
than  water.  It  can  neither  be  solidified  by  cold,  nor  distilled  without  decom- 
position. In  contact  with  water,  it  forms  a  hydrate  containing  3  eq.  of  that 
substance,  which  is  slightly  soluble.  In  alcohol  and  ether  it  dissolves  with 
facility.  It  forms  salts  with  bases,  of  which  the  best  defined  is  that  of  silver. 
Chlorovalerosic  acid  is  composed  of  Ci(,(H5Cl4)03,H0. 

Fusel-oil  of  grain-spirit.  —  The  fusel-oil  separated  in  large  quantities 
from  grain-spirit  by  the  London  rectifiers  consists  chiefly  of  potato-oil  (hy- 
drated  oxide  of  amyl)  mixed  with  alcohol  and  water.  Sometimes  it  contains 
in  addition  more  or  less  of  the  ethyl-  or  arayl-conipounds  of  certain  fatty 
acids  thought  to  have  been  identified  with  oenanthic  and  margaric  acids. 
These  last-named  substances  form  the  principal  part  of  the  nearly  solid  fat 
produced  in  this  manner  in  whisky-distilleries  conducted  on  the  old  plan. 
Mulder  has  described,  under  the  name  of  corn-oil,  another  constituent  of  the 
crude  fusel-oil  of  Holland ;  it  has  a  very  powerful  odour  resembling  that  of 
some  of  the  umbelliferous  plants,  and  is  unaflPected  by  solution  of  caustic 
potassa.  According  to  Mr.  Rowney,  the  fusel-oil  of  the  Scotch  distilleries 
contains  in  addition  a  certain  quantity  of  capric  acid  C20H20O4  which  is  one 
of  the  constituents  of  butter. 

The  fusel-oil  of  marc-brandy  of  the  south  of  France  was  found  by  M.  Balard 
to  contain  potato-oil  and  oenanthic  ether.  Potato-oil  has  been  separated  from 
the  spirit  distilled  from  beet-molasses,  and  from  artificial  grape-sugar  made 
by  the  aid  of  sulphuric  acid.  Although  much  obscurity  yet  hangs  over  the 
history  of  these  substances,  it  is  generally  supposed  that  they  are  products 
of  the  fermentation  of  sugar,  and  have  an  origin  contemDoraneous  with  that 
of  common  alcohol. 


It  is  impossible  to  leave  the  history  of  the  alcohols  without  alluding  to 
Bome  results  of  great  importance  for  the  elucidation  of  organic  compounds 


HOMOLOGOUS    SERIES. 

generally,  which  the  study  of  these  substances  has  elicited.  When  describing 
the  three  alcohols,  discussed  in  the  preceding  chapter,  we  have  repeatedly 
pointed  out  the  remarkable  analogy  presented  by  the  properties  and  the 
general  deportment  of  these  three  bodies.  If  we  compare  the  composition 
of  the  three  alcohols. 

Methyl-alcohol Cj  H^  Og 

Ethyl-alcohol C4  Hg  Og 

Amyl-alcohol CioHjaOg 

we  find  tfiat  their  formulae  present  an  unmistakable  symmetry.  All  three 
contain  the  same  amount  of  oxygen,  only  the  carbon  and  hydrogen  vary. 
This  variation,  however,  takes  place  in  very  simple  relations.  Thus  we  find 
the  diflFerence  of  ethyl-  and  methyl-alcohol  to  be  C4HgO,  —  CgH^Oj  =  CgHa, 
the  difi^erence  of  amyl-  and  methyl-alcohol  to  be  C10H12O2  — Ca^A  =  CgHg 
=4C2H2.  The  same  elementary  diff"erence  of  course  prevails  likewise  be- 
tween all  the  derivatives  of  the  three  alcohols. 

Iodide  of  methyl Cj  Hg  I 

Iodide  of  ethyl  C4  Hg  I  =  CJTgl -f    C^Ho 

Iodide  of  amyl  CioH^jI  =  CgHgl -f- 4C2H2 

or 

Formic  acid Cg  H  OgjHO 

Acetic  acid JO^  Hg  03,H0  =  C2H03,H0-f.   C2H2 

Valeric  acid CjoHg  Og.HO  =  C2HOg,HO  +  4C2H2 

Methylic,  ethylic,  and  amylic  alcohols  are  by  no  means  the  only  members 
of  this  class  which  are  known.  In  the  succeeding  sections  of  this  work  will 
be  noticed  a  series  of  compounds  evidently  of  a  perfectly  analogous  character 
which  have  been  discovered.  By  submitting  castor-oil  to  a  series  of  pro- 
cesses, M.  Bouis  has  formed  an  alcohol,  which  has  been  called  "caprylio 
alcohol."  According  to  M.  Dumas,  spermaceti  contains  another  analogous 
substance,  cetylic  alcohol,  which  is  a  solid  :  and  Mr.  Brodie  has  prepared 
two  alcohols,  cerotylic  and  mellisic,  from  ordinary  bees'  wax.  The  compo- 
sition of  these  substances  stands  in  exactly  the  same  relation  to  that  of  the 
preceding  alcohols,  which  we  have  pointed  out,  as  will  be  seen  from  the  fol- 
lowing table: — 

CapryUc  alcohol CigHigOa  =  CgH^Og  +    7C2H2 

Cetylic  alcohol C32H34O2  =  C2HA  -f  l^CaHg 

CerotyUc  alcohol C^HgA  =  C2H4O2  -f  26C2H2 

Melissic  alcohol  CeoHggOg  =  CgHA  -f  29C2H2 

These  four  alcohols,  when  submitted  to  the  action  of  oxidizing  agents,  are 
converted  into  four  acids,  analogous  to  formic  and  acetic  acid,  and  which 
stand  to  each  other,  and  to  formic  and  acetic  acid,  in  exactly  the  same  rela- 
tion as  the  various  alcohols. 

Caprylic  acid CjgHisOgJIO  =  CgHOgJIO  -}-    IC^II^ 

Cetylic  acid C32ll3,03,HO  =  C2H03,HO  -f  l^C^l^ 

Cerotylic  acid  CsJisgOgJIO  =  C2fI03,HO  -{-  2OC2H2 

Melissic  acid G^o^^^(\,UO  =  C2H03,HO  -f  29C2II2 

A  glance  at  these  tables  shows  that  all  the  alcohols  known  differ  from 
methyl-alcohols  by  C2H2,  or  a  multiple  of  it.  At  tlic  same  time,  it  is  evi- 
dent that  the  series  by  no  means  regularly  ascends.  Thus  we  perceive  tliat 
between  ethylic  and  amylic  alcohols  two  compounds  are  possible ;  in  like 
icanner  two  between  amylic  and  caprylic  alcohols. 

Even  now  the  parallel  series  of  volatib  acids  is  far  more  complete  than 


HOMOLOGOUS    SERIES. 


395 


that  of  the  alcohols.     At  present  the  following  members  of  this  group  arc 
known,  which  are  placed  in  juxtaposition  with  the  collateral  alcohols: — 


Methyl-alcohol Cg  H4  Oj 


Ethyl-alcohol  

....  C4  H,  O2 

(Tetryl-alcohol)..... 

....  Ce  H3  0, 

(Butyl-alcohol) 

....  C3  H,A 

Amyl-alcohol 

....  CjoHjaOg 

C12H14O2 

CuHteO^ 

Capryl-alcohol 

....       ClgHigOg 

C  18^20^2 

G20H22O2 

&c. 

&c. 

Formic  acid  Cj  H2O4 

Acetic  acid C4  H^  O4 

Propionic  acid Cg  Hg  O4 

Butyric  acid Cg  Hg  0^ 

Valeric  acid C,oH,q04 

Caproic  acid C12HJ2O4 

(Enanthylic  acid  CJ4HJ4O4 

Caprylic  acid  C,gH,g04 

Pelargonic  acid  Cj8H,804 

Capric  acid ^'2o^2(Pa 

&c.  &c. 

We  might  continue  the  scries  of  acids  uninterruptedly  to  C3gH3g04  (balenic 
acid),  and  with  intervals  even  much  higher  up  to  acids  containing  54  and 
even  more  equivalents  of  carbon.  Most  of  the  acids  belonging  to  this  series 
have  been  separated  from  fats,  and  hence  this  series  is  frequently  designated 
by  the  name  of  the  series  of  fatty  acids. 

A  series  of  analogous  substances  whose  composition  varies  by  C2H2,  or  a 
multiple  of  it,  is  called  a  series  of  homologous  bodies — a  name  first  used  by 
M.  Gerhardt,  to  whom  we  are  much  indebted  for  the  elucidation  of  this  sub- 
ject. It  is  evident  that  there  exist  as  many  such  homologous  series  as  there 
are  derivatives  of  any  one  of  the  alcohols.  We  may  construct  a  series  of 
homologous  radicals,  or  ethers,  or  hydrocarbons. 


Ethyl 

Propyl?.. 

Butyl 

Amyl 

Caproyl  .. 


.H3 
C4H5 
Cg  H7 


CjjHjj 


Methyl-ether..  Cg  H3  0 

Ether C4  H5  0 

(Tetryl-ether).  Cp  H^  O 


Amyl-ether . 


Ci^HjgO 


Ethylene C4  H4 

Propylene  ....  Cg  Hg 

Butylene Cg  Hg 

Amylene  C,oH,g 

Caproylene...  C,2H,2 


CigHi^O     Caprylene  ....  CjgHjg 


All  these  series  of  homologous  bodies  still  present  numerous  gaps ;  none 
perhaps  more  than  that  of  the  alcohols  which  may  be  taken  as  the  prototype 
of  all  the  rest ;  but  since  the  existence  of  these  homologous  series  was  first 
pointed  out,  many  gaps  have  been  filled,  and  it  may  be  expected  that  before 
long  the  rapid  strides  of  organic  chemistry  will  render  them  complete. 

The  properties  of  the  various  members  belonging  to  homologous  series 
gradually  change  as  we  ascend  in  the  series.  The  most  characteristic  alte- 
ration is  the  diminution  of  volatility,  A  regular  difference  between  the 
boiling  points  of  homologous  substances  was  first  pointed  out  by  H.  Kopp 
As  an  example  may  be  taken  the  series  of  fatty  acids : — 


Boiling  points. 


F, 

209° 
246° 
284° 
314°-6 

388°-4 


Formic  acid Cg  Hj  O4 

Acetic  acid C4  H4  O4 

Propionic  acid  Cg  Ilg  O4 

Butyric  acid Cg  Hg  O4 

Valeric  acid C,oH,o04 

Caproic  acid ^12^1204 

From  this  table  it  is  evident  that  the  boiling  temperature  of  the  homolo- 


c. 

98° 
119° 
140° 
157° 
175° 
198° 


Dififerences. 
F.  C. 


37° 

20°-5 

38° 

21° 

30° 

.7'' 

33°-4 

18° 

410.4 

23° 

f  ous  acids  rises  on  an  average 


(19° -90)  for  every  increment  of  Call^ 


A  similar  regular  difference  has  been  observed  in  the  boiling  points  of  manj 


396  BITTER- ALMOND     OIL 

homologous  compounds.     As  yet,  however,  the  number  of  cases  in  which 
discrepancies  occur  is  very  considerable. 

The  substances  discussed  in  the  next  three  sections  have  but  little  relation 
to  the  alcohols ;  they  may,  however,  be  here  most  conveniently  describea. 

BITTEU-ALMOND   OIL  AND   ITS   PRODUCTS. 

The  volatile  oil  of  bitter  almonds  possesses  a  very  high  degree  of  interest, 
from  its  study  having,  in  the  hands  of  MM.  Liebig  and  Wohler,  led  to  the 
first  discovery  of  a  compound  organic  body  capable  of  entering  into  direct 
combination  with  elementary  principles,  as  hydrogen,  chlorine,  and  oxygen, 
and  playing  in  some  degree  the  part  of  a  metal.  The  oil  is  supposed  to  be 
the  hybride  of  a  salt-basyle,  containing  €,411502,  called  benzoyl,  from  its  re- 
lation to  benzoic  acid,  which  radical  is  to  be  traced  throughout  the  whole 
series ;  it  has  been  isolated,  and  will  be  described  among  the  products  of 
distillation  of  the  benzoates. 

Table  of  Benzoyl- Compounds. 

Benzoyl,  symbol  Bz C!j4pT502 

Hydride  of  benzoyl;  bitter-almond  oil C14H5O2H 

Hydrated  oxide  of  benzoyl;  benzoic  acid C,4H5020,HO 

Chloride  of  benzoyl C,4H502C1 

Bromide  of  benzoyl C,4H502Br 

Iodide  of  benzoyl C14H5O2T 

Sulphide  of  benzoyl C14H5O2S. 

Hydride  of  benzoyl  ;  bitter-almond  oil  ;  BzH. — This  substance  is  pre- 
pared in  large  quantities,  principally  for  the  use  of  the  perfumer,  by  dis- 
tilling with  water  the  paste  of  bitter  almonds,  from  which  the  fixed  oil  has 
been  expressed.  It  certainly  does  not  pre-exist  in  the  almonds ;  the  fat  oil 
obtained  from  them  by  pressure  is  absolutely  free  from  every  trace  of  this 
principle  ;  it  is  formed  by  the  action  of  water  upon  a  peculiar  crystallizable 
substance,  hereafter  to  be  described,  called  amygdalin,  aided  in  a  very  ex- 
traordinary manner  by  the  presence  of  the  pulpy  albuminous  matter  of  the 
seed.  The  crude  oil  has  a  yellow  colour,  and  contains  a  very  considerable 
quantity  of  hydrocyanic  acid,  the  origin  of  which  is  contemporaneous  with 
that  of  the  oil  itself:  it  is  agitated  with  dilute  solution  of  protochloride  of 
iron  mixed  with  hydrate  of  lime  in  excess,  and  the  whole  subjected  to  dis- 
tillation; water  passes  over,  accompanied  by  the  purified  essential  oil,  which 
is  to  be  left  for  a  short  time  in  contact  with  a  few  fragments  of  fused  chlo- 
ride of  calcium  to  free  it  from  water. 

Pure  hydride  of  benzoyl  is  a  thin,  colourless  liquid,  of  great  refractive 
power,  and  peculiar  and  very  agreeable  odour;  its  density  is  1-043,  and  its 
boiling-point  356°  (180°C) :  it  is  soluble  in  about  30  parts  of  water,  and  is 
miscible  in  all  proportions  with  alcohol  and  ether.  Exposed  to  the  air,  it 
greedily  absorbs  oxygen,  and  becomes  converted  into  a  mass  of  crystallized 
benzoic  acid.  Heated  with  hydrate  of  potassa,  it  disengages  hydrogen,  and 
yields  benzoate  of  the  base.  The  vapour  of  the  oil  is  inflammable,  and  burns 
with  a  bright  flame  and  much  smoke.  It  is  very  doubtful  whether  pure 
bitter-almond  oil  is  poisonous;  the  crude  product,  sometimes  used  for  im- 
parting an  agreeable  flavour  to  puddings,  custards,  &c.,  and  even  publicly 
sold  for  that  purpose,  is  in  the  highest  degree  dangerous. 

Oxide  of  benzoyl  ;  benzoic  acid  ;  BzO. — This  is  the  sole  product  of  the 
oxidation  at  a  moderate  temperature  of  bitter-almond  oil ;  it  is  not,  how- 
ever, thus  obtained  for  the  purposes  of  experiment  and  of  pharmacy.  Seve- 
ral of  the  balsams  yield  benzoic  acid  in  great  abundance,  more  especially 
the  coucrete  resinous  variety  known  under  the  name  of  gum-benzoin.     When 


AND     ITS    PEODUCTS.  397 

vhis  substance  is  exposed  to  a  gentle  heat  in  a  subliming  vessel,  the  benzoic 
acid  is  volatilized,  and  may  be  condensed  by  a  suitable  arrangement.     The 
simplest  and  most  efficient  apparatus  for  this  and  all 
similar  operations  is  the   contrivance   of  Dr.  Mohr :  Fig.  171. 

it  consists  of  a  shallow  iron  pan,  (fig.  171,)  over  the 
bottom  of  which  the  substance  to  be  sublimed  is  thinly 
spread ;  a  sheet  of  bibulous-paper,  pierced  with  a 
number  of  pin-holes,  is  then  stretched  over  the  vessel, 
and  a  cap  made  of  thick,  strong  drawing  or  cartridge- 
paper,  secured  by  a  string  or  hoop  over  the  whole. 
The  pan  is  pl.aced  upon  a  sand-bath  and  slowly  heated 
to  tlie  requisite  temperature ;  the  vapour  of  the  acid 
condenses  in  the  cap,  and  the  crystals  are  kept  by  the 
thin  paper  diaphragm  from  falling  back  again  into  the 
pan.     Benzoic  acid  thus  obtained  assumes  the  form  of 

light,  feathery,  colourless  crystals,  which  exhale  a  fragrant  odour,  not 
belonging  to  the  acid  itself,  but  due  to  the  small  quantity  of  a  volatile  oil. 
A  more  productive  method  of  preparing  the  acid  is  to  mix  the  powdered  gum- 
benzoin  very  intimately  with  an  equal  weight  of  hydrate  of  lime,  to  boil 
this  mixture  with  water,  and  to  decompose  the  filtered  solution,  concentrated 
by  evaporation  to  a  small  bulk,  with  excess  of  hydrochloric  acid  ;  the  benzoic 
acid  crystallizes  out  on  cooling  in  thin  plates,  which  may  be  drained  upon  a 
cloth  filter,  pressed,  and  dried  in  the  air.  By  sublimation,  which  is  then 
efi"ected  with  trifling  loss,  the  acid  is  obtained  perfectly  white. 

Benzoic  acid  is  inodorous  when  cold,  but  acquires  a  faint  smell  when  gently 
warmed;  it  melts  just  below  212°  (100°C),  and  sublimes  at  a  temperature  a 
little  above;  it  boils  at  462°  (238° -SC),  and  emits  a  vapour  of  the  density 
of  4-27.  It  dissolves  in  about  200  parts  of  cold,  and  25  parts  of  boiling 
water,  and  with  great  facility  in  alcohol.  Benzoic  acid  is  not  aflFected  by 
ordinary  nitric  acid,  even  at  a  boiling  heat.  The  crystals  obtained  by  sub- 
limation, or  by  the  cooling  of  a  hot  aqueous  solution,  contain  an  equivalent 
of  water,  which  is  basic,  or  Cj^HgOgJIO. 

All  the  benzoates  have  a  greater  or  less  degree  of  solubility;  they  are 
easily  formed,  either  directly  or  by  double  decomposition.  Benzoates  of  the 
alkalis  and  of  ammonia  are  very  soluble,  and  somewhat  difficult  to  crystallize. 
Benzoate  of  lime  forms  groups  of  small  colourless  needles,  which  require  20 
parts  of  cold  water  for  solution.  The  salts  of  baryta  and  sirontia  are  soluble 
with  difficulty  in  the  cold.  Neutral  benzoate  of  the  sesqiiioxide  of  iron  is  a 
soluble  compound ;  but  the  basic  salt  obtained  by  neutralizing  as  nearly  as 
possible  by  ammonia  a  solution  of  sesquioxide  of  iron,  and  then  adding  ben- 
zoate of  ammonia,  is  quite  insoluble.  Sesquioxide  of  iron  is  sometimes  thus 
separated  from  other  metals  in  practical  analysis.  Neutral  and  basic 
benzoate  of  lead  are  freely  soluble  in  the  cold.  Benzoate  of  silver  crystallizes 
in  thin  transparent  plates,  which  blacken  on  exposure  to  light.  Some  re- 
markable products,  obtained  by  the  action  of  chlorine  upon  a  solution  of 
benzoate  of  potassa,  will  be  mentioned  in  the  section  on  the  Organic  Bases. 

NiTROBENzoic  ACID.  —  When  benzoic  acid  is  boiled  for  several  hours  with 
fuming  nitric  acid,  until  red  fumes  cease  to  appear,  it  yields  a  new  acid  body, 
in  which  the  elements  of  hyponitric  acid  are  substituted  for  an  equivalent  of 
hydrogen  of  the  original  benzoic  acid.  Nitro-benzoic  acid  greatly  resembles 
benzoic  acid  in  character,  and  contains  C,4H4N07,HO=C,4(H4N04)03,HO. 
The  remarkable  transformation  of  the  amide  of  this  acid,  of  niiro-benzamide, 
will  be  noticed  under  the  head  of  aniline. 

SuLPHOBENZOic  ACID.  — Benzoic  acid  is  soluble  without  change  in  conccn 
trated  oil  of  vitriol,  and  is  precipitated  by  the  addition  of  water ;  it  combineB. 
however,  with  anhydrous  sul^^huric  acid,  generating  a  compound  acid  aaalo* 
84 


398  BITTER-ALMOND    OIL 

gous  to  the  sulph«vinic,  but  bibasic,  forming  a  neutral  and  an  acid  series  of 
Baits.  The  baryta-compound  is  easily  prepared  by  dissolving  in  water  the 
viscid  mass  produced  by  the  union  of  the  two  bodies,  and  saturating  the 
solution  with  carbonate  of  baryta.  On  adding  hydrochloric  acid  to  the  filtered 
liquid,  and  allowing  the  whole  to  cool,  acid  sulphobenzoate  of  baryta  crys- 
tallizes out.  This  salt  has  an  acid  reaction,  and  requires  20  parts  of  cold 
water  for  solution  ;  the  neutral  salt  is  much  more  soluble.  The  hydrated 
acid  is  easily  obtained  by  decomposing  the  sulphobenzoate  of  baryta  by  dilut-*. 
sulphuric  acid ;  it  forms  a  white,  crystalline,  deliquescent  mass,  very  stabU 
and  permanent,  which  contains  Ci4H503,2SOs,2HO. 

Benzone,  benzophbnonb. — When  dry  benzoate  of  lime  is  distilled  at  a  high 
temperature,  it  yields  a  thick,  oily,  colourless  liquid,  of  peculiar  odour.  This 
is  a  mixture  of  several  compounds,  from  which,  however,  a  crystalline  sub- 
stance C13H5O,  or  CjeHigOg,  may  be  isolated,  to  which  the  name  benzone  or 
benzophenone  has  been  given.  Carbonate  of  lime  remains  in  the  retort ;  the 
reaction  is  thus  perfectly  analogous  to  that  by  which  acetone  is  produced  by 
the  distillation  of  a  dry  acetate. 

CaO,Ci4H503=Ci3H60-f-CaO,COa. 

The  benzophenone  is,  however,  always  accompanied  by  secondary  pi*oducts, 
due  to  the  irregular  and  excessive  temperature,  solid  hydrocarbons,  carbonic 
oxide,  and  benzol,  a  body  next  to  be  described. 

Benzol,  or  Benzine.  —  If  crystallized  benzoic  acid  be  mixed  with  three 
times  its  weight  of  hydrate  of  lime,  and  the  whole  distilled  at  a  temperature 
slowly  raised  to  redness  in  a  coated  glass  or  earthen  retort,  water,  and  a 
volatile  oily  liquid  termed  benzol,  pass  over,  while  carbonate  of  lime,  mixed 
with  excess  of  hydrate  of  lime,  remains  in  the  retort.  The  benzol  separated 
from  the  water,  and  rectified,  forms  a  thin,  limpid,  colourless  liquid,  of  strong 
agreeable  odour,  insoluble  in  water,  but  miscible  with  alcohol,  having  a  den- 
sity of  0-885,  and  boiling  at  176<^  (80<jC)  ;  the  sp.  gr.  of  its  vapour  is  2-738. 
Cooled  to  32°  (0°C),  it  solidifies  to  a  white,  crystalline  mass.  Benzol  contains 
carbon  and  hydrogen  only,  in  the  proportion  of  2  eq.  of  the  former  to  1  of 
the  latter,  or  probably  C,2H6-  It  is  produced  by  the  resolution  of  the  benzoic 
acid  into  benzol  and  carbonic  acid,  the  water  taking  part  in  the  reaction. 

Cun604=Ci2He-f2C02. 

Benzol  is  identical  with  the  bicarbide  of  hydrogen,  many  years  ago  dis- 
covered by  Mr.  Faraday  in  the  curious  liquid  condensed  during  the  compres- 
sion of  oil-gas,  of  which  it  forms  the  great  bulk,  being  associated  with  an 
excessively  volatile  hydrocarbon,  containing  carbon  and  hydrogen  in  the 
ratio  of  the  equivalents,  the  vapour  of  which  required  for  condensation  a 
temperature  of  0°  ( — 17°-7C).  This  is  the  substance  which  has  been  de- 
scribed under  the  name  of  butylene,  when  treating  of  valeric  acid  (see  page 
892). 

A  copious  source  of  benzol  has  been  lately  shown  by  Mr.  Mansfield  to  exist 
in  the  lightest  and  most  volatile  portions  of  coal-tar  oil,  which  will  be  noticed 
in  its  place  under  the  head  of  that  substance. 

SxiLPHOBENZiDE  AND  HYPOSULPHOBENZic  ACID.  — Bcuzol  Combines  directly 
with  anhydrous  sulphuric  acid,  to  a  thick  viscid  liquid,  soluble  in  a  small 
quantity  of  water,  but  decomposed  by  a  larger  portion,  with  separation  of  a 
crystalline  matter,  the  sulphobenzide,  which  may  be  washed  with  water,  in 
which  it  is  nearly  insoluble,  dissolved  in  ether,  and  left  to  crystallize  by 
spontaneous  evaporation.  It  is  a  colourless,  transparent  substance,  of  great 
importance,  fusible  at  212°  (100°C),  bearing  distillation  without  change,  and 
resisting  the  action  of  acids  and  other  energetic  chemical  agents.  Sulpho- 
benzide contains  CiaHsSOj.     It  may  be  viewed  as  benzol  in  which  1  eq.  of 


AND    ITS    PRODUCTS.  399 

hydrogen  has  been  replaced  by  1  eq.  of  sulphurous  acid.  The  s^i<t  liquid 
from  which  the  preceding  substance  has  been  separated,  neutralized  by 
carbonate  of  baryta  and  liltered,  yields  hyposulphobenzate  of  baryta,  which  is 
a  soluble  salt,  but  crystallizes  in  an  imperfect  manner.  By  double  decompo- 
sition with  sulphate  of  copper,  a  compound  of  the  oxide  of  that  metal  is 
obtained,  which  forms  fine,  large,  regular  crystals.  The  hydrate  of  hyposul- 
phobenzic  acid  is  prepared  by  decomposing  the  copper-salt  with  sulphuretted 
hydrogen ;  a  sour  liquid  is  obtained,  which  furnishes,  by  evaporation,  a 
crystalline  residue,  containing  Cj2H5S03j+HO,S03.  The  salts  of  potassa, 
soda,  ammonia,  and  of  the  oxides  of  zinc,  iron,  and  silver,  crystallize  freely. 
This  compound  acid  can  be  prepared  by  dissolving  benzol  in  Nordhausen 
sulphuric  acid. 

NiTROBENZOL. — Ordinary  nitric  acid,  even  at  a  boiling  temperature,  has  no 
action  on  benzol ;  the  red  fuming  acid  attacks  it,  with  the  aid  of  heat,  with 
great  violence.  The  product,  on  dilution,  throws  down  a  heavy,  oily,  yel- 
lowish, and  intensely  sweet  liquid,  which  has  an  odour  resembling  that  of 
bitter-almond  oil.  Its  density  is  1-209;  it  boils  at  415°  (212o-8C),  and  dis- 
tils but  not  without  being  slightly  changed.  It  is  but  little  affected  by  acids, 
alkalis,  or  chlorine,  and  is  quite  insoluble  in  water.  Nitrobenzol  contains 
C12H5NO4,  and  may  be  viewed  as  benzol,  in  which  1  eq.  of  hydrogen  is  re- 
placed by  1  eq.  of  hyponitric  acid.  When  nitrobenzol  is  heated  with  an  al- 
coholic solution  of  caustic  potassa,  and  the  product  subjected  to  distillation, 
a  red  oily  liquid  passes  over ;  this  is  a  mixture  of  several  substances  from 
which,  on  cooling,  large  red  crystals  separate,  which  are  nearly  insoluble  in 
water,  but  dissolve  with  facility  in  ether  and  alcohol.  This  compound, 
which  is  called  azobenzol,  melts  at  149°  (65°),  and  boils  at  379°  (192°-2C) ; 
it  contains  C12H5N.  Together  with  the  azobenzol  an  oil  is  produced,  which, 
contains  C12H7N,  and  has,  like  ammonia,  the  power  of  combining  with  acids. 
It  has  received  the  name  of  aniline,  and  will  be  described  in  the  section  on 
organic  bases.  The  reaction  which  gives  rise  to  azobenzol  and  aniline  in 
this  case,  is  not  yet  perfectly  understood,  several  other  substances  being  si- 
multaneously produced,  and  a  large  quantity  of  nitrobenzol  being  charred. 
Nitrobenzol  may,  however,  be  entirely  converted  into  aniline,  by  a  most  ele- 
gant process,  discovered  by  Zinin,  namely,  by  the  action  of  sulphide  of  am- 
monium, which  will  be  noticed  when  treating  of  aniline. 

BiNiTROBENZOL. — If  bcnzol  is  dissolved  in  a  mixture  of  equal  volumes  of 
concentrated  nitric  and  sulphuric  acids,  and  the  liquid  be  boiled  for  some 
minutes,  it  solidifies  on  cooling  to  a  mass  of  crystals,  which  are  easily  fu- 
sible, insoluble  in  water,  and  readily  soluble  in  alcohol.  They  contain  CxgH 
N208=Ci2(H42N04),  and  may  be  viewed  as  benzol  in  which  2  eq.  of  hydrogen 
are  replaced  by  2  eq.  of  hyponitric  acid. 

Benzol  and  chlorine  combine  when  exposed  fo  the  rays  of  the  sun ;  th< 
product  is  a  solid,  crystalline,  fusible  substance,  insoluble  in  water,  contain- 
ing CjjHgClg,  called  chlorobenzol.  When  this  substance  is  distilled,  it  is  de 
composed  into  hydrochloric  acid,  and  a  volatile  liquid,  chlorobenzide,  composed 

of     C^HgCl,. 

In  its  chemical  relations,  benzol  exhibits  the  character  of  a  substance  anal- 
ogous to  hydride  of  methyl  (marsh-gas),  hydride  of  ethyl,  and  hydride  af 
amyl. 

Benzol C,2Tl5H.=Hydriae  of  Pheuyl. 

Sulphobenzol CigHjSOj. 

Nitrobenzol CiaHgNO^. 

The  alcohol  belonging  to  this  hydride  is  known;  it  contains  CiaiTe'^a-- 

Cj^HjO^HO,  and  will  be  described  among  the  volatile  principles  of  coal-tar 

Chl'/kide  of  benzoyl,  BzCl. — This  compound  is  prepared  by  passing  drif 


400  BITTER -ALMOND    OIL 

chlorine  gas  through  pure  bitter-almond  oil,  as  long  as  hydrochloric  aciJ 
continues  to  be  formed ;  the  excess  of  chlorine  is  then  expelled  by  heat. 
Chloride  of  benzoyl  is  a  colourless  liquid  of  peculiar,  (.lisagreeable,  and  pun- 
gent odour.  Its  density  is  1-106.  The  vapour  is  inflammable,  and  burns 
with  a  tint  of  green.  It  is  decomposed  slowly  by  cold,  and  quickly  by  boil- 
ing water,  into  benzoic  and  hydrochloric  acids ;  with  an  alkaline  hydrate, 
benzoate  of  the  base,  and  chloride  of  the  metal,  are  generated. 

Benzamide. — When  pure  chloride  of  benzoyl  and  dry  ammoniacal  gas  are 
presented  to  each  other,  the  ammonia  is  energetically  absorbed,  and  a  white, 
solid  substance  produced,  which  is  a  mixture  of  sal-ammoniac  and  a  highly 
interesting  body,  benzamide.  The  sal-ammoniac  is  removed  by  washing  with 
cold  water,  and  the  benzamide  dissolved  in  boiling  water,  and  left  to  crys- 
tallize. It  forms  colourless,  transparent,  prismatic,  or  platy  crystals,  fusible 
at  239°  (115°C),  and  volatile  at  a  higher  temperature.  It  is  but  slightly 
soluble  in  cold,  freely  in  boiling  water,  also  in  alcohol  and  ether.  Benza- 
mide corresponds  to  oxamide,  both  in  composition  and  properties ;  it  con- 
tains Ci4H7N02=Ci4H502,NH2,  or  benzoate  of  oxide  of  ammonium,  minus  2 
eq.  of  water,  and  it  suffers  decomposition  by  both  acids  and  alkaline  solu- 
tions, yielding,  in  the  first  case,  a  salt  of  ammonia  and  benzoic  acid,  and,  in 
the  second,  free  ammonia  and  a  benzoate.  When  distilled  it  loses  again  2 
eq.  of  water,  and  becomes  benzonitrile.     (See  farther  on.) 

Iodide  of  Benzoyl,  BzI.  —  This  is  prepared  by  distilling  the  chloride  of 
benzoyl  with  iodide  of  potassium ;  it  forms  a  colourless,  crystalline,  fusible 
mass,  decomposed  by  water  and  alkalis,  in  the  same  manner  as  the  chloride. 
The  bronide  of  benzoyl,  BzBr,  has  very  similar  properties.  The  sulphide, 
BzS,  is  a  yellow  oil,  of  offensive  smell,  which  solidifies,  at  a  low  temperature, 
to  a  soft,  crystalline  mass.  Cyanide  of  benzoyl,  BzCy,  obtained  by  heating 
the  chloride  with  cyanide  of  mercury,  forms  a  colourless,  oily,  inflammable 
liquid,  of  pungent  odour,  somewhat  resembling  that  of  cinnamon.  All 
these  compounds  yield  benzamide  with  dry  ammonia. 

FoRMOBENZOio  ACID.  —  Crude  bitter-almond  oil  is  dissolved  in  water,  mixed 
with  hydrochloric  acid,  and  evaporated  to  dryness :  the  residue  is  boiled 
with  ether,  which  dissolves  out  the  new  substance,  and  leaves  sal-ammoniac. 
Formobenzoic  acid  forms  small,  indistinct,  white  crystals,  which  fuse,  and 
afterwards  suffer  decomposition  by  heat,  evolving  an  odour  resembling  that 
of  the  flowers  of  the  hawthorn,  and  leaving  a  bulky  residue  of  charcoal.  It 
is  freely  soluble  in  water,  alcohol,  and  ether,  has  a  strong  acid  taste  and  reac- 
tion, and  forms  a  series  of  crystallizable  salts  with  metallic  oxides.  This  sub- 
stance contains  CigH705,HO=Ci4Hg02-f-C2H03,HO,  or  the  elements  of  bitter- 
almond  oil,  and  formic  acid :  it  owes  its  origin  to  the  peculiar  action  of  strong 
mineral  acids  on  the  hydrocyanic  acid  of  the  crude  oil,  by  which  that  body 
suffers  resolution  into  formic  acid  and  ammonia.  It  is  decomposed  by  oxi- 
dizing bodies,  as  binoxide  of  manganese,  nitric  acid,  and  chlorine,  into  bitter- 
almond  oil  and  carbonic  acid. 

Hydrobenzamide.  —  Pure  bitter-almond  oil  is  digested  for  some  hours  at 
about  120°  (49°C)  with  a  large  quantity  of  strong  solution  of  ammonia  ;  the 
resulting  white  crystalline  product  is  washed  with  cold  ether,  and  dissolved 
in  alcohol ;  the  solution,  left  to  evaporate  spontaneously,  deposits  the  hydro- 
benzamide in  regular,  colourless  crystals,  which  have  neither  taste  nor  smell. 
This  substance  melts  at  a  little  above  212°  (100°C),  is  readily  decomposed 
by  heat,  dissolves  with  ease  in  alcohol,  but  is  insoluble  in  water ;  the  alco- 
holic solution  is  resolved  by  boiling  into  ammonia  and  bitter-almond  oil ;  a 
similar  change  happens  with  hydrochloric  acid.  Hydrobenzamide  contains 
C42H,aN2,  or  the  elements  of  3  equivalents  of  bitter-almond  oil,  and  2  of 
ammonia,  minus  0  equivalents  of  water.  When  impure  bitter-almond  oil  is 
employed  in  this  experiment,  the  products  are  different,  several  other  com- 


AND    ITS    PRODUCTS.  401 

pounds  being  obtained.  But  even  with  the  pure  oil  frequently  a  great  variety 
of  substances  are  formed.  The  hydrobenzamide  when  submitted  to  the  action 
of  chemical  processes  furnishes  a  great  number  of  derivatives,  of  which,  how- 
ever, only  one  substance,  namely,  amarine,  will  be  described  in  the  section 
on  the  organic  bases. 

Benzoin.  —  This  substance  is  found  in  the  residue  contained  in  the  retort 
from  which  bitter-almond  oil  has  been  distilled  with  lime  and  oxide  of  iron, 
to  free  it  from  hydrocyanic  acid ;  it  is  a  product  of  the  action  of  alkalis  and 
alkaline  earths  on  the  crude  oil,  and  is  said  to  be  only  generated  in  the 
presence  of  hydrocyanic  acid.  It  is  easily  extracted  from  the  pasty  mass,  by 
dissolving  out  the  lime  and  oxide  of  iron  by  hydrochloric  acid,  and  boiling 
the  residue  in  alcohol.  Benzoin  forms  colourless,  transparent,  brilliant, 
prismatic  crystals,  tasteless  and  inodorous ;  it  melts  at  248°  (120°C),  and 
distils  without  decomposition.  Water,  even  at  a  boiling  heat,  dissolves  but 
a  small  quantity  of  this  body ;  boiling  alcohol  takes  it  up  in  a  larger  propor- 
tion ;  it  dissolves  in  cold  oil  of  vitriol,  with  violet  colour.  Benzoin  contains 
0,4X1  jOg,  or  C28H12O4,  and  is,  consequently,  an  isomeric  modification  of  bitter- 
almond  oil. 

Benzile. — This  curious  compound  is  a  product  of  the  action  of  chlorine  on 
benzoin ;  the  gas  is  conducted  into  the  fused  benzoin  as  long  as  hydrochloric 
acid  continues  to  be  evolved.  It  is  likewise  formed  by  treating  benzoin  with 
fuming  nitric  acid.  The  crude  product  is  purified  by  solution  in  alcohol.  It 
forms  large,  transparent,  sulphur-yellow  crystals,  fusible  at  200°  (93°-3C), 
unaltered  by  distillation,  and  quite  insoluble  in  water.  It  dissolves  freely  in 
alcohol,  ether,  and  concentrated  sulphuric  acid,  from  which  it  is  precipitated 
by  water.  Benzile  is  composed  of  C14H5O2,  or  C28Hio04>  and  is  therefore  iso- 
meric with  the  radical  of  the  benzoyl-series. 

Benzolic  acid.  —  Benzoin  and  benzile  dissolve  with  the  violet  tint  in  an 
alcoholic  solution  of  caustic  potassa ;  by  long  boiling  the  liquid  becomes 
colourless,  and  is  then  found  to  contain  a  salt  of  a  peculiar  acid,  called  the 
benzilic,  which  is  easily  obtained  by  adding  hydrochloric  acid  to  the  filtered 
liquid,  and  leaving  the  whole  to  cool.  Benzilic  acid  forms  small,  colourless, 
transparent  crystals,  slightly  soluble  in  cold,  more  readily  in  boiling  water ; 
it  melts  at  248°  (120°C),  and  cannot  be  distilled  without  decomposition.  It 
dissolves  in  cold  concentrated  sulphuric  acid  with  a  fine  carmine-red  colour, 
Benzilic  acid  contains  CggHjjOg.HO,  or  2  eq.  benzile  and  1  eq.  water. 

Benzonitrile. — When  benzoate  of  ammonia  is  exposed  to  destructive  dis- 
tillation, among  other  products  a  yellowish  volatile  oil  makes  its  appearance, 
having  exactly  the  odour  of  bitter-almond  oil.  It  is  heavier  than  water, 
slightly  soluble  in  that  liquid,  boils  at  376°  (191°'1C),  and  contains  C14H5N. 
It  is  benzoate  of  ammonia, — 4eq.  of  water,  (NH40,C,4H503 — 4H0=Ci4H5N,) 
and  stands  to  this  salt  in  the  same  relation  as  cyanogen  to  oxalate,  hydro- 
cyanic acid  to  formate,  and  cyanide  of  methyl  to  acetate  of  ammonia.  Ben- 
zonitrile  likewise  may  be  viewed  as  a  cyanide,  when  it  becomes  a  member  of 
the  phenyl-series,  Ci4H5N=Ci2H5C2N. 

Benzoyl.  —  Benzoate  of  copper  by  dry  distillation  cautiously  conducted 
gives  a  residue  containing  salicylic  and  benzoic  acids,  and  an  oily  distilled 
product  which  crystallizes  on  cooling.  This  substance  possesses  the  odour 
of  the  geranium,  melts  at  158°  (70°C),  and  contains  C14H5O2.  It  was  dis- 
covered by  Ettling,  and  subsequently  studied  by  Stenhouse,  and  is  evidently 
the  radical  of  the  benzoyl-series.  I5y  heating  with  hydrate  of  potassa  it  is 
instantly  converted  into  benzoic  acid  with  disengagement  of  hydrogen. 

Benzimide.  —  This  is  a  white,  inodorous,  shining,  crystalline   substance 

occasionally  found  in  crude  bitter-almond  oil.     It  is  insoluble  in  water,  and 

but  slightly  dissolved  by  boiling  alcohol  and  ether.     Oil  of  vitriol  dissolves  it 

with  dark  indigo-blue  colour,  becoming  green  by  the  addition  of  a  little  water. 

34^ 


402        BITTER-ALMOND    OIL   AND    ITS    PROLUCTS. 

This  reaction  is  characteristic.  Benzimide  contains  C28lI,,N04.  It  may  be 
viewed  as  derived  from  an  acid  benzoate  of  ammonia  by  the  separation  of  4 
eq.  of  water. 

A  great  number  of  other  compounds  derived  from  bitter-almond  oil, 
directly  or  indirectly,  have  been  described  by  M.  Laurent  and  others.  Many 
of  these  contain  sulphur,  sulphuretted  hydrogen  and  sulphide  of  ammonium 
being  employed  in  their  preparation. 

HippuBic  ACID. — This  interesting  substance  is  in  some  measure  related  to 
the  benzoyl-compounds.  It  occurs,  often  in  large  quantity,  in  combination 
-with  potassa  or  soda,  in  the  urine  of  horses,  cows,  and  other  graminivorous 
animals.  It  is  prepared  by  evaporating  in  a  water-bath  perfectly  fresh 
cow-urine  to  about  a  tenth  of  its  volume,  filtering  from  the  deposit,  and 
then  mixing  the  liquid  with  excess  of  hydrochloric  acid.  Cow-urine  fre- 
quently deposits  hippuric  acid  without  concentration,  when  mixed  with  a 
considerable  quantity  of  hydrochloric  acid,  in  which  the  acid  is  less  soluble 
than  in  water.  The  brown  crystalline  mass  which  separates  on  cooling  is 
dissolved  in  boiling  water,  and  treated  with  a  stream  of  chlorine  gas  until 
the  liquid  assumes  a  light  amber  colour,  and  begins  to  exhale  the  odour  of 
that  substance  :  it  is  then  filtered,  and  left  to  cool.  The  still  impure  acid  is 
re-dissolved  in  water,  neutralized  with  carbonate  of  soda,  and  boiled  for  s, 
short  time  with  animal  charcoal ;  the  hot  filtered  solution  is,  lastly,  decom- 
posed by  hydrochloric  acid. 

Hippuric  acid  in  a  pure  state  crystallizes  in  long,  slender,  milk-white,  and 
exceedingly  frangible  square  prisms,  which  have  a  slight  bitter  taste,  fuse 
on  the  application  of  heat,  and  require  for  solution  about  400  parts  of  cold 
water ;  it  also  dissolves  in  hot  alcohol.  It  has  an  acid  reaction,  and  forma 
salts  with  bases,  many  of  which  are  crystallizable.  Exposed  to  a  high  tera- 
Derature,  hippuric  acid  undergoes  decomposition,  yielding  benzoic  acid,  ben- 
zoate of  ammonia,  and  a  fragrant  oily  matter,  with  a  coaly  residue.  With 
hot  oil  of  vitriol,  it  gives  off  benzoic  acid :  boiling  hydrochloric  acid  con- 
verts it  into  benzoic  acid  and  glycocine  (gelatin-sugar)  which  is  described  in 
the  Section  on  Animal  Chemistry.     Hippuric  acid  contains  CigHgN05,H0. 

The  constitution  of  hippuric  acid  has  been  frequently  discussed  by  che- 
mists. Very  different  views  have  been  proposed.  The  most  probable  one 
is,  that  it  is  the  amidogen  compound  of  a  peculiar  acid — glycobenzoic  acid. 
If  hippuric  acid  be  treated  with  nitrous  acid,  it  undergoes  the  decomposition 
peculiar  to  aTnidogen-compounds,  which  has  been  explained  when  treating  of 
oxamide  (page  343).  A  new  non-nitrogenous  acid  is  formed  together  with 
water  and  pure  nitrogen  Ci^HgNOgJIO-f  N03=C,8ll707,HO  +  HO+2N. 
Glycobenzoic  acid  is  a  crystalline  substance,  slightly  soluble  in  water,  but 
readily  dissolved  by  alcohol  and  ether.  It  may  be  viewed  as  a  conjugate 
acid,  containing  benzoic  and  glycolic  acids  —  2  eq.  of  water  CigHi^O^jHO 
=C,4H604,C4H406— 2H0.  Under  the  influence  of  boiling  water  it  splits 
indeed  into  benzoic  and  glycolic  acids.  Glycocine  must  be  considered  a- 
glycolamide  NH40,C4H305— 2HO  =  C4H5N04,  and  this  explains  the  conver- 
sion of  hippuric  acid  into  benzoic  acid  and  glycocine. 

If,  in  the  preparation  of  hippuric  acid,  the  urine  be  in  the  slightest  degree 
putrid,  the  hippuric  acid  is  all  destroyed  during  the  evaporation,  ammonia 
is  disengaged  in  large  quantity,  and  the  liquid  is  then  found  to  yield  nothing 
but  benzoic  acid,  not  a  trace  of  which  can  be  discovered  in  the  unaltered 
tjecretion.  Complete  putrefaction  effects  the  same  change  ;  benzoic  acid 
might  thus  be  procured  to  almost  any  extent. 

When  benzoic  acid  is  taken  internally,  it  is  rejected  from  the  system  in 
the  state  of  hippuric  acitl,  which  is  then  found  in  the  urine. 


BENZOYL-SERIES.  403 


HOMOLOGUES    OP   THE    BENZOYL-SEHIES. 

Toluylic  Acid,  Cigll^OgJIO-  —  This  substance,  -which  difibrs  from  benzoic 
acid  by  CgHg,  has  been  lately  discovered  by  Mr.  Noad,  who  obtained  it  by 
the  action  of  very  dilute  nitric  acid  upon  cymol,  a  carbo-hydrogen  occurring 
in  cumin-oil.  It  is  a  substance  exhibiting  the  closest  analogy  with  benzoic 
acid  both  in  its  physical  characters,  and  in  its  chemical  relations.  Like 
benzoic  acid,  when  treated  with  fuming  nitric  acid,  it  yields  a  nitro-acid, 
nitrotoluylic  acid,  Ci6H6N07,HO  =  C,^(H6N04)03,I10;  distilled  with  lime  or 
baryta,  it  furnishes  a  hydro-carbon  C,4Hg,  homologous  to  benzol.  The 
latter  substance,  which  has  received  the  name  of  toluol,  is  also  obtained 
from  other  sources,  especially  from  coal-tar  and  Tolu  balsam. 

An  acid  of  the  formula  CigHgOg.HO,  is  not  yet  known,  but  we  may  con- 
fidently expect  that  the  progress  of  science  will  not  fail  to  elicit  this  sub- 
stance ;  even  now  we  are  acquainted  with  a  hydrocarbon  C,gH,(,,  homologous 
to  benzol  and  toluol.  This  substance,  which  is  called  xylol,  is  found  in 
wood-tar  and  coal-gas-naptha,  and  stands  to  the  unknown  acid  CigllgOgHO 
in  the  same  relation  as  benzol  to  benzoic  acid.  Should  the  above  acid  be 
discovered,  we  may  with  certainty  predict  that,  when  distilled  with  excess 
of  lime,  it  will  yield  xylol. 

Cumic  acid,  C2oH,i03,HO. — Another  acid,  homologous  to  benzoic  acid, 
was  discovered  some  time  ago,  by  MM.  Cahours  and  Gerhardt.  It  is  formed 
by  the  oxydation  of  one  of  the  constituents  of  cumin-oil,  cuminol  CgoHjjOj, 
which  corresponds  to  oil  of  bitter  almonds.  It  likewise  yields  a  nitro-acid, 
nitro-cumic  acid  C2oH,qN07,HO  =  C2o(HjoN04)03,HO,  and  when  distilled  is 
converted  into  cumol  CigHij,  a  hydrocarbon,  homologous  to  benzol,  toluol, 
and  xylol. 

Of  the  next  series  only  the  hydrocarbon  is  known.  This  is  cymol  CgoH,^, 
the  substance  which,  as  has  been  mentioned  above,  is  the  source  of  toluylio 
acid. 

The  homology  of  these  substances  is  clearly  exhibited  by  the  following 
table : — 

Hydrides.  Acids.  Hydrocarbons 

derived  from  the  acid. 

Benzoyl-series C,4H502H  Ci4H503,HO  CijHe 

Toluyl-series CigH^Oa.HO  Ci4Hg 

Xylyl-series C,gH,o 

Cumyl-series CgoHuOgH  C2oHii03,HO  C,8H,2 

Cymyl-series C20H14 

This  table  shows  that  up  to  the  present  moment  only  the  series  of  hydro  • 
carbons  is  without  a  gap,  while  two  acids  and  three  hydrides  remain  to  bo 
discovered.  •* 


SALICTL   AND   ITS   COMPOUNDS. 

Salicin.  —  The  leaves  and  young  bark  of  the  poplar,  willow,  and  several 
other  trees  contain  a  peculiar  crystallizable,  bitter  principle,  called  salicin, 
which  in  some  respects  resembles  the  vegeto-alkalis  cinchonine  and  quinine, 
being  said  to  have  febrifuge  properties.  It  differs  essentially,  however,  from 
these  bodies  in  being  destitute  of  nitrogen,  and  in  not  forming  salts  with 
acids.  Salicin  may  be  prepared  by  exhausting  the  bark  with  boiling 
water,  concentrating  the  solution  to  a  small  bulk,  digesting  the  liquid  with 
I)owdere(l  protoxide  of  lead,  and  then,  after  freeing  the  fcolution  from  lead 
by  a  stream  of  sulphuretted-hydrogen  gas,  evaporating  until  the  salicin  crys- 


i04  S  AL  I  C  Y  L . 

tallizes  out  on  cooling.  It  is  purified  bj  treatment  with  animal  charcoal  and 
re-crystallization. 

Salicin  forms  small,  white,  silky  needles,  of  intensely  bitter  taste,  which 
have  no  alkaline  reaction.  It  melts  and  decomposes  by  heat,  burning  with 
a  bright  flame,  and  leaving  a  residue  of  charcoal.  It  is  soluble  in  5-6  parts 
of  cold  water,  and  in  a  much  smaller  quantity  when  boiling  hot.  Oil  of 
vitriol  colours  it  deep  red.  The  last  experiments  of  M.  Piria  give  for  sali- 
cin the  formula  C26H,gO,4. 

When  salicin  is  distilled  with  a  mixture  of  bichromate  of  potassa  and  sul- 
phuric acid,  it  yields,  among  other  products,  a  yellow,  sweet-scented  oil, 
which  is  found  to  be  identical  with  the  volatile  oil  distilled  from  the  flowers  of  the 
Spiroea  ulmaria,  or  common  meadow-sweet.  This  substance  appears  to  be  the 
hydride  of  a  compound  salt-radical,  salicyl,  containing  C14H5O4 ;  it  has  the 
properties  of  a  hydrogen-acid. 

Table  of  Salicyl- Compounds. 

Salicyl  (symb.  SI) •  C^Ji^        0< 

Hydrosalicylic  acid ^u^^i        ^J^ 

Salicylide  of  potassium ^,4115         O4K 

Hydrochlorosalicylic  acid C,4(H4C1)04H 

Hydriodosalicylic  acid Ci4{H4l)    O4H 

Hydrobromosalicylic  acid C,4(H4Br)04H 

Salicylic  acid C14H5       05,H0 

Hydrosalicylic  acid  ;  salicylous  acid  ;  artificial  oil  of  meadow- 
sweet, SIH. — One  part  of  salicin  is  dissolved  in  10  of  water,  and  mixed  in  a 
retort  with  1  part  of  powdered  bichromate  of  potassa  and  2^  parts  of  oil  of 
vitriol  diluted  with  10  parts  of  water;  gentle  heat  is  applied,  and  after  the 
cessation  of  the  effervescence  first  produced,  the  mixture  is  distilled.  The 
yellow  oily  product  is  separated  from  the  water,  and  purified  by  rectifica- 
tion from  chloride  of  calcium.  It  is  thin,  colourless,  and  transparent,  but 
acquires  a  red  tint  by  exposure  to  the  air.  Water  dissolves  a  sensible  quan- 
tity of  this  substance,  acquiring  the  fragrant  odour  of  the  oil,  and  the  cha- 
racteristic property  of  striking  a  deep  violet  colour  with  a  salt  of  sesquioxide 
of  iron,  a  property  however  which  is  also  enjoyed  by  salicylic  acid.  Alcohol 
and  ether  dissolve  it  in  all  proportions.  It  has  a  density  of  1-173,  and  boils 
at  385°  (166°-1C),  when  heated  alone.  Hydrosalicylic  acid  decomposes  the 
alkaline  carbonates  even  in  the  cold  ;  it  is  acted  upon  with  great  energy  by 
chlorine  and  bromine.  By  analysis  it  is  found  to  contain  Ci4Hg04,  or  the  same 
elements  as  crystallized  benzoic  acid ;  and  the  density  of  its  vapour  is  also 
the  same,  being  4-276. 

Salicylide  of  potassium,  KSl.  —  This  compound  is  easily  prepared  by 
mixing  the  oil  with  a  strong  solution  of  caustic  potassa ;  it  separates,  on  agi- 
tation, as  a  yellow  crystalline  mass,  which  may  be  pressed  between  folds  of 
blotting-paper,  and  re-crystallized  from  alcohol.  It  forms  large,  square, 
golden-yellow  tables,  which  have  a  greasy  feel,  and  .dissolve  very  easily  both 
in  water  and  alcohol ;  the  solution  has  an  alkaline  reaction.  When  quite 
dry,  the  crystals  are  permanent  in  the  air ;  but  in  a  humid  state  they  soon 
become  greenish,  and  eventually  change  to  a  black,  soot-like  substance,  in- 
soluble in  water,  but  dissolved  by  spirit  and  by  solution  of  alkali,  called 
mcla)iic  acid.  Acetate  of  potassa  is  formed  at  the  same  time.  Melanic  acid 
contains  C^U^O^q.  The  crystals  of  salicylide  of  potassium  contain  water 
Thich  cannot  be  expelled  without  partial  decomposition  of  the  salt. 

Salicylide  of  ammonium,  NH4SI,  crystallizes  in  yellow  needles  which  are 
quickly  desiroyed  with  production  of  ammonia  an«l  tlie  hydride.  Salicylide 
of  barium^  BaC,4H50  -j^-2H0,  forms  fine  yellow  acicular  crystals,  which  are 


s  A  L I  c  y  L .  405 

but  slightly  soluble  in  the  cold.     Salicylide  of  copper  is  a  green  insoluble 
powder,  containing  CUC14H5O4. 

Salicylide  of  copper  by  destructive  distillation  gives,  among  other  products, 
hydride  of  salicyl  and  a  solid  body  forming  colourless  prismatic  crystals, 
fusible  and  volatile.  It  is  insoluble  in  water,  dissolved  by  alcohol  and  ether, 
and  is  unaffected  by  fusion  with  hj'drate  of  potassa.  Nitric  acid  converts  it 
into  anilic  and  picric  acids.  (See  indigo).  It  contains  C14H5O3,  and  is  iso- 
meric with  anhydrous  benzoic  acid. 

Chlorohydro-salioylic  acid,  C,4(H4C1)04,H. — Chlorine  acts  very  strongly 
upon  the  hydride  of  salicyl ;  the  liquid  becomes  heated,  and  disengages  large 
quantities  of  hydrochloric  acid.  The  product  is  a  slightly  yellowish  crys- 
talline mass,  which,  when  dissolved  in  hot  alcohol,  yields  colourless  tabular 
crystals  of  the  pure  compound,  having  a  pearly  lustre.  This  substance  iai" 
insoluble  in  water  ;  it  dissolves  freely  in  alcohol,  ether,  and  solutions  of  the 
fixed  alkalis  ;  from  the  latter  it  is  precipitated  unaltered  by  the  addition  of 
an  acid.  It  is  not  even  decomposed  by  long  ebullition  with  a  concentrated 
solution  of  caustic  potassa.  Heated  in  a  retort,  it  melts  and  volatilizes,  con- 
densing in  the  cool  part  of  the  vessel  in  long,  snow-white  needles.  The 
odour  of  this  substance  is  peculiar  and  by  no  means  agreeable,  and  its  taste 
is  hot  and  pungent. 

Chlorohydro-salicylic  acid  combines  with  the  metallic  oxides ;  with  potassa 
it  forms  small  red  crystalline  scales,  very  soluble  in  water.  The  correspond- 
ing compound  of  barium,  prepared  from  the  foregoing,  by  double  decompo- 
sition, is  an  insoluble  crystalline,  yellow  powder,  containing  Ba  Cj4(H4Cl)0. 

Bromohydro-salicylic  acid,  Cj4(H4Br)04,H. — The  bromide-compound  ia 
prepared  by  the  direct  action  of  bromine  on  the  hydride  of  salicyl ;  it  crys- 
tallizes in  small  colourless  needles,  and  very  closely  resembles  in  properties 
the  chloride.  The  hydride  of  salicyl  dissolves  a  large  quantity  of  iodine,  • 
"  acquiring  thereby  a  brown  colour,  but  forming  no  combination ;  the  iodide 
may,  however,  be  procured  by  distilling  iodide  of  potassium  with  chlorohy- 
dro-salicylic acid.     It  sublimes  as  a  blackish-brown  fusible  mass. 

Chlorosamide. — The  action  of  dry  ammoniacal  gas  on  pure  chlorohydro- 
salicylic  acid  is  very  remarkable ;  the  gas  is  absorbed  in  large  quantity,  and 
a  solid  yellow,  resinous-looking  compound  produced,  which  dissolves  in 
boiling  ether,  and  separates  as  the  solution  cools  in  fine  yellow  iridescent 
crystals  ;  this  and  a  little  water  are  the  only  products,  not  a  trace  of  sal- 
ammoniac  can  be  detected.  Chlorosamide  is  nearly  insoluble  in  water ;  it 
dissolves  without  change  in  ether,  and  in  absolute  alcohol ;  with  hot  rectified 
spirit  it  is  partially  decomposed,  with  disengagement  of  ammonia.  Boiled 
with  an  acid,  it  yields  an  ammoniacal  salt  of  the  acid  and  chlorohydro-sali- 
cylic acid  ;  with  an  alkali,  on  the  other  hand,  it  gives  free  ammonia,  while 
chlorohydro-salicylic  acid  relnains  dissolved.  Chlorosamide  contains  G^ 
(H,5Cl3)N20g;  it  is  formed  by  the  addition  of  2  eq.  of  ammonia  to  3  eq.  of 
chlorohydro-salicylic  acid,  and  the  subsequent  separation  of  6  eq.  of  water 
A  corresponding  and  very  similar  substance,  bromosamide,  is  formed  by  the 
action  of  ammonia  on  bromohydro-salicylic  acid. 

Saligenin. — This  curious  substance  is  a  product  of  the  decomposition  of 
salicin  under  the  influence  of  the  emulsion  or  synaptase  of  sweet  almonds  ; 
it  is  also  generated  by  the  action  of  dilute  acids.  In  both  cases  the  salicin 
is  resolved  into  saligenin  and  grape  sugar.  Saligenin  forms  colourless,  na- 
creous scales,  freely  soluble  in  water,  alcohol,  and  ether.  It  melts  at  180*^ 
(82°C),  and  decomposes  at  a  higher  temperature.  Dilute  acids  at  a  boiling 
heat  convert  it  into  a  resinous-looking  substance,  Ci4Hg02,  called  saliretin. 
Many  oxidizing  agents,  as  chromic  acid  and  oxide  of  silver,  convert  this  sub- 
stance into  hydride  of  salicyl :  even  platinum-black  produces  this  effect.  Iti 
aqueous  solution  gives  a  deep  indigo-blue  colour  with  salts  of  sesquioxide  oi 


406  SALICYL. 

iron.     Saligenin  contams  C,4Hj,04.     Hence  the  transformation  of  salicin  is 
represented  by  the  equations : — 

2C26H,80h+8HO  =  C,J{,,0,,  =  2C,4H30^ 

Salitln.  Grape-sugar.     Saligenin. 

Salicin  yields  with  chlorine  substitution-compounds  containing  that  ele- 
ment, which  are  susceptible  of  decomposition  by  synaptase,  with  production 
of  bodies  termed  chloro-  and  hichlorosaligenin.  Chlorosaligenin  very  closely 
resembles  normal  saligenin,  and  contains  C,4(H7C1)04.  Certain  products, 
called  by  M.  Piria  helicin,  helicoidin,  and  anilotic  acid,  are  described  as  result- 
ing from  the  action  of  dilute  nitric  acid  upon  salicin.  With  strong  acid  at  a 
liigh  temperature  nitro-salicylic  add  (anilic  acid)  C|4(H4N04)05,HO,  is  pro- 
duced. 

Salicylic  acid,  S10,H0. — This  compound  is  obtained  by  heating  hydride 
of  salicyl  with  excess  of  solid  hydrate  of  potassa ;  the  mixture  is  at  first 
brown,  but  afterwards  becomes  colourless;  hydrogen  gas  is  disengaged 
during  the  reaction.  On  dissolving  the  melted  mass  in  water,  and  adding  a 
slight  excess  of  hydrochloric  acid,  the  salicylic  acid  separates  in  crystals, 
which  are  purified  by  re-solution  in  hot  water.  This  substance  very  much 
resembles  benzoic  acid ;  it  is  very  feebly  soluble  in  cold  water,  is  dissolved 
in  large  quantities  by  alcohol  and  ether,  and  maybe  sublimed  with  the  utmost 
ease.  It  is  charred  and  decomposed  by  hot  oil  of  vitriol,  and  attacked  with 
great  violence  by  strong,  heated  nitric  acid.  Salicylic  acid  contains  C14H5 
05,H0. 

Salicylic  acid  can  also  be  prepared  with  great  ease  by  fusing  salicin  with 
,  excess  of  hydrate  of  potassa,  and  also  by  the  action  of  a  concentrated  and 
hot  solution  of  potassa  upon  the  volatile  oil  of  Gaultheria  procumbens',  which 
is  the  methyl-compound  of  this  acid  occurring  in  nature  (see  essential  oils 
containing  oxygen).  When  salicylic  acid  is  mixed  with  powdered  glass  or 
Band  and  exposed  to  strong  and  sudden  heat  in  a  retort,  it  is  almost  entirely 
converted  into  carbonic  acid  and  hydrate  of  phenyl,  CijHgOj,  a  substance 
found  in  considerable  proportion  in  coal-tar-naphta, — and  the  same  change 
happens  to  many  of  its  salts  with  even  greater  facility. 

PiiLORiDziN. — This  is  a  substance  bearing  a  great  likeness  to  salicin,  found 
in  the  root-rind  of  the  apple  and  cherry-tree,  and  extracted  by  boiling  al- 
cohol. It  forms  fine,  colourless,  silky  needles,  soluble  in  1000  parts  of  cold 
water,  but  freely  dissolved  by  that  liquid  when  hot ;  it  is  also  soluble  with- 
out difficulty  in  alcohol.  It  contains  C42H24O20+4HO.  Dilute  acids  convert 
phloridzin  into  grape-sugar  and  a  crystallizable  sweet  substance  called  phlo- 
retin,  C2oH,40io. 

2(C42H2402o-f4HO)      =      C24H2,02g      -f      2C3oPThO,o 

Phloridzin.  Grape-sugar.  Phloretin. 

CuMARiN. — The  odoi'iferous  principle  of  the  tonka-bean.  It  may  be  often 
seen  forming  minute  colourless  crystals  under  the  skin  of  the  seed,  and  be- 
tween the  cotyledons.  It  is  best  extracted  by  macerating  the  sliced  beans 
in  hot  alcohol,  and,  after  straining  through  cloth,  distilling  olf  the  greater 
part  of  the  spirit.  The  syrupy  residue  deposits  on  standing  crystals  of  cu- 
marin,  which  must  be  purified  by  pressure  from  a  iat  oil  which  abounds  in 
the  beans,  and  then  crystallized  from  the  hot  water.  So  obtained,  cumarin 
forms  slender,  brilliant,  colourless  needles,  fusible  at  122°  (50°C),  and  dis- 
tilling without  decomposition  at  a  higher  temperature.  It  has  a  fragrant 
odour  and  burning  taste ;  it  is  very  slightly  soluble  in  cold  water,  moru 


CINNAMYL    AND    ITS    COMPOUNDS.  407 

freely  in  hot  water,  and  also  in  alcohol.  It  is  unaffected  by  dilute  acids  and 
alkalis,  which  merely  dissolve  it.  Boiling  nitric  acid  converts  it  into  picric 
acid,  and  a  hot  concentrated  solution  of  potassa  into  cumaric,  and  eventually 
into  salicylic  acid.  Cumarin  exists  in  several  other  plants,  as  the  Melilotm 
officinalis^  the  Asperula  adorata,  and  the  Anthozanthum  odoratum.  According 
to  M.  Bleibtreu  it  con     "       ~  ~  '  ~ 

CINNAMYL   AND   ITS    COMPOUNDS. 

The  essential  oil  of  cinnamon  seems  to  possess  a  constitution  analogous  to 
that  of  bitter-almond  oil;  it  passes  by  oxidation  into  a  volatile  acid,  the 
cinnamic,  which  resembles  in  the  closest  manner  benzoic  acid.  The  radical 
assumed  in  these  substajiccs  bears  the  name  of  cinnamyl ;  it  has  not  been 
isolated. 

Table  of  Cinnamyl- Compounds. 

Cinnamyl  (symbol  Ci)  CigH^Oj 

Chloride  of  cinnamyl  CigH^OjCI 

Hydride  of  cinnamyl ;  oil  of  cinnamon CjgH^OjH 

Hydrated  oxide  of  cinnamyl;  cinnamic  acid Cj8H7020,nO 

Cinnamylic  alcohol Cj8HgO,HO 

Cinnamate  of  cinnamylic  ether CigHgOjCigll^Og 

Hydride  of  cinnamyl  ;  oil  of  cinnamon  ;  CiH. — Cinnamon  of  excellent 
quality  is  crushed,  infused  twelve  hours  in  a  saturated  solution  of  common 
salt,  and  then  the  whole  subjected  to  rapid  distillation.  Water  passes  over, 
milky  from  essential  oil,  which  after  a  time  separates.  It  is  collected  and 
left  for  a  short  time  in  contact  with  chloride  of  calcium.  This  fragrant  and 
costly  substance  has,  like  most  of  the  volatile  oils,  a  certain  degree  of  solu- 
bility in  water ;  it  is  heavier  than  that  liquid,  and  sinks  to  the  bottom  of  the 
receiver  in  which  the  distilled  products  have  been  collected.  It  contains, 
according  to  M.  Dumas,  CjgHgOg. 

Cinnamic  acid,  CiO,HO.  —  When  pure  oil  of  cinnamon  is  exposed  to  the 
air,  or  inclosed  in  a  jar  of  oxygen,  it  is  quickly  converted  by  absorption  of 
gas  into  a  mass  of  white  crystalline  matter,  which  is  hydrated  cinnamic  acid ; 
this  is  the  only  product.  Cinnamic  acid  is  found  in  Peruvian  and  Tolu  bal- 
sams, associated  with  benzoic  acid,  and  certain  oily  and  resinous  substances ; 
it  may  be  procured  by  the  following  process  in  great  abundance,  and  in  a 
state  of  perfect  purity.  Old,  hard  Tolu  balsam  is  reduced  to  powder  and 
intimately  mixed  with  an  equal  weight  of  hydrate  of  lime ;  this  mixture  is 
boiled  for  some  time  in  a  large  quantity  of  water,  and  filtered  hot.  On  cool- 
ing, cinnamate  of  lime  crystallizes  out,  while  benzoate  of  lime  remains  in 
solution.  The  impure  salt  is  re-dissolved  in  boiling  water,  digested  with 
animal  charcoal,  and,  after  filtration,  suffered  to  crystallize.  The  crystals 
are  drained  and  pressed,  once  more  dissolved  in  hot  water,  and  an  excess  of 
hydrochloric  acid  being  added,  the  whole  is  allowed  to  cool ;  the  pure  cin- 
namic acid  separates  in  small  plates  or  needle-formed  crystals  of  perfect 
whiteness.  From  the  original  mother-liquor  much  benzoic  acid  can  be  pro- 
cured. 

The  crystals  of  cinnamic  acid  are  smaller  and  less  distinct  than  those  of 
benzoic  acid,  which  in  most  respects  it  very  closely  resembles.  It  melts  at 
248°  (120°C),  and  enters  into  ebullition  and  distils  without  change  at  560<» 
(293°-3C);  the  vapour  is  pungent  and  irritating.  Cinnamic  acid  is  much 
less  soluble,  both  in  hot  and  cold  water,  than  benzoic ;  a  hot  saturated  solu- 
tion becomes  on  cooling  a  soft-solid  mass  of  small  nacreous  crystals.  It 
dissolves  with  perfect  ease  in  alcohol.     Boiling  nitric  acid  iecomposeg  cin- 


408  CINNAMYL     AND    ITS     COMPOUNDS. 

namic  acid  with  great  energy,  and  with  production  of  copious  red  fumes ; 
bitter-almond-oil  distils  over,  and  benzoic  acid  remains  in  the  retort  in  which 
the  experiment  is  made.  When  cinnamic  acid  is  heated  in  a  retort  with  a 
mixture  of  strong  solution  of  bichromate  of  potassa  and  oil  of  vitriol,  it  is 
almost  instantly  converted  into  benzoic  acid,  which  afterwards  distils  over 
with  the  vapour  of  water:  the  odour  of  bitter-almond-oil  is  at  the  same 
time  very  perceptible.  The  action  of  chlorine  is  different ;  no  benzoic  acid 
is  formed,  but  other  products,  which  have  not  been  perfectly  studied. 

Cinnamic  acid  forms  with  bases  a  variety  of  salts  which  are  very  similar 
to  the  benzoatcs.  The  crystallized  acid  contains  CjgH^OgjHO.  When  dis- 
tilled with  an  excess  of  lime  or  baryta,  cinnamic  acid  undergoes  a  decompo- 
sition analogous  to  that  of  benzoic  acid;  an  oily  liquid  cinnamol  C,gHg  distils 
over,  whilst  a  carbonate  of  the  alkaline  earth  remains  behind,  CigHgO,,4- 
2BaO=2(BaO,C02)  +  C,8TIg.  This  oil  is  also  found  in  liquid  storax,  and  is 
frequently  described  by  the  term  styrol.    (See  resins  and  balsams.) 

Chlorocinnose. — This  is  the  ultimate  product  of  the  action  of  chlorine  on 
oil  of  cinnamon  by  the  aid  of  heat.  When  purified  by  crystallization  from 
alcohol,  it  forms  brilliant,  colourless  needles,  fusible,  and  susceptible  of  vola- 
tilization without  change.  It  is  not  affected  by  boiling  oil  of  vitriol,  and 
may  be  distilled  without  decomposition  in  a  current  of  ammoniacal  gas. 
Chlorocinnose  contains  C,8lT4Cl402 ;  it  is  formed  by  the  sul>stitution  in  the 
oil  of  cinnamon  of  4  eq.  of  chlorine  for  4  cq.  of  hydrogen.  The  true  chloride 
of  cinnamijl,  Ci  CI,  seems  to  be  first  formed  in  considerable  quantity,  and 
subsequently  decomposed  by  the  continued  action  of  the  chlonne ;  it  has  not 
been  separated  in  a  pure  state  ;  it  appears  as  a  very  thin,  fluid  oil,  convertible 
into  a  crystalline  mass  by  strong  solution  of  potassa. 

When  cinnamon-oil  is  treated  with  hot  nitric  acid,  it  undergoes  decompo- 
sition, being  converted  into  liydride  of  benzoyl  and  benzoic  acid.  With  a 
boiling  solution  of  chloride  of  lime  the  same  thing  happens,  a  bcnzoate  of  the 
base  being  generated.  If  the  oil  be  heated  with  solution  of  caustic  potassa 
it  remains  unaffected ;  with  the  solid  hydrate,  however,  it  disengages  pure 
liydrogen,  and  forms  a  potassa-salt,  which  appears  to  be  the  cinnamate. 
When  brought  into  contact  with  cold  concentrated  nitric  acid,  a  crystalline, 
yellowish,  scaly  compound  is  obtained,  which  is  decomposed  by  water  with 
separation  of  the  oil.  With  ammonia  a  solid  substance  is  produced,  which 
also  appears  to  be  a  direct  compound  of  the  two  bodies. 

Two  varieties  of  oil  of  cinnamon  are  met  with  in  commerce  of  very  unequal 
value,  viz.  that  of  China,  and  that  of  Ceylon ;  the  former  being  considered 
the  best :  both  are,  however,  evidently  impure.  The  pure  oil  may  be  ex- 
tracted from  them  by  an  addition  of  cold,  strong  nitric  acid ;  the  crystalline 
matter  which  forms  after  the  lai)se  of  a  few  hours,  separated  and  decomposed 
by  water,  yields    nre  hydride  of  cinnamyl. 


There  can  be  no  doubt  that  the  cinnamic  acid  in  Tolu  and  Peru  balsams 
is  gradually  formed  by  the  oxidation  of  a  substance  very  closely  related  to 
the  alcohols.  When  these  balsams  are  first  imported  they  are  nearly  fluid, 
but  gradually  acquire  consistence  by  keeping.  By  the  aid  of  an  alcoholic 
solution  of  potassa,  a  compound,  sometimes  oily,  sometimes  solid,  may  be 
separated  from  these  balsams,  which  cannot  be  distilled  without  partial  de- 
composition. This  compound,  described  respectively  under  the  name  of 
cinnamei7i  (when  oily),  and  styracin  (when  solid),  when  distilled  with  hydrate 
of  potassa,  is  converted  into  cinnamic  acid  and  a  neutral  substance,  which 
likewise  occurs  in  an  oily  and  crystalline  modification,  and  has  been  called, 
respectively,  peruvin  and  styronc.  These  substances  are  related  to  each  other 
vn  a  very  remarkable  manner.     Peruvin  may  be  viewed  as  the  alcohol  of 


CINNAMYL  AND  ITS  COMPOUNDS. 


409 


cinnamic  acid,  when  cinnamein  becomes  the  compound  ether  consisting  of 
alcohol  and  cinnamic  acid.  This  relation  will  become  obvious  by  the  fol- 
lowing formulae : — 


Ethyl-serieR. 

Alcohol C4H50,HO 

Acetic  acid  C4H303,H0 

Acetic  ether C4H50,C4H303 


Cinuamyl-series. 
Peruvin  C„HgO,HO 


Cinnamein CigHgOjCjgH^Oj 


When  treated  with  ox^^iizing  agents,  peruvin  yields  cinnamic  aftid,  or  its 
products  of  decomposition,  oil  of  bitter-almonds  and  benioic  acid. 


Sv*: 


410  VEGETABLE    ACID  6. 


SECTION  III. 
VEGETABLE   ACIDfl. 


The  vegetable  acids  constitute  a  very  natural  and  important  family  or 
group  of  compounds,  many  ot  which  possess  the  property  of  acidity,  i.  e. 
acid  reaction  to  litmus  paper,  and  power  of  forming  stable,  neutral,  and  often 
crystallizable  compounds  with  bases,  to  an  extent  comparable  with  that  of 
the  mineral  acids.  Some  of  these  bodies  are  very  widely  diffused  through 
the  vegetable  kingdom ;  others  are  of  much  more  limited  occurrence,  being 
found  in  some  few  particular  plants  only,  and  very  frequently  in  combina- 
tion with  organic  alkaline  bases,  in  conjunction  with  which  certain  of  them 
will  be  found  described.  Many  of  the  vegetable  acids  are  polybasic ;  and  it 
is  remarkable  that  in  the  new  products,  or  pyro-acids,  to  which  they  often 
give  rise  under  the  influence  of  heat,  this  character  is  usually  lost. 

The  particular  acids  now  to  be  described  are  for  the  most  part  of  extensive 
and  general  occurrence ;  mention  will  be  made  of  some  of  the  rarer  ones  ia 
connection  with  their  respective  sources. 

Table  of  Vegetable  Acids. 

Tartaric  acid Q^^0^Q,2TiK. 

Racemic  acid C8H40,o,2HO 

Citric  acid C,2H50,„3HO 

Aconitic,  or  equisetic  acid C4H  0^,110 

Malic  acid C8H408,2HO 

Fumaric  acid C4H  OgjHO 

Tannic  acid Ci8H509,3HO 

Gallic  acid C,H  03,2HO 

Taktaric  acid.  —  This  is  the  acid  of  grapes,  of  tamarinds,  of  the  pine- 
apple, and  of  several  other  fruits,  in  which  it  occurs  in  the  state  of  an  acid 
potassa-salt;  tartrate  of  lime  is  also  occasionally  met  with.  The  tartaric 
acid  of  commerce  is  wholly  prepared  from  the  tartar  or  argol,  an  impure  acid 
tartrate  of  potassa,  deposited  from  wine,  or  rather  grape-juice,  in  the  act  of 
fermentation.  This  substance  is  purified  by  solution  in  hot  water,  the  use 
of  a  little  pipe-clay,  and  animal  charcoal  to  remove  the  colouring-matter  of 
the  wine,  and  subsequent  crystallization;  it  then  constitutes  creavi  of  tartar  ^ 
and  serves  for  the  preparation  of  the  acid.  The  salt  is  dissolved  in  boiling 
water,  and  powdered  chalk  added  as  long  as  effervescence  is  excited,  or  the 
liquid  exhibits  an  acid  reaction;  tartrate  of  lime  and  neutral  tartrate  of 
potassa  result ;  the  latter  is  separated  from  the  former,  which  is  insoluble, 
by  filtration.  The  solution  of  tartrate  of  potassa  is  then  mixed  with  excess 
of  chloride  of  calcium,  which  throws  down  all  the  remaining  acid  in  the  form 
of  lime-salt;  this  is  washed,  added  to  the  former  portion,  and  then  the 
whole  digested  with  a  sufficient  quantity  of  dilute  sulphuric  acid  to  with- 
draw the  base  and  liberate  the  organic  acid.  The  filtered  solution  is  cau- 
tiously evaporated  to  a  syrupy  consistence  and  placed  to  crystallize  in  a  war'm 
situation. 


VEGETABLE     ACIDS.  411 

Tartaric  acid  forms  colourless,  transparent  crystals,  often  of  large  size, 
which  have  the  figure  of  an  oblique  rhombic  prism  more  or  less  modified ; 
these  are  permanent  in  the  air,  and  inodorous ;  they  dissolve  with  great 
facility  in  water,  both  hot  and  cold,  and  are  also  soluble  in  alcohol.  The 
solution  reddens  litmus  strongly,  and  has  a  pure  acid  taste.  The  aqueous 
solution,  as  has  been  mentioned  (page  76),  possesses  right-handed  polariza- 
tion. This  solution  is  gradually  spoiled  by  keeping.  Tartaric  acid  is 
bibasic;  the  crystals  contain  C^H40io,2HO.  This  substance  is  consumed  in 
large  quantities  by  the  calico-printer,  being  employed  to  evolve  chlorine  from 
somtion  of  bleach ing-powder  in  the  production  of  white  or  discharged  pat- 
terns upon  a  coloured  ground. 

Tartrate  of  potassa.  Neutral  tartrate  ;  soluble  tartar  ;  2K0, 
CgH^Oig. — The  neutral  salt  may  be  procured  by  neutralizing  cream  of  tartar 
with  chalk,  as  in  the  preparation  of  the  acid,  or  by  adding  carbonate  of 
potassa  to  cream  of  tartar  to  saturation :  it  is  very  soluble,  and  crystallizes 
with  difficulty  in  right  rhombic  prisms,  which  are  permanent  in  the  air,  and 
have  a  bitter,  saline  taste. 

Acid  tartrate  of  potassa;  cream  of  tartar;  KO,HO,CgIT40,o. —  The 
origin  and  mode  of  preparation  of  this  substance  have  been  already  de- 
scribed. It  forms  small  transparent  or  translucent  prismatic  crystals,  irre- 
gularly grouped  together,  which  grit  between  the  teeth.  It  dissolves  pretty 
freely  in  boiling  water,  but  the  greater  part  separates  as  the  solution  cools, 
leaving  about  -^^  or  less  dissolved  in  the  cold  liquid.  The  salt  has  an  acid 
reaction,  and  a  sour  taste.  When  exposed  to  heat  in  a  close  vessel,  it  is  de- 
composed with  evolution  of  inflammable  gas,  leaving  a  mixture  of  finely- 
divided  charcoal  and  pure  carbonate  of  potassa,  from  which  the  latter  may 
be  extracted  by  water.  Cream  of  tartar  is  almost  always  produced  when 
tartaric  acid  in  excess  is  added  to  a  moderately  strong  solution  of  a  potassa- 
salt,  and  the  whole  agitated. 

Tartratts  of  soda.  —  Two  compounds  of  tartaric  acid  with  soda  are 
known:  a  neutral  salt,  2NaO,CgH40,o-f-4HO ;  and  an  acid  salt,  NaO,HO, 
CgH40,(,-|-2IIO.  Both  are  easily  soluble  in  water,  and  crystallize.  Tartaric 
acid  and  bicarbonate  of  soda  form  the  ordinary  ejfervescing  draughts. 

Tartrate  of  potassa  and  soda  ;  Rochelle  or  seignette  salt  ;  KO, 
NaO,CgH4O,Q-j-10nO. — This  beautiful  salt  is  made  by  neutralizing  with  car- 
bonate of  soda  a  hot  solution  of  cream  of  tartar,  and  evaporating  to  the 
consistence  of  thin  syrup.  It  separates  in  large,  transparent,  prismatic 
crystals,  the  faces  of  which  are  unequally  developed  ;  these  effloresce  slightly 
in  the  air,  and  dissolve  in  1^  parts  of  cold  water.  Acids  precipitate  cream 
of  tartar  from  the  solution.  Rochelle  salt  has  a  mild,  saline  taste,  and  is 
used  as  a  purgative. 

Tartrates  of  ammonia.  — The  neutral  tartrate  is  a  soluble  and  efflorescent 
salt,  containing  2NH^O,C8H40,o-f2HO.  The  add  tartrate,  NH40,HO,C8H40,o, 
closely  resembles  ordinary  cream  of  tartar.  A  salt  corresponding  to  Rochelle 
salt  also  exists,  having  oxide  of  ammonia  in  place  of  soda. 

The  tartrates  of  lime,  baryta,  strontia,  magnesia,  and  of  the  oxides  of  most 
of  the  metals  proper,  are  insoluble,  or  nearly  so,  in  water. 

Tartrate  of  antimony  and  potassa  ;  tartar  emetic. — This  salt  is  easily 
made  by  boiling  teroxide  of  antimony  in  solution  of  cream  of  tartar ;  it  is 
deposited  from  a  hot  and  concentrated  solution  in  crystals  derived  from  an 
octahedron  with  rhombic  base,  which  dissolve  without  decomposition  in  15 
parts  of  cold,  and  3  of  boiling  water,  and  have  an  acrid  and  extremely  dis- 
agreeable taste.  The  solution  is  incompatible  with,  and  decomposed  by,  both 
acids  and  alkalis ;  the  former  throw  down  a  mixture  of  cream  of  tartar  and 
teroxide  of  antimony,  and  the  latter,  the  teroxide,  which  is  again  dissolved 
by  great  excess  of  the  reagent.     Sulphuretted  hydrogen  separates  all  the 


412  VEGETABLE    ACIDS. 

antimony  in^  the  state  of  tersulphide.  Heated  in  a  dry  state  on  charcoal 
before  the  blowpipe,  it  yields  a  globule  of  metallic  antimony.  The  ^s/ rstals 
contain  KO.SbOg.CgH^Oio-f  2H0.» 


An  analogous  compound  containing  arsenious  acid  (AsOg)  in  plact*  of  ter- 
oxide  of  antimony  has  been  described.  It-  has  the  same  crystalline  form  as 
tartar-emetic. 

A  solution  of  tartaric  acid  dissolves  hydrated  sesquioxide  of  iron  in  large 
quantity,  forming  a  brown  liquid  which  has  an  acid  reaction,  and  dries  up  by 
gentle  heat  to  a  brown,  transparent,  glassy  substance,  destitute  of  all  traces 
of  crystallization.  It  is  very  soluble  in  water,  and  the  solution  is  not  pre- 
cipitated by  alkalis,  fixed  or  volatile.  Indeed,  tartaric  acid  added  in  sufficient 
quantity  to  a  solution  of  sesquioxide  of  iron  or  alumina,  entirely  prevents 
the  precipitation  of  the  bases  by  excess  of  ammonia.  Tartrate  and  ammoni- 
acal  tartrate  of  iron  are  used  in  medicine,  these  compounds  having  a  less 
disagreeable  taste  than  most  of  the  iron-preparations. 

Solution  of  tartaric  acid  gives  white  precipitates  with  lime-  and  baryta- 
water,  and  with  acetate  of  lead,  which  dissolve  in  excess  of  the  acid ;  with 
neutral  salts  of  lime  and  baryta  no  change  is  produced.  The  effect  on  solu- 
tion of  potassa-salts  has  been  already  noticed. 


Action  of  heat  on  tartaric  acid.  —  When  crystallized  tartaric  acid  is 
exposed  to  a  temperature  of  400°  (204° -50)  or  thereabouts,  it  melts,  loses 
water,  and  passes  through  three  different  modifications,  called  in  succession 
tariralic,  tartrelic,  and  anhydrous  tartaric  acid.  The  two  first  are  soluble  in 
water,  and  form  salts,  which  have  properties  completely  different  from  those 
of  ordinary  tartaric  acid.  The  third  substance,  or  anhydrous  acid,  is  a  white 
insoluble  powder.  All  three,  in  contact  with  water,  slowly  pass  into  comipon 
tartaric  acid.    Their  composition  is  thus  expressed : — 

Ordinary  tartaric  acid CgH40,o,2HO 

Tartralic  acid 2C8H40io,3HO 

Tartrelic  acid C8H40io,HO 

Anhydrous  acid C8H4O1Q 

The  analogy  borne  by  these  bodies  to  the  several  modifications  of  phos- 
phoric acid  will  be  at  once  evident. 

Pyrotartaric  acid.  —  When  crystallized  tartaric  acid  is  subjected  to 
destructive  distillation,  a  heavy  acid  liquid  containing  this  substance  passes 
over,  accompanied  by  a  large  quantity  of  carbonic  acid ;  in  the  retort  is  left 
a  semi-fluid  black  mass,  which,  by  farther  heating,  gives  combustible  gases, 
an  empyreumatic  oil,  and  a  residue  of  charcoal.  The  distilled  product 
exhales  a  powerful  odour  of  acetic  acid,  and  is  with  great  difficulty  purified. 
Pyrotartaric  acid  forms  a  series  of  salts,  and  an  ether ;  it  is  supposed  to  con^ 
tain  CgHgOgjHO.  A  second  pyro-acid  sometimes  separates  in  crystals  from  the 
preceding  compound,  and  may  be  obtained  in  larger  quantity  by  the  destruc- 
tive distillation  of  cream  of  tartar ;  it  is  composed  of  0511303,110, 

When  tartaric  acid  is  heated  to  400°  (204° -50)  with  excess  of  hydrate  of 
potassa,  it  is  resolved  without  charring  or  secondary  decomposition  into  oxa- 

»  According  to  Dumas,  KO,Sb03,C8H40i(>4-HO.  Dried  at  212°  (lOOOC),  an  equiv.ilent  of 
water  is  lost,  and  at  428°  (220°C),  two  additional  equivalents,  leaving  the  compound  KO,SbOs, 
CeH^Os,  which  can  no  longer  contain  ordinary  tartaric  acid.  Nevertheless,  when  dissolved  in 
water^  the  crystals  again  take  up  the  elements  of  water  and  reproduce  the  original  salt. 


VEGETABLE     ACIDS.  413 

he  *ti(i  aceti'   *cids,  which  remain  in  union  with  the  base,  and  only  undergo 
decomposition  at  a  much  higher  temperature. 

Racemic  acid  ;  paratartario  acid.  —  The  grapes  cultivated  in  certain 
districts  of  the  Upper  Rhine,  and  also  in  the  Vosges,  in  France,  contain,  in 
association  with  tartaric  acid,  another  and  peculiar  acid  body,  to  which  the 
term  racemic  acid  is  given ;  it  is  rather  less  soluble  than  tartaric  acid,  and 
separates  first  from  the  solution  of  that  substance.  Between  these  two  acids, 
however,  the  greatest  possible  resemblance  exists ;  they  have  exactly  the 
same  composition,  and  yield,  when  exposed  to  heat,  the  same  products  ;  the 
ealts  of  racemic  acid  correspond,  in  the  closest  manner,  with  the  tartrates. 
A  solution  of  this  acid  precipitates  a  neutral  salt  of  lime,  which  is  not  the 
case  with  tartaric  acid.  A  solution  of  racemic  acid  does  not  rotate  the  plane 
of  polarization. 

Racemic  acid  has  been  lately  the  subject  of  some  exceedingly  interesting 
researches  by  M.  Pasteur,  which  have  thrown  much  light  upon  the  relation 
of  this  acid  to  tartaric  acid.  If  racemic  acid  be  saturated  with  potassa,  or 
soda,  or  with  most  other  bases,  crystals  are  obtained,  which  are  identical  in 
form  and  physical  properties.  By  satm-ating  racemic  acid,  however,  with 
two  bases,  by  forming,  for  instance,  compounds  corresponding  to  Rochelle- 
salt,  which  contain  potassa  and  soda  or  ammonia  and  soda,  and  allowing  the 
solution  to  crystallize  slowly,  two  varieties  of  crystals  arer  produced,  which 
may  be  distinguished  by  their  form,  namely,  as  the  image  and  the  reflection 
of  the  image,  or  as  right-handed  and  left-handed.  If  the  two  kinds  of 
crystals  are  carefully  selected  and  separately  crystallized,  "in  each  case  crys- 
tals of  the  one  variety  only  are  deposited.  The  composition,  the  specific 
gravity,  and,  in  fact,  most  of  the  physical  properties  of  these  two  varieties 
of  racemate  of  potassa  and  soda,  are  invariably  the  same.  They  diiFer,  how- 
ever, somewhat  in  their  chemical  characters,  and  especially  in  one  point, 
they  rotate  the  plane  of  polarization  in  opposite  directions.  (See  page  76.) 
M.  Pasteur  assumes  in  the  two  varieties  of  crystals  the  existence  of  twp 
modifications  of  the  same  acid,  which  he  distinguishes,  according  as  the  salts 
possess  right-  or  left-handed  polarization,  by  the  terms  deztroracemic  and 
levoracemic  acids.  These  acids  can  be  separated  by  converting  the  above 
compounds  into  lend-  br  baryta-salts,  and  decomposing  them  by  means  of 
sulphuric  acid.  In  this  manner  two  crystalline  acids  are  obtained,  identical 
in  every  respect  excepting  in  their  deportment  with  polarized  light,  and  in 
their  crystals  behaving  as  image  and  reflection.  It  is  very  probable,  not  to 
say  certain,  that  dextroracemic  acid  is  nothing  but  common  tartaric  acid. 
A  mixture  of  equal  parts  of  the  two  acids  has  no  longer  the  slightest  eftect 
on  polarized  light,  and  exhibits  in  every  respect  the  deportment  of  racemic 
acid. 

Citric  acid. — Citric  acid  is  obtained  in  large  quantity  from  the  juice  of 
limes  and  lemons  ;  it  is  found  in  many  other  frviits,  as  in  gooseb^mes,  cur- 
rants, &c.,  in  conjunction  with  another  acid,  the  malic.  In  the  preparation 
of  this  acid,  the  juice  is  allowed  to  fferment  a  short  time,  in  order  that  muci- 
lage and  other  impurities  may  separate  and  subside ;  the  clear  liquor  is  then 
carefully  saturated  with  chalk,  which  forms,  with  the  citric  acid,  an  insoluble 
compound.  This  is  thoroughly  washed,  decomposed  by  the  proper  quantity 
of  sulphuric  acid,  diluted  with  water,  and  the  filtered  solution  evaporated  to 
a  small  bulk,  and  left  to  crystallize.  The  product  is  drained  from  the.  mother- 
liqnor,  re-dissolved,  digested  with  animal  charcoal,  and  again  concentrated 
to  the  crystallizing-point.  Citric  acid  forms  colourless,  prismatic  crystals, 
wh;ch  have  a  pure  and  agreeable  acid  taste;  they  dissolve,  with  great  ease, 
in  '^oth  hot  and  cold  water ;  the  solution  strongly  reddens  litmus,  and,  when 
lorg  kept,  is  subject  to  spontaneous  change. 

Citric  acid  is  tribasic;  its  formula  in  the  gentW  dried  and  anhydrous  silver 
35* 


414       ^  VEGETABLE    ACIDS. 

Bait  is  C12H5O,,.  The  hydrated  acid  crystallizes  with  two  different  quantities 
of  water,  assuming  two  different  forms.  The  crystals,  which  separate  by 
spontaneous  evaporation  from  a  cold  saturated  solution,  contain  CjjHjOu, 
3HO-f-2HO,  the  last  being  water  of  crystallization ;  while,  on  the  other  hand, 
those  which  are  deposited  from  a  hot  solution  contain  but  4  equivalents  of 
water  altogether,  three  of  which  are  basic.  Citric  acid  is  entirely  decomposed 
when  heated  with  sulphuric  and  nitric  acids ;  the  latter  converts  it  into  oxalic 
acid.  Caustic  potassa,  at  a  high  temperature,  resolves  it  into  acetic  and 
oxalic  acids.*  When  subjected  to  the  action  of  chlorine,  the  alkaline  citrates 
yield  among  other  products  chloroform. 

The  citrates  are  very  numerous,  the  acid  forming,  like  ordinary  phosphoric 
acid,  three  classes  of  salts,  which  contain  respectively  3  eq.  of  a  metallic 
oxide,  2  eq.  of  oxide  and  1  eq.  of  basic  water,  and  1  eq.  oxide  and  2  eq.  basic 
water,  besides  true  basic  salts,  in  which  the  water  of  crystallization  is  perhaps 
replaced  by  a  metallic  oxide. 

The  citrates  of  the  alkalis  are  soluble  and  cry stalliz able  with  greater  or 
less  facility ;  those  of  baryta,  strontia,  lime,  lead,  and  silver  are  insoluble. 

Citric  acid  resembles  tartaric  acid  in  its  relations  to  sesquioxide  of  ii*on ; 
it  prevents  the  precipitation  of  that  substance  by  excess  of  ammonia.  The 
citrate,  obtained  by  dissolving  the  hydrated  sesquioxide  in  solution  of  citric 
acid,  dries  up  to  a  pale-brown,  transparent,  amorphous  mass,  which  is  not 
very  soluble  in  water ;  an  addition  of  ammonia  increases  the  solubility. 
Citrate  and  amiponio-citrate  of  iron  are  elegant  medicinal  preparations.  Very 
little  is  known  respecting  the  composition  of  these  curious  compounds ;  the 
absence  of  crystallization  is  a  great  bar  to  inquiry. 

Citric  acid  is  sometimes  adulterated  with  tartaric;  the  fraud  is  easily 
detected  by  dissolving  the  acid  in  a  little  cold  water,  and  adding  to  the  solu- 
tion a  small  quantity  of  acetate  of  potassa.  If  tartaric  acid  be  present,  a 
white  crystalline  precipitate  of  cream  of  tartar  will  be  produced  on  agitation. 

AcoNiTic,  OR  EQUisETic  ACID.  —  When  crystallized  citric  acid  is  heated  in 
a  retort  until  it  begins  to  become  coloured,  and  to  undergo  decomposition, 
and  the  fused,  glassy  product,  after  cooling,  dissolved  in  water,  an  acid  is 
obtained,  differing  completely  in  properties  from  citric  acid,  but  identical 
with  an  acid  extracted  from  the  Aconitum  napellus  and  the  Equisetum  fluviatile. 
Aconitic  acid  forms  a  white,  confusedlj^-crystalline  mass,  permanent  in  the 
air,  and  very  soluble  in  water,  alcohol,  and  ether  ;  the  solution  has  an  acid 
and  astringent  taste.  The  salts  of  aconitic  acid  possess  but  little  interest ; 
that  of  baryta  forms  an  insoluble  gelatinous  mass ;  aconilate  of  lime,  which 
has  a  certain  degree  of  solubility,  is  found  abundantly  in  the  expressed  juice 
of  the  monkshood,  and  aconitate  of  magnesia  in  that  of  the  equisetum. 

Hydrated  aconitic  acid  contains  C4H03,HO;  it  is  formed  in  the  artificial 
process  above  described,  by  the  breaking  up  of  1  eq.  of  hydrated  citric  acid, 
C,2HgOx4,  into  2  eq.  of  water  and  3  eq.  of  hydrated  aconitic  acid.  There 
are,  however,  invariably  many  secondary  products  formed,  such  as  acetone, 
carbonic  oxide,  and  carbonic  acid,  Tfee  farther  action  of  heat  upon  aconitic 
acid  gives  rise  to  several  new  acids,  especially  citraconic  and  ilaconic  acids, 
both  expressed  by  the  formula  CgHjOj.HO.  The  limits  of  this  elementary 
work  will  not  permit  us  to  enter  into  a  description  of  these  farther  products 
of  decomposition. 

Malic  acid. — This  is  the  acid  of  apples,  pears,  and  various  other  fruits ; 
it  is  often  associated,  as  already  observed,  with  citric  acid.     An  excellent 

*  The  easy  resolution  of  tartaric  and  citric  acids  into  a  mixture  of  oxalic  and  acetic  adds 
by  the  action  of  heat,  aided  by  the  presence  of  a  powerful  base,  has  led  to  the  idea  of  the  pos- 
sible pre-existence  of  those  last-named  bodies  in  the  two  vegetable  acids,  -w-hich  may  thus  be 
compounded  of  two  acids  of  simpler  constitution,  forming  coupled  or  conjugate  acids,  of  which 
several  have  been  supposed  to  exist.  These  views,  although  sometimes  useful,  pxe  not  at 
present  supported  by  ovidenco  of  great  impoi-tance. 


VEGETABLE    ACIDS.  415 

process  for  preparing  the  acid  in  question  is  that  of  Mr.  Everitt,  who  has 
demonstrated  its  existence,  in  great  quantity,  in  the  juice  of  the  common 
garden  rhubarb ;  it  is  accompanied  by  acid  oxalate  of  potassa.  The  rhubarb 
stalks  are  peeled,  and  ground  or  grated  to  pulp,  which  is  subjected  to  pres- 
sure. The  juice  is  heated  to  the  boiling-point,  neutralized  with  carbonate 
of  potassa,  and  mixed  with  acetate  of  lime  ;  insoluble  oxalate  of  lime  falls, 
which  is  removed  by  filtration.  To  the  clear  and  nearly  colourless  liquid, 
solution  of  acetate  of  lead  is  added  as  long  as  a  precipitate  continues  to  be 
produced.  The  malate  of  lead  is  collected  on  a  filter,  washed,  diffused 
through  water,  and  decomposed  by  sulphuretted  hydrogen.*  The  filtered 
liquid  is  carefully  evaporated  to  the  consistence  of  syrup,  and  left  in  a  dry 
atmosphere  until  it  becomes  converted  into  a  solid  and  somewhat  crystalline 
mass  of  malic  acid:  regular  crystals  have  not  been  obtained.  From  the 
berries  of  the  mountain-ash  (sorbus  aucuparia)  in  which  malic  acid  is  like- 
wise present  in  considerable  quantity,  especially  at  the  time  they  commence 
to  ripen,  the  acid  may  be  prepared  by  the  same  process. 

Malic  acid  is  bibasic,  its  formula  being  C8H40g,2HO ;  it  forms  a  variety 
of  salts,  some  of  which  are  neutral,  others  acid.  In  the  presence  of  fer- 
menting substances,  especially  of  putrifying  casein,  it  is  itself  decomposed, 
yielding  succinic,  acetic,  and  carbonic  acid. 

3(C8H408,2HO)  =  2(C8H406,2HO)  +  C4H303,HO-f  4C02+2HO. 

Malic  acid.  Succinic  acid.      Acetic  ^cid. 

Sometimes  also  butyric  acid  and  hydrogen  are  observed  among  the  products 
of  this  decomposition.  Malic  acid  is  colourless,  slightly  deliquescent,  and 
very  soluble  in  water ;  alcohol  also  dissolves  it.  The  aqueous  solution  has 
an  agreeable  acid  taste ;  it  becomes  mouldy,  and  spoils  by  keeping.  The 
most  characteristic  of  the  malates  are  the  acid  malate  of  ammonia,  NH40,H0, 
CgH408,  which  crystallizes  remarkably  well,  and  the  malate  of  lead,  which  is 
insoluble  in  pure  water,  but  dissolves,  to  a  considerable  extent,  in  warm 
dilute  acid,  and  separates,  on  cooling,  in  brilliant,  silvery  crystals  which  con- 
tain water.  The  acid  may,  by  this  feature,  be  distinguished.  The  acid  ma- 
late of  lime,  CaO,HO,CgH40g-f-6HO,  is  also  a  very  beautiful  salt,  freely  solu- 
ble in  warm  water.  It  is  prepared  by  dissolving  the  sparingly  soluble  neutral 
malate  of  lime  in  hot  dilute  nitric  acid,  and  leaving  the  solution  to  cool. 

Recent  researches  of  M.  Piria  have  established  a  most  intimate  relation 
between  malic  acid  and  two  substances — asparagin  and  aspartic  acid,  which 
will  be  described  in  one  of  the  succeeding  sections.  These  compounds  may 
be  viewed  as  malamide  and  malamic  acid,  analogous  to  oxamide  and  oxamic 
acid. 

Oxalic  acid '     .     .    0406,2HO  Malic  acid     .     .      C,H408,2HO 

Neutral  oxalate  of  |  c^Oe,2NH40        {  ^^^J^fj^^^^*';^}  C8H408,2NH40 


ammonia  ^  ^    ^. 

1  r-  TTTM  n  /  Malamide  ;  aspa- 1  n  tt  x:  r. 


Oxamide   .     .     .    }C4H4NA  { '^^17'.' '."'"}  ^s^sNA 


Binoxalate  of  am-  \  n  c\   rxn  xru  n    J  Bimalate   of  am- 
monia    .      .      .      |C406,HO,NH40    I    ^^^.^      _      _      ^     |v.8ra4V^8,xiu,i.xa4i^ 

Oxamicacid     .       }C4H,N0„H0      {^^.ttTJl^M  \'"]  ^^^^NO.HO 

'  If  the  acid  be  required  pure,  crystallized  malate  of  lead  must  be  used,  the  freshly  preci- 
pitated salt  invariably  carrying  down  a  quantity  of  lime,  which  cannot  be  removed  by  simple 
washing. 

'We  have  here  doubled  the  formula  of  oxalic  acid,  when  it  becomes  bibasic,  like  malic  aciil. 
There  are,  in  fact,  many  features  in  the  history  of  oxalic  acid,  which  render  it  probable  tha 
it  is  bibasic.    In  the  text  we  have  still  retained  the  generally  received  formula. 


416  VEGETABLE    ACIDS. 

Hitherto  neither  asparagin  nor  aspartic  acid  have  been  actually  obtained 
from  malic  acid.  On  the  contrary,  these  substances  are  converted  with  the 
greatest  facility  into  malic  acid.  On  passing  a  current  of  nitroxis  acid  into 
a  solution  of  asparagin  or  aspartic  acid,  pure  nitrogen  is  evolved,  malic  being 
liberated. 

C^HgNjOe  4-  2NO3  =  08H408,2irO  +  2110  +  4N 
Asparagin.  Malic  acid. 

FuMARic  AND  MALEic  ACIDS.  —  If  malic  acid  be  heated  in  a  small  retort, 
nearly  filled,  it  melts,  emits  water,  and  enters  into  ebullition ;  a  volatile 
acid  passes  over,  which  dissolves  in  the  water  of  the  receiver.  After  a  time, 
small  solid,  crystalline  scales  make  their  appearance  in  the  boiling  liquid, 
and  increase  in  quantity,  until  the  whole  becomes  solid.  The  process  may 
now  be  interrupted,  and  the  contents  of  the  retort,  after  cooling,  treated 
with  cold  water ;  unaltered  malic  acid  is  dissolved  out,  and  the  new  sub- 
stance, having  a  smaller  degree  of  solubility,  is  left  behind;  it  is  called 
fumaric  acid,  from  its  identity  with  an  acid  extracted  from  the  common 
fumitory. 

Fumaric  acid  forms  small,  white,  crystalline  laminse,  which  dissolve  freely 
in  hot  water  and  alcohol,  but  require  for  that  purpose  about  200  parts  of 
cold  water  ;  it  is  unchanged  by  hot  nitric  acid.  When  heated  in  a  current 
of  air  it  sublimes,  but 'in  a  retort  undergoes  decomposition.  This  is  a 
phenomenon  often  observed  in  organic  bodies  of  small  volatility.  Fumavic 
acid  forms  salts  which  have  been  examined  by  M,  Pdeckher,  and  an  ethor, 
which,  by  the  action  of  ammonia,  yields  a  white,  amorphous,  insoluble 
powder,  called  fumar amide,  corresponding  in  properties  and  constitution 
with  oxamide.  Hydrated  fumaric  acid  contains  C4H03,H0;  hence  it  is 
isomeric  with  aconitic  acid. 

The  volatile  acid  produced  simultaneously  with  the  fumaric  acid  is  called 
maleic  acid  ;  it  may  be  obtained  in  crystals  by  evaporation  in  a  warm  place. 
It  is  very  soluble  in  water,  alcohol,  and  ether;  it  has  a  strong  acid  taste 
and  reaction,  and  is  convertible  by  heat  into  fumaric  acid.  Hydrated  maleic 
acid  contains  CgH206,2HO.  Maleic  and  fumaric  acids  are  thus  seen  to  have 
precisely  the  same  composition ;  they  are  formed  by  the  separation  of  2  eq. 
of  water  from  hydrated  malic  acid. 

Tannic  and  gallic  acids.  — .These  are  substances  in  which  the  acid 
character  is  much  less  strongly  marked  than  in  the  preceding  bodies;  they 
constitute  the  astringent  principles  of  plants,  and  are  widely  diflpused,  in 
one  form  or  other,  through  the  vegetable  kingdom.  It  is  possible  that  there 
may  be  several  distinct  modifications  of  tannic  acid,  which  differ  among 
themselves  in  some  particulars.  The  astringent  pi-inciple  of  oak-bark  and 
nut-galls,  for  example,  is  found  to  precipitate  salts  of  sesquioxide  of  iron 
bluish-black,  while  that  from  the  leaves  ef  the  sumach  and  tea-plant,  ns 
well  as  infusions  of  the  substances  known  in  commerce  under  the  name  of 
kino  and  catechu,  are  remarkable  for  giving,  under  similar  circumstances, 
precipitates  which  have  a  tint  of  green.  The  colour  of  a  precipitate  is, 
however,  too  much  influenced  by  external  causes  to  be  relied  upon  as  a 
proof  of  essential  difference.  Unfortunately,  the  tannic  acid  or  acids  refuse 
to  crystallize;   one  most  valuable  test  of  individuality  is  therefore  lost. 

After  tlie  reaction  with  salts  of  sesquioxide  of  iron,  the  most  character- 
istic feature  of  tannic  acid  and  the  other  astringent  infusions  referred  to,  is 
that  of  forming  insoluble  compounds  with  a  great  variety  of  organic,  and 
especially  animal  substances,  as  solutions  of  starch  and  gelatin,  solid  mus- 
cular fibre  and  skin,  &c.,  which  then  acquire  ^he  property  of  resisting  putre- 


VEGETABLE    ACIDS. 


417 


Fig.  172. 


faction ;  it  is  on  this  principle  that  leather  is  manufactured.     Gallic  acid,  on 
the  contrary,  is  useless  in  the  operation  of  tanning. 

Tannic  Acid  of  the  Oak.  —  This  substance  may  be  prepared  by  the  elegant 
and  happy  method  of  M.  Pelouze,  from  nut-galls,  which  are 
excrescences  produced  on  the  leaves  of  a  species  of  oak,  the 
Quercus  infectoria,  by  the  puncture  of  an  insect.  A  glass 
vessel,  having  somewhat  the  figure  of  that  represented  in  the 
margin,  fig.  172,  is  loosely  stopped  at  its  lower  extremity  by 
a  bit  of  cotton  wool,  and  half  or  two-thirds  filled  with  pow- 
dered Aleppo-galls.  Ether,  prepared  in  the  usual  manner  by 
rectification,  and  containing,  as  it  invariably  does,  a  little 
water,  is  then  poured  upon  the  powder,  and  the  vessel  loosely 
stopped.  The  liquid,  which  after  some  time  collects  in  the 
receiver  below,  consists  of  two  distinct  strata ;  the  lowest, 
which  is  almost  colourless,  is  a  very  strong  solution  of  nearly 
pure  tannic  acid  in  water ;  the  upper  consists  of  ether  holding 
in  solution  gallic  acid,  colouring  matter,  and  other  impurities. 
The  carefully-separated  heavy  liquid  is  placed  to  evaporate 
over  a  surface  of  oil  of  vitriol  in  the  vacuum  of  the  air-pump. 
Tannic  acid,  or  tannin,  thus  obtained,  forms  a  slightly  yellowish, 
friable,  porous  mass,  without  the  slightest  tendency  to  crystal- 
lization. It  is  very  soluble  in  water,  less  so  in  alcohol,  and 
very  slightly  soluble  in  ether.  It  reddens  litmus,  and  pos- 
sesses a  pure  f  stringent  taste  without  bitterness. 

A  strong  solution  of  this  substance  mixed  with  mineral  acids 
gives  rise  to  precipitates,  which  consist  of  combinations  of  the 
tannic  acid  with  the  acids  in  question ;  these  compounds  are 
freely  soluble  in  pure  water,  but  scarcely  so  in  acid  solutions. 
Tannic  acid  precipitates  albumin,  gelatin,  salts  of  the  vegeto- 
alkalis,  and  several  other  substances ;  it  forms  soluble  com- 
pounds with  the  alkalis,  which,  if  excess  of  base  be  present,  rapidly  attract 
oxygen,  and  become  brown  by  destruction  of  the  acid;  the  tannates  of 
baryta,  strontia,  and  lime  are  sparingly  soluble,  and  those  of  the  oxides  of 
lead  and  antimony  insoluble.  Salts  of  protoxide  of  iron  are  unchanged  by 
solution  of  tannic  acid ;  salts  of  the  sesquioxide,  on  the  contrary,  give  with 
it  a  deep  bluish-black  precipitate,  which  is  the  basis  of  writing-ink ;  hence 
the  value  of  an  infusion  of  tincture  of  nut-galls  as  a  test  for  the  presence 
of  that  metal.  The  action  of  acids  upon  tannic  acid  gives  rise  to  the  for- 
mation of  gallic  acid,  which  will  be  presently  described,  with  simultaneous 
separation  of  grape-sugar.  Hence  tannic  acid  would  appear  to  be  a  conju- 
gated sugar-compound. 

Tannic  acid,  carefully  dried,  contains  CigHjOg-j-SHO.' 

Tannic  acid,  closely  resembling  that  obtained  from  galls,  may  be  extracted 
by  cold  water  from  catechu;  hot  water  dissolves  out  a  substance  having 
feeble  acid  properties,  termed  catechin.  This  latter  compound,  when  pure, 
crystallizes  in  fine  colourless  needles,  which  melt  when  heated,  and  dissolve 
very  freely  in  boiling  water,  but  scarcely  at  all  in  the  cold.  Catechin  dis- 
solves also  in  hot  alcohol  and  ether.  The  aqueous  solution  acquires  a  red 
tint  by  exposure  to  air,  and  precipitates  acetate  of  lead  and  corrosive  subli- 
mate white,  reduces  nitrate  of  silver  on  the  addition  of  ammonia,  but  fails 
to  form  insoluble  compounds  with  gelatin,  starch,  and  the  vegeto-alkalis.    It 


»  This  formula  is  scarcely  established  beyond  a  doubt.  M.  Strecker,  who  has  obseryed  the 
formation  of  sugar  from  tannic  acid,  represents  this  substance  by  the  formula  CioHisQagj  and 
its  change  under  the  influence  of  acids  by  the  equation 

2CwniH036+SH0        =        8(C'7H03,2HO)        -|-        Cu^H^Om 


Tannic  acid. 


Gallic  acid. 


Grape-BUgar. 


418  VEGETABLE    ACIDS. 

strikes  a  deep  green  colour  with  the  salts  of  sesquioxide  of  iron.  This  body 
is  said  to  be  convertible  by  heat  into  tannic  acid. 

The  formula  which  has  been  assigned  to  catechin  is  CjgHgOg. 

Japonic  and  ruhic  acids  are  formed  by  the  action  of  alkali  in  excess  upon 
catechin ;  the  first  in  the  caustic  condition,  and  the  second  when  in  the  state 
of  carbonate.  Japonic  acid  is  a  black  and  nearly  insoluble  substance,  so- 
luble in  alkalis  and  precipitated  by  acids,  containing  ^.^^fi^^fd ;  it  is  per- 
haps identical  with  a  black  substance  of  acid  properties,  formed  by  M. 
P61igot,  by  heating  grape-sugar  with  hydrate  of  baryta.  Rubic  acid  has  been 
but  little  studied ;  it  is  said  to  form  red  insoluble  compounds  with  the  earths 
and  certain  oxides  of  the  metals. 

Several  acids  closely  allied  to  tannic  acid  have  been  found  in  coffee  and 
Paraguay  tea. 

Gallic  acid. — Gallic  acid  is  not  nearly  so  abundant  as  tannic  acid ;  it  is 
produced  by  an  alteration  of  the  latter.  A  solution  of  tannic  acid  in  water 
exposed  to  the  air,  gradually  absorbs  oxygen,  and  deposits  crystals  of  gallic 
acid,  formed  by  the  destruction  of  the  tannic  acid.  The  simplest  method 
of  preparing  this  acid  in  quantity  is  to  take  powdered  nut-galls,  which, 
when  fresh  and  of  good  quality,  contain  30  or  40  per  cent,  of  tannic  acid, 
with  scarcely  more  than  a  trace  of  gallic,  to  mix  this  powder  with  water  to 
a  thin  paste,  and  to  expose  the  mixture  to  the  air  in  a  warm  situation  for 
the  space  of  two  or  three  months,  adding  water  from  time  to  time  to  replace 
that  lost  by  drying  up.  The  mouldy,  dark-coloured  mass  produced  may 
then  be  strongly  pressed  in  a  cloth,  and  the  solid  portion  boiled  in  a  con- 
siderable quantity  of  water.  The  filtered  solution  deposits  on  cooling  abun- 
dance of  gallic  acid,  which  may  be  drained  and  pressed,  and  finally  purified 
by  re-crystallization.  It  forms  small,  feathery,  and  nearly  colourless  crys- 
tals, which  have  a  beautiful  silky  lustre ;  it  requires  for  solution  100  parts 
of  cold,  and  only  3  parts  of  boiling  water ;  the  solution  has  an  acid  and  as- 
tringent taste,  and  is  gradually  decomposed  by  keeping.  Gallic  acid  does 
not  precipitate  gelatin  ;  with  salts  of  protoxide  of  iron  no  change  is  pro- 
duced, but  with  those  of  the  sesquioxide  a  deep  bluish-black  precipitate 
falls,  which  disappears  when  the  liquid  is  heated,  from  the  reduction  of  the 
sesquioxide  to  the  protoxide  at  the  expense  of  the  gallic  acid. 

The  salts  of  gallic  acid  present  but  little  interest ;  those  of  the  alkalis  are 
soluble,  and  readily  destroyed  by  oxidation  in  presence  of  excess  of  base, 
the  solution  acquiring  after  some  time  a  nearly  black  colour ;  the  gallates 
of  most  of  the  other  metallic  oxides  are  insoluble. 

Gallic  acid,  dried  at  212°  (100°C),  contains  07HO3,2HO;  the  crystals  con- 
tain an  additional  equivalent  of  water.  •  ' 

The  insoluble  residue  of  woody  fibre  and  other  matters  from  which  the 
gallic  acid  has  been  withdrawn  by  boiling  water,  contains  a  small  quantity 
of  another  acid  substance,  which  may  be  extracted  by  an  alkali,  and  after- 
wards precipitated  by  an  addition  of  hydrochloric  acid,  as  a  greyish  inso- 
luble powder.  It  contains  C7H2O4,  when  dried  at  248°  (120°C),  or  gallic 
acid  minus  1  eq.  of  water.  The  term  ellagic  acid  is  given  to  this  substance. 
M.  Pelouze  once  observed  its  conversion  into  ordinary  gallic  acid. 

The  conversion  of  tannic  into  gallic  acid  by  oxidation  is  accompanied  by 
a  disengagement  of  carbonic  acid,  the  volume  of  which  equals  that  of  the 
oxygen  absorbed :  the  oxidizing  action  must  therefore  be  confined  to  the  car- 
bon, and  may  perhaps  be  thus  represented : — 


1  eq.  tannic  acid  CjgHgOia)        ("2  eq.  gallic  acid  ....  C,4HgOjo 

I  = -I  2  eq.  water 

8  eq.  oxygen Og  j        (4  eq.  carbonic  acid 


water HjO  2 


VEGETABLE    ACIDS.  410 

Much  of  the  gallic  acid  is  subsequently  destroyed,  in  all  probability  onlj 
a  part  of  that  first  produced  escaping. 

The  changes  which  gallic  acid  suffers  when  exposed  to  heat  are  very  In- 
teresting. Heated  in  a  retort  by  means  of  an  oil-bath,  the  temperature  of 
which  is  steadily  maintained  at  420°  (215°C),  or  thereabouts,  it  is  resolved 
into  carbonic  acid,  and  a  new  acid  which  sublimes  into  the  neck  of  the  re- 
tort in  brilliant,  crystalline  plates,  of  the  most  perfect  whiteness ;  an  insig- 
nificant residue  of  black  matter. remains  behind.  The  term  pyrogallic  acid 
is  given  to  the  volatile  product.  It  dissolves  with  facility  in  water,  but  the 
solution  cannot  be  evaporated  without  blackening  and  decomposition;  it 
communicates  a  blackish-blue  colour  to  salts  of  the  protoxide  of  iron,  and 
reduces  those  of  the  sesquioxide  to  the  state  of  protoxide.  An  alkaline  so- 
lution of  this  acid  absorbs  a  very  considerable  quantity  of  oxygen,  and  has 
lately  been  employed  with  great  advantage  by  Professor  Liebig  for  the  pur- 
pose of  determining  the  amount  of  oxygen  in  atmospheric  air.  (See  page 
121.)  The  acid  characters  of  this  substance  are  very  indistinct.  Pyiogallic 
acid  contains  CgHgO^. 

When  dry  gallic  acid  is  suddenly  heated  to  480°  (249°C),  or  above,  it  is 
decomposed  into  carbonic  acid,  water,  and  a  second  new  acid,  the  metagallic, 
which  remains  in  the  retort  as  a  black,  shining  mass,  resembling  charcoal ; 
a  few  crystals  of  pyrogallic  acid  are  formed  at  the  same  time.  Metagallic 
acid  is  insoluble  in  water,  but  dissolves  in  alkalis,  and  is  again  precipitated 
as  a  black  powder  by  the  addition  of  an  acid.  It  combines  with  the  oxides 
of  lead  and  silver,  and  is  composed  of  CgHaOj.  Pyrogallic  acid,  also,  exposed 
to  the  requisite  temperature,  yields  metagallic  acid,  with  separation  of  water. 

Tannic  acid,  under  similar  circumstances,  furnishes  the  same  products  as 
gallic  acid.  Dr.  Stenhouse  has  shown  that  pyrogallic  acid  may  be  procured 
in  considerable  quantity  by  carefully  heating  the  dried  aqueous  extract  of 
gall-nuts  in  Dr.  Moh's  subliming  apparatus,  already  described.  All  these 
changes  admit  of  simple  explanation. 

C7H3O5         =         C6H3O3  4.     CO2 

Dry  gallic  acid.  Pyrogallic  acid. 

C8H3O3        =        CgH^Oj  4-     HO 

Pyrogallic  acid.  Metagallic  acid. 

^(CigHsOg.SHO)     =     6(C7H03,2HO)     +       2C6H3O3 

Tannic  acid.  Gallic  acid.  Pyrogallic  acid. 

These  phenomena  present  admirable  illustrations  of  the  production  of 
pyrogen-acids  by  the  agency  of  heat. 


420  CYANOGEN, 


SECTION    IV. 
AZOTIZED  ORGANIC  PRINCIPLES  OF  SIMPLE  CONSTITUTION. 


CYANOGEN,  ITS   COMPOUNDS    AND    DERIVATIVES., 

Cyanogen'  forms  the  most  perfect  type  of  a  quasi -simple  sub-radical  that 
chemistry  presents,  as  kakodyl  does  of  the  basyle  class ;  it  is  interesting 
also  from  being  the  first-discovered  body  of  the  kind. 

Cyanogen  may  be  prepared  with  the  utmost  ease  by  heating  in  a  small 
retort  of  hard  glass  the  salt  called  cyanide  of  mercury,  previously  reduced  to 
powder,  and  well  dried.  The  cyanide  undergoes  decomposition,  like  the 
oxide  under  similar  circumstances,  yielding  metallic  mercury,  a  small  quan- 
tity of  a  brown  substance  of  which  mention  will  again  be  made,  and  cyanogen 
itself,  a  colourless,  permanent  gas,  which  must  be  collected  over  mercury. 
It  has  a  pungent  and  very  peculiar  odour,  remotely  resembling  that  of  peach- 
kernels,  or  hydrocyanic  acid;  exposed  while  at  the  temperature  of  45° 
(7° -20)  to  a  pressure  of  3-6  atmospheres,  it  condenses  to  a  thin,  colourless, 
transparent  liquid.  Cyanogen  is  inflammable ;  it  burns  with  a  beautiful  pur- 
ple, or  peach-blossom  coloured  flame,  generating  carbonic  acid  and  liberating 
nitrogen.  The  specific  gravity  of  this  gas  is  1-806 ;  it  is  composed  of  carbon 
and  nitrogen  in  the  proportion  of  2  equivalents  of  the  former  to  1  equivalent 
of  the  latter,  or  CjN ;  this  is  easily  proved  by  mixing  it  with  twice  its  mea- 
sure of  pure  oxygen,  and  firing  the  mixture  in  the  eudiometer ;  carbonic  acid 
is  formed  equal  in  volume  to  the  oxygen  employed,  and  a  volume  of  nitrogen 
equal  to  that  of  the  cyanogen  is  set  free.  Cyanogen,  in  its  capacity  of  quasi-  • 
element,  is  designated  by  the  symbol  Cy.  Water  dissolves  4  or  5  times  its 
volume  of  cyanogen-gas,  and  alcohol  a  much  larger  quantity ;  the  solution 
rapidly  decomposes,  yielding  oxalate  of  ammonia,  C2N+4H0  =  NH40,C203, 
brown  insoluble  matter,  and  other  products. 

Paracyanogen.  —  This  is  the  brown  or  blackish  substance  above  referred 
to,  which  is  always  formed  in  small  quantity  when  cyanogen  is  prepared  by 
heating  the  cyanide  of  mercury,  and  probably  also,  by  the  decomposition  of 
solutions  of  cyanogen  and  of  hydrocyanic  acid.  It  is  insoluble  in  water  and 
alcohol,  is  dissipated  by  a  very  high  temperature,  and  contains,  according  to 
Professor  Johnson,  carbon  and  nitrogen  in  the  same  proportions  as  in  cya- 
nogen. 

Cyanide  of  hydrogen  ;  hydrocyanic  or  prussic  acid,  HCy. — This  very 
important  compound,  so  remarkable  for  its  poisonous  properties,  was  disco- 
vered as  early  as  1782,  by  Scheele.  It  may  be  prepared  in  a  state  of  purity, 
and  anhydrous,  by  the  following  process  :  A  long  glass  tube  filled  with  dry 
cyanide  of  mercury,  is  connected  by  one  extremity  with  an  arrangement  for 
furnishing  dry  sulphuretted-hydrogen  gas,  while  a  narrow  tube  attached  to 
the  other  end  is  made  to  pass  into  a  narrow-necked  phial  plunged  into  a 
freezing-mixture.     Gentle  heat  is  applied  to  the  tube,  the  contents  of  which 

*  So  called  from  Kvavoi,  blue,  and  ytvvdbi^l  generate. 


CYANOGEN.  421 

suffer  decomposition  in  contact  with  the  gas,  sulphide  of  mercury  and  cya- 
nide of  hydrogen  being  produced  ;  the  latter  is  condensed  in  the  receiver  to 
the  liquid  form.  A  little  of  the  cyanide  of  mercury  should  be  left  undecom- 
posed,  to  avoid  contamination  of  the  product  by  sulphuretted  hydrogen. 
The  pure  acid  is  a  thin,  colourless,  and  exceedingly  volatile  liquid,  which 
has  a  density  of  0-7058  at  45°  (7°-6C),  boils  at  79°  (26°-lC),  and  solidifies, 
when  cooled  to  0°  ( — 17°-8C) ;  its  odour  is  very  powerful  and  most  charac- 
teristic, much  resembling  that  of  peach-blossoms  or  bitter-almond  oil ;  it 
has  a  very  feeble  acid  reaction,  and  mixes  with  water  and  alcohol  in  all  pro- 
portions. In  the  anhydrous  state  this  substance  constitutes  one  of  the  most 
formidable  poisons  known,  and  even  when  largely  diluted  with  water,  its 
effects  upon  the  animal  system  are  exceedingly  energetic ;  it  is  employed, 
however,  in  medicine  in  very  small  doses.  The  inhalation  of  the  vapour 
should  be  carefully  avoided  in  all  experiments  in  which  hydrocyanic  acid  is 
concerned,  as  it  produces  headache,  giddiness,  and  other  disagreeable  symp- 
toms ;  ammonia  and  chlorine  are  the  best  antidotes. 

The  acid  in  its  pure  form  can  seldom  be  preserved ;  even  when  enclosed 
in  a  carefully-stopped  bottle  it  is  observed  after  a  very  short  time  to  darken, 
and  eventually  to  deposit  a  black  substance  containing  carbon,  nitrogen,  and 
perhaps  hydrogen ;  ammonia  is  formed  at  the  same  time,  and  many  other 
products.  Light  favours  this  decomposition.  Even  in  a  dilute  condition  it 
is  apt  to  decompose,  becoming  brown  and  turbid,  but  not  always  with  the 
same  facility,  some  samples  resisting  change  for  a  great  length  of  time,  and 
then  suddenly  solidifying  to  a  brown,  pasty  mass  in  a  few  weeks. 

When  hydrocyanic  acid  is  mixed  with  concentrated  mineral  acids,  the 
hydrochloric  for  example,  the  whole  solidifies  to  a  crystalline  paste  of  sal- 
ammoniac  and  hydrated  formic  acid ;  a  reaction  which  is  explained  in  a  very 
simple  manner,  1  eq.  of  hydrocyanic  acid  and  4  eq.  water,  yielding  1  eq.  of 
ammonia  and  1  eq.  of  formic  acid. 

CjN,H  +  4H0  =  NHg -f  C2H03,H0 

On  the  other  hand,  when  dry  formate  of  ammonia  is  heated  to  392° 
{ZOO°C),  it  is  almost  entirely  converted  into  hydrocyanic  acid  and  water. 
NH^O.CaHO,  ^  C2N,H  -}-  4H0. 

Aqueous  solution  of  hydrocyanic  acid  may  be  made  by  various  means. 
The  most  economical,  and  by  far  the  best,  where  considerable  quantities  are 
wanted,  is  to  decompose  at  a  boiling-heat  the  yellow  ferrocyanide  of  potas- 
eium  by  diluted  sulphuric  acid.  For  example,  500  grains  of  the  powdered 
ferrocyanide  may  be  dissolved  in  four  or  five  ounces  of  warm  water,  and 
introduced  into  a  capacious  flask  or  globe  capable  of  being  connected  by  a 
perforated  cork  and  wide  bent  tube  with  a  Liebig's  condenser  well  supplied 
with  cold  water ;  300  grains  of  oil  of  vitriol  are  diluted  with  three  or  fo\ir 
times  as  much  water  and  added  to  the  contents  of  the  flask ;  distillation  is 
carried  on  until  about  one-half  of  the  liquid  has  distilled  over,  after  which 
the  process  may  be  interrupted.  The  theory  of  this  process  has  been  care- 
fully studied  by  Mr.  Everitt ;  *  it  is  sufficiently  complicated. 

'  6  eq.  carbon  1:=:^  Insoluble  yellow  salt. 

6  eq.  carbon 

2  eq.  ferrocy-  3  eq.  nitrogen, 
anideof  po--^  3  eq.  nitrogen, 
tassium         |  1  eq.  potassium - 

I  3  eq,  potassiums 
\^2  eq.  iron 

3  ea   water      /  ^  ^^-  ^^y^^^ogen ^*^-- — ^^-3  gq.  hydrocyanic  acid. 

^  \  3  eq.  oxygen — — -__>^ 

6  eq.  sulphuric  acid -^*-  3  eq.  bisulphate  of  po- 

tassa. 

«6  •  Phil.  Magazine.  Feh.  1S35. 


422 


CYANOGEN, 


The  substance  described  in  the  preceding  diagram  as  insoluble  yellow  salt  le- 
mains  in  the  flask  after  the  reaction,  together  with  the  bisulphate  of  potassa ; 
it  contains  the  elements  of  2  eq.  cyanide  of  iron,  and  1  eq.  cyanide  potas- 
sium, but  its  constitution  is  unknown.  On  exposure  to  the  air,  it  rapidly 
becomes  blue. 

When  hydrocyanic  acid  is  wanted  for  purposes  of  pharmacy,  it  is  best  to 
prepare  a  strong  solution  in  the  manner  above  described,  and  then,  having 
ascertained  its  exact  strength,  to  dilute  it  with  pure  water  to  the  standard 
of  the  Pharmacopoeia,  viz.,  2  per  cent,  of  real  acid.  This  examination  is 
best  made  by  precipitating  with  excess  of  nitrate  of  silver  a  known  weight 
of  the  acid  to  be  tried,  collecting  the  insoluble  cyanide  of  silver  upon  a  small 
filter  previously  weighed,  washing,  drying,  and  lastly  re-weighing  the  whole. 
From  the  weight  of  the  cyanide  that  of  the  hydrocyanic  acid  can  be  easily 
calculated,  an  equivalent  of  the  one  corresponding  to  an  equivalent  of  the 
other ;  or  the  weight  of  the  cyanide  of  silver  may  be  divided  by  6,  which 
will  give  a  close  approximation  to  the  truth. 

Another  very  elegant  method  for  determining  the  amount  of  hydrocyanic 
acid  in  a  liquid  has  been  lately  suggested  by  Prof.  Liebig.  It  is  based  upon 
the  property  possessed  by  cyanide  of  potassium  of  dissolving  a  quantity  of 
chloride  of  silver  sufficient  to  produce  with  it  a  double  cyanide  containing 
equal  equivalents  of  cyanide  of  silver  and  of  potassium  (KCy,AgyCy).  Hence 
a  solution  of  hydrocyanic  acid,  which  is  super-saturated  with  potassa,  and 
mixed  with  a  few  drops  of  solution  of  common  salt,  will  not  yield  a  perma- 
nent precipitate  with  nitrate  of  silver  before  the  whole  of  the  hydrocyanic 
acid  is  converted  into  the  above  double  salt.  If  we  know  the  amount  of 
silver  in  a  given  volume  of  the  nitrate-solution,  it  is  easy  to  calculate  the 
quantity  of  hydrocyanic  acid,  for  this  quantity  will  stand  to  the  amount  of 
silver  in  the  nitrate  consumed,  as  2  eq.  of  hydrocyanic  acid  to  1  eq.  of 
silver,  i.  e. 

108  :  54  =  silver  consumed  :  z. 

It  is  a  common  remark,  that  the  hydrocyanic  acid  made  from  ferrocyanide 
of  potassium  keeps  better  thi»n  that  made  by  other  means.  The  cause  of 
this  is  ascribed  to  the  presence  of  a  trace  of  mineral  acid.  Mr.  Everitt  ac 
tually  found  that  a  few  drops  of  hydrochloric  acid,  added  to  a  large  bulk  of 
the  pure  dilute  acid,  preserved  it  from  decomposition,  while  another  portion, 
not  so  treated,  became  completely  spoiled. 

A  very  convenient  process  for  the  extemporaneous  preparation  of  an  acid 
of  definite  strength,  is  to  decompose  a  known  quantity  of  cyanide  of  potas- 
sium by  solution  of  tartaric  acid :  100  grains  of  crystallized  tartaric  acid  in 
powder,  44  grains  of  cyanide  of  potassium,  and  2  measured  ounces  of  distilled 
water,  shaken  up  in  a  phial  for  a  few  seconds,  and  then  left  at  rest,  in  order 
that  the  precipitate  may  subside,  will  yield  an  acid  of  very  nearly  the  required 
strength.  A  little  alcohol  may  be  added  to  complete  the  separation  of  the 
cream  of  tartar ;  no  filtration  or  other  treatment  need  be  employed. 

The  production  of  hydrocyanic  acid  from  bitter-almonds  has  been  already 
mentioned  in  connection  with  the  history  of  the  volatile  oil.  Bitter-almonds, 
the  kernels  of  plums  and  peaches,  the  seeds  of  the  apple,  the  leaves  of  the 
cherry-laurel,  and  various  other  parts  of  plants  belonging  to  the  great  natural 
order,  rosacece,  yield  on  distillation  with  water,  a  sweet-smelling  liquid,  con- 
taining hydrocyanic  acid.  This  is  probably  due  in  all  cases  to  the  decompo- 
sition of  the  amygdalin,  pre- existent  in  the  organic  structure.  The  change 
in  question  is  brought  about,  in  a  very  singular  manner,  by  the  presence  of 
a  soluble  azotized  substance,  called  emulsin  or  synaptase,  which  forms  a  large 
proportion  of  the  white  pulp  of  both  bitter  and  sweet  almonds.  This  sub- 
Btance  bears  a  somewhat  similar  relation  to  amygdalin,  that  diastase,  which 


ITS    COMPOUNDS    AND    DERIVATIVES.  423 

it  closely  resembles  in  many  particulars,  does  to  starch.  Hydrocyanic  acid 
exists  ready-formed  to  a  considerable  extent  in  the  juice  of  the  bitter  cassava. 

Amygdalin  is  prepared  with  facility  by  the  following  process :  —  The  paste 
of  bitter-almonds,  from  which  the  fixed  oil  has  been  expressed,  is  exhausted 
with  boiling  alcohol:  this  coagulates  and  renders  inactive  the  synaptase, 
while  at  the  same  time  it  dissolves  out  the  amygdalin.  The  alcoholic  liquid 
is  distilled  in  a  water-bath,  by  which  much  of  the  spirit  is  recovered,  and 
the  syrupy  residue  diluted  with  water,  mixed  with  a  little  yeast,  and  set  in 
a  warm  place  to  ferment ;  a  portion  of  sugar,  present  in  the  almonds,  is  thus 
destroyed.  The  filtered  liquid  is  then  evaporated  to  a  syrupy  state  in  a 
water-bath,  and  mixed  with  a  quantity  of  alcohol,  which  throws  down  the 
amygdalin  as  a  white  crystalline  powder ;  the  latter  is  collected  on  a  cloth 
filter,  pressed,  re-dissolved  in  boiling  alcohol,  and  left  to  cool.  It  separates 
in  small  crystalline  plates,  of  pearly  whiteness,  which  are  inodorous  and 
nearly  tasteless ;  it  is  decomposed  by  heat,  leaving  a  bulky  coal,  and  diffusing 
the  odour  of  the  hawthorn.  In  water,  both  hot  and  cold,  amygdalin  is  very 
insoluble :  a  hot  saturated  solution  deposits,  on  cooling,  brilliant  prismatic 
crystals,  which  contain  water.  In  cold  alcohol  it  dissolves  with  great  diffi- 
culty. Heated  with  dilute  nitric  acid,  or  a  mixture  of  dilute  sulphuric  acid 
and  binoxide  of  manganese,  it  is  resolved  into  ammonia,  bitter-almond  oil, 
benzoic  acid,  formic  acid,  and  carbonic  acid ;  with  permanganate  of  potassa, 
it  yields  a  mixture  of  cyanate  and  benzoate  of  that  base. 

Amygdalin  is  composed  of  C40H27NO22. 

Synaptase  itself  has  never  been  obtained  in  a  state  of  purity,  or  fit  for 
analysis ;  it  is  described  as  a  yellowish- white,  opaque,  brittle  mass,  very 
soluble  in  water,  and  coagulable,  like  albumin,  by  heat,  in  which  case  it 
loses  its  specific  property.  In  solution  it  very  soon  becomes  turbid  and  pu- 
trefies. The  decomposition  of  amygdalin  under  the  influence  of  this  body 
may  be  elegantly  studied  by  dissolving  a  portion  in  a  large  quantity  of  water, 
and  adding  a  little  emulsion  of  sweet-almond  ;  the  odour  of  the  volatile  oil 
immediately  becomes  apparent,  and  the  liquor  yields,  on  distillation,  hydro- 
cyanic acid.  The  nature  of  the  decomposition  may  be  thus  approximately 
represented : — 


1  eq.  amygdalin, 

C4oH2,N022 


1  eq.  hydrocyanic  acid  C  gH  N 

2  eq.  bitter-almond  oil  G2%^n   ^\ 

sugar C  gH^   0^ 

2  eq.  formic  acid  C  4H  ^   Og 

5  eq.  water  H  «   0= 


C.nH^NO 


22" 


It  may  be  observed  that  in  preparing  bitter-almond  oil  the  paste  should 
be  well  mixed  with  about  20  parts  of  warm  water,  and  the  whole  left  to 
stand  some  hours  before  distillation ;  the  heat  must  be  gently  raised  to  avoid 
coagulating  the  synaptase  before  it  has  had  time  to  act  upon  the  amygdalin. 
Almond-paste,  thrown  into  boiling  water,  yields  little  or  no  bitter-almond  oil. 

Amygdalic  acid. — When  amygdalin  is  boiled  with  an  alkali  or  an 
alkaline  earth,  it  is  decomposed  into  ammonia,  and  a  new  acid  called  the 
amygdalic,  which  remains  in  union  with  the  base.  This  is  best  prepared  by 
means  of  baryta-water,  the  ebullition  being  continued  as  long  as  ammonia 
is  evolved.  From  the  solution  thus  obtained,,  the  baryta  may  be  precipi- 
tated by  dilute  sulphuric  acid ;  the  filtered  liquid  is  evaporated  in  a  water- 
bath.  Amygdalic  acid  forms  a  colourless,  transparent,  amorphous  mass, 
very  soluble  in  water,  and  deliquescent  in  moist  air ;  the  solution  has  an 
acid  taste  and  reaction.     It  is  converted  by  oxidizing  agents  into  titter- 


424  CYANOGEN, 

almond  oil,  formic,  and  benzoic  acids.  The  amygdalates  are  mostly  soluble, 
but  have  been  but  little  studied ;  the  acid  contains  C4oH2g024,HO. 

The  presence  of  hydrocyanic  acid  is  detected  with  the  utmost  ease ;  it9 
remarkable  odour  and  high  degree  of  volatility  almost  sufficiently  charac- 
terize it.  With  solution  of  nitrate  of  silver  it  gives  a  dense  curdy  white  pre- 
cipitate, much  resembling  the  chloride,  but  differing  from  that  substance  in 
not  blackening  so  readily  by  light,  in  being  soluble  in  boiling  nitric  acid, 
and  in  suffering  complete  decomposition  when  heated  in  a  dry  state,  metallic 
silver  being  left ;  the  chloride,  under  the  same  circumstances,  merely  fuses, 
but  undergoes  no  chemical  change.  Tha  production  of  Prussian  blue  by 
"  Scheele's  test"  is  an  excellent  and  most  decisive  experiment,  which  may 
be  made  with  a  very  small  quantity  of  acid.  The  liquid  to  be  examined  is 
mixed  with  a  few  drops  of  solution  of  sulphate  of  protoxide  of  iron  and  an 
excess  of  caustic  potassa,  and  the  whole  exposed  to  the  air  for  10  or  15 
minutes,  with  agitation ;  hydrochloric  acid  is  then  added  in  excess,  which 
dissolves  the  oxide  of  iron,  and,  if  hydrocyanic  acid  be  present,  leaves 
Prussian  blue  as  an  insoluble  powder.  The  reaction  becomes  quite  intel- 
ligible when  the  production  of  a  ferrocyanide,  described  a  few  pages  hence, 
is  understood.     See  page  432. 

Another  elegant  process  for  detecting  hydrocyanic  acid  is  mentioned  in  the 
article  upon  hydrosulphocyanic  acid. 

The  most  important  of  the  metallic  cyanides  are  the  following ;  they  bear 
the  most  perfect  analogy  to  the  haloid-salts. 

Cyanide  of  Potassium,  KCy. — When  potassium  is  heated  in  cyanogen 
gas,  it  takes  fire  and  burns  in  a  very  beautiful  manner,  yielding  cyanide  of 
the  metal ;  the  same  substance  is  produced  when  potassium  is  heated  in  the 
vapour  of  hydrocyanic  acid,  hydrogen  being  liberated.  If  pure  nitrogen 
gas  be  transmitted  through  a  white-hot  tube,  containing  a  mixture  of  car- 
bonate of  potassa  and  charcoal,  a  considerable  quantity  of  cyanide  of  potas- 
sium is  formed,  which  settles  in  the  cooler  portions  of  the  tube  as  a  white 
amorphous  powder;  carbonic  oxide  is  at  the  same  time  extricated.  If 
azotized  organic  matter  of  any  kind,  capable  of  furnishing  ammonia  by 
destructive  distillation,  as  horn-shavings,  parings  of  hides,  &c.,  be  heated 
to  redness  with  carbonate  of  potassa  in  a  close  vessel,  a  very  abundant  pro- 
duction of  cyanide  of  potassium  results,  which  cannot  however  be  advan- 
tageously extracted  by  direct  means,  but  in  practice  is  always  converted 
into  ferrocyanide,  which  is  a  much  more  stable  substance,  and  crystallizes 
better. 

There  are  several  methods  by  which  cyanide  of  potassium  may  be  pre- 
pared for  use.  It  may  be  made  by  passing  the  vapour  of  hydrocyanic  acid 
into  a  cold  alcoholic  solution  of  potassa ;  the  salt  is  deposited  in  a  crystal- 
line form,  and  may  be  separated  from  the  liquid,  pressed  and  dried.  Ferro- 
cyanide of  potassium,  heated  to  whiteness  in  a  nearly  close  vessel,  evolves 
nitrogen  and  other  gases,  and  leaves  a  mixture  of  charcoal,  carbide  of  iron, 
and  cyanide  of  potassium,  which  latter  salt  is  not  decomposed  unless  the 
temperature  be  excessively  high.  Mr.  Donovan  recommends  the  use  in  this 
process  of  a  wrought-iron  mercury-bottle,  which  is  to  be  half  filled  with  the 
ferrocyanide,  and  arranged  in  a  good  air-furnace,  capable  of  giving  the 
requisite  degree  of  heat ;  a  bent  iron  tube  is  fitted  to  the  mouth  of  the 
bottle  and  made  to  dip  half  an  inch  into  a  vessel  of  water ;  this  serves  to 
give  exit  to  the  gas.  The  bottle  is  gently  heated  at  first,  but  the  tempera- 
ture ultimately  raised  to  whiteness ;  when  no  more  gas  issues,  the  tube  is 
stopped  with  a  cork,  and,  when  the  whole  is  completely  cold,  the  bottle  is 
cut  asunder  in  the  middle  by  means  of  a  chisel  and  sledge-hammer,  and  the 
pure  white  fused  salt  carefully  separated  from  the  black  spongy  mass  below, 
and  preserved  in  a  well-stopped  bottle ;  the  black  substance  contains  much 


ITS     COMPOUNDS     AND     DERIVATIVES.  425 

cyanide,  which  may  he  extracted  by  a  little  cold  water.  It  would  be  better, 
perhaps,  in  the  foregoing  process,  to  deprive  the  ferrocyanide  of  potassium 
of  its  water  of  crystallization  before  introducing  it  into  the  iron  vessel. 

Professor  Liebig  has  published  a  very  easy  and  excellent  process  for 
making  cyanide  of  potassium,  which  does  not,  however,  yield  it  pure,  but 
mixed  with  cyanate  of  potassa.  For  most  of  the  applications  of  cyanide 
of  potassium,  as,  for  example,  electro-plating  and  gilding,  for  which  a  con- 
siderable quantity  is  now  required,  this  impurity  is  of  no  consequence.  8 
parts  of  ferrocyanide  of  potassium  are  rendered  anhydrous  by  gentle  heat, 
and  intimately  mixed  with  3  parts  of  dry  carbonate  of  potassa ;  this  mix- 
ture is  thrown  into  a  red-hot  earthen  crucible,  and  kept  in  fusion,  with  occa- 
sional stirring,  until  gas  ceases  to  be  evolved,  and  the  fluid  portion  of  the 
mass  becomes  colourless.  The  crucible  is  left  at  rest  for  a  moment,  and 
then  the  clear  salt  decanted  from  the  heavy  black  sediment  at  the  bottom, 
which  is  principally  metallic  iron  in  a  state  of  minute  division.  In  this 
experiment,  2  eq.  of  ferrocyanide  of  potassium  and  2  eq.  carbonate  of 
potassa  yield  5  eq.  cyanide  of  potassium,  1  eq.'  cyanate  of  potassa,  2  eq. 
iron,  and  2  eq.  carbonic  acid.  The  product  may  be  advantageously  used, 
instead  of  ferrocyanide  of  potassium,  in  the  preparation  of  hydrated  hydro- 
cyanic acid,  by  distillation  with  diluted  oil  of  vitriol. 

Cyanide  of  potassium  forms  colourless,  cubic  or  octahedral  crystals,  deli- 
quescent in  the  air,  and  exceedingly  soluble  in  water ;  it  dissolves  in  boiling 
alcohol,  but  separates  in  great  measure  on  cooling.  It  is  readily  fusible,  and 
undergoes  no  change  at  a  moderate  red,  or  even  white-heat,  when  excluded 
from  air ;  otherwise,  oxygen  is  absorbed  and  the  cyanide  of  potassium 
becomes  cyanate  of  potassa.  Its  solution  always  has  an  alkaline  reaction, 
and  exhales  when  exposed  to  the  air  the  smell  of  hydrocyanic  acid ;  it  is 
decomposed  by  the  feeblest  acids,  even  the  carbonic  acid  of  the  atmosphere, 
and  when  boiled  in  a  retort  is  slowly  converted  into  formate  of  potassa  with 
separation  of  ammonia.  This  salt  is  anhydrous ;  it  is  said  to  be  as  poisonous 
as  hydrocyanic  acid  itself. 

Cyanide  of  potassium  has  been  derived  from  a  curious  and  unexpected 
source.  In  some  of  the  iron-furnaces  in  Scotland  where  raw-coal  is  used 
for  fuel  with  the  hot  blast,  a  saline-looking  substance  is  occasionally  observed 
to  issue  in  a  fused  state  from  the  tuyere-holes  of  the  furnace,  and  concrete 
on  the  outside.  This  proved,  on  examination  by  Dr.  Clark,  to  be  principally 
cyanide  of  potassium. 

Cyanide  of  soditjm,  NaCy,  is  a  very  soluble  salt,  corresponding  closely 
with  the  foregoing,  and  obtained  by  similar  means. 

Cyanide  of  ammonium,  NH4Cy.  —  This  is  a  colourless,  crystalHzable,  and 
very  volatile  substance,  prepared  by  distilling  a  mixture  of  cyanide  of  potas- 
sium and  sal-ammoniac,  or  by  mingling  the  vapour  of  anhydrous  hydrocyanic 
acid  with  ammoniacal  gas,  or,  lastly,  according  to  the  observation  of  M. 
Langlois,  by  passing  ammonia  over  red-hot  charcoal.  It  is  very  soluble  in 
water,  subject  to  spontaneous  decomposition,  and  is  highly  poisonous. 

Cyanide  of  mercury,  HgCy.  —  One  of  the  most  remarkable  features  in 
the  history  of  cyanogen  is  its  powerful  attraction  for  certain  of  the  less 
oxidable  metals,  as  silver,  and  more  particularly  mercury  and  palladium. 
Dilute  hydrocyanic  acid  dissolves  finely-powdered  red  oxide  of  mercury  with 
the  utmost  ease ;  the  liquid  loses  all  odour,  and  yields  on  evaporation  crys- 
tals of  cyanide  of  mercury.  Cyanide  of  potassium  is  in  like  manner  decom- 
posed by  red  oxide  of  mercury,  hydrate  of  potassa  being  produced.  Cyanide 
of  mercury  is  generally  prepared  from  common  ferrocyanide  of  potassium  , 
2  parts  of  the  salt  are  dissolved  in  15  parts  of  hot  water,  and  3  parts  of  dry 
sulphate  of  mercury  added ;  the  whole  is  boiled  for  15  minutes,  and  filtered 
hot  from  the  oxide  of  iron,  which  separates.  The  solution,  on  cooliug, 
iJ6  * 


i26  CYANOGEN, 

deposits  the  new  salt  in  crystals.  Cyanide  of  mercury  forms  white,  trans- 
lucent prisms,  much  resembling  those  of  corrosive  sublimate :  it  is  soluble 
in  8  parts  of  cold  water,  and  in  a  much  smaller  quantity  at  a  higher  tempe- 
rature, and  also  in  alcohol.  The  solution  has  a  disagreeable,  metallic  taste, 
is  very  poisonous,  and  is  not  precipitated  by  alkalis.  Cyanide  of  mercury  is 
used  in  the  laboratory  as  a  source  of  cyanogen. 

Cyanide  of  silver,  AgCy,  has  been  already  described.  Cyanide  of  zinc, 
ZnCy,  is  a  white  insoluble  powder,  pi-epared  by  mixing  acetate  of  zinc  with 
hydi'ocyanic  acid.  Cyanide  of  cobalt,  CoCy,  is  obtained  by  similar  means ; 
it  is  dirty  white,  and  insoluble.  Cyanide  of  palladium  forms  a  pale,  whitish 
precipitate  when  the  chloride  of  that  metal  is  mixed  with  a  soluble  cyanide, 
including  that  of  mercury.  Tercyanide  of  gold,  AuCyg,  is  yellowish-white 
and  insoluble,  but  freely  dissolved  by  solution  of  cyanide  of  potassium. 
Proiocyanide  of  iron  has  not  been  obtained,  from  the  tendency  of  the  metal 
to  pass  into  the  radical,  and  generate  a  ferrocyanide.  An  insoluble  green 
compound  containing  FeCy,F2Cy8  was  formed  by  M.  Pelouze  by  passing  chlo' 
rine  gas  into  a  boiling  solution  of  ferrocyanide  of  potassium. 

Cyanic  and  cyanuric  acids. — These  are  two  remarkable  isomeric  bodies, 
related  in  a  very  close  and  intimate  manner,  and  presenting  phenomena  of 
great  interest.  Cyanic  acid  is  the  true  oxide  of  cyanogen ;  it  is  formed  in 
conjunction  with  cyanide  of  potassium,  when  cyanogen  gas  is  transmitted 
over  heated  hydrate  or  carbonate  of  potassa,  or  passed  into  a  solution  of 
the  alkaline  base,  the  reaction  resembling  that  by  which  chlorate  of  potassa 
and  chloride  of  potassium  are  generated  when  the  oxide  and  the  salt-radical 
are  presented  to  each  other.  Cyanate  of  potassa  is,  moreover,  formed  when 
the  cyanide  is  exposed  to  a  high  temperature  with  access  of  air;  unlike  the 
chlorate,  it  bears  a  full  red-heat  without  decomposition. 

Ilydrated  Cyanic  Acid,  CyO,HO,  is  procured  by  heating  to  dull  redness  in 
a  hard  glass  retort  connected  with  a  receiver  cooled  by  ice,  cyanuric  acid, 
deprived  of  its  water  of  crystallization.  The  cyanuric  acid  is  resolved,  with- 
out any  other  product,  into  hydrated  cyanic  acid,  which  condenses  in  the 
receiver  to  a  limpid,  colourless  liquid,  of  exceedingly  pungent  and  penetra- 
ting odour,  like  that  of  the  strongest  acetic  acid ;  it"  even  blisters  the  skin. 
When  mixed  with  water,  it  decomposes  almost  immediately,  giving  rise  to 
bicarbonate  of  ammonia. 

C,NO,HO-f2HO=C204+NH8. 

This  is  the  reason  why  the  hydrated  acid  cannot  be  separated  from  a 
cyanate  by  a  stronger  acid.  A  trace  of  cyanic  acid,  however,  always  escapes 
decomposition,  and  communicates  to  the  carbonic  acid  evolved  a  pungent 
smell  similar  to  that  of  the  sulphurous  acid.  The  cyanates  may  be  easily 
distinguished  by  this  smell,  and  by  the  simultaneous  formation  of  an  ammo- 
nia-salt, which  remains  behind. 

The  pure  hydrated  cyanic  acid  cannot  be  preserved ;  shortly  after  its  pre- 
paration it  changes  spontaneously,  with  sudden  elevation  of  temperature, 
into  a  solid,  white,  opaque,  amorphous  substance,  called  cyamelide.  This 
curious  body  has  the  same  composition  as  hydrated  cyanic  acid  ;  it  is  inso- 
luble in  water,  alcohol,  ether,  and  dilute  acids ;  it  dissolves  in  strong  oil  ef 
vitriol  by  the  aid  of  heat,  with  evolution  of  carbonic  acid  and  production 
of  ammonia ;  boiled  with  solution  of  caustic  alkali,  it  dissolves,  ammonia  is 
disengaged,  and  a  mixture  of  cyanate  and  cyanurate  of  the  base  generated. 
By  dry  distillation  it  is  again  converted  into  the  hydrate  of  cyanic  acid. 

Cyanate  of  potassa,  KO,CyO.  —  The  best  method  of  preparing  this  salt, 
is,  according  to  Liebig,  to  oxidize  cyanide  of  potassium  by  means  of  litharge. 
The  cyanide,  already  containing  a  portion  of  cyanate,  described  p.  425,  is 
re-melted  in  an  earthen  crucible,  and  finely  powdered  protoxide  of  lead  adied 


ITS    COMPOUNDS    AND     DERIVATIVES.  427 

by  small  portions  ;  the  oxide  is  instantaneously  reduced,  and  the  metal,  at 
fii"st  in  a  state  of  minute  division,  ultimately  collects  to  a  fused  globule  at  the 
bottom  of  the  crucible.  The  salt  is  poured  out,  and,  when  cold,  powdered 
and  boiled  with  alcohol ;  the  hot  filtered  solution  deposits  crystals  of  cyanate 
of  potassa  on  cooling.  The  great  de-oxidizing  power  exerted  by  cyanide  of 
potassium  at  a  high  temperature  promises  to  render  it  a  valuable  agent  in 
many  of  the  finer  metallurgic  operations. 

Another  method  of  preparing  the  cyanide  is  to  mix  dried  and  finely-pow- 
dered ferrocyanide  of  potassium  with  half  its  weight  of  equally  dry  binoxide 
of  manganese  ;  to  heat  this  mixture  in  a  shallow  iron  ladle  with  free  expo- 
sure to  air  and  frequent  "stirring  until  the  tinder-like  combustion  is  at  an  end, 
and  to  boil  the  residue  in  alcohol,  which  extracts  the  cyanate  of  potassa. 

This  salt  crystallizes  from  alcohol  in  thin,  colourless,  transparent  plates, 
which  suffer  no  change  in  dry  air,  but  on  fexposure  to  moisture  become  gra- 
dually converted,  without  much  alteration  of  appearance,  into  bicarbonate 
of  potassa,  ammonia  being  at  the  same  time  disengaged.  Water  dissolves  the 
cyanate  of  potassa  in  large  quantity ;  the  solution  is  slowly  decomposed  in 
the  cold,  and  rapidly  at  a  boiling  heat,  into  bicarbonate  of  potassa  and  am- 
monia. When  a  concentrated  solution  is  mixed  with  a  small  quantity  of 
dilute  mineral  acid,  a  precipitate  falls,  which  consists  of  acid  cyanurate  of 
potassa.  Cyanate  of  potassa  is  reduced  to  cyanide  of  potassium  by  ignition 
with  charcoal  in  a  covered  crucible. 

Cyanate  of  potassa,  mixed  with  solutions  of  lead  and  silver,  gives  rise  to 
insoluble  cyanates  of  the  oxides  of  those  metals,  which  are  white. 

Cyanate  of  ammonia  ;  urea.  —  When  the  vapour  of  hydrated  cyanic  acid 
is  mixed  with  excess  of  ammoniacal  gas,  a  white,  crystalline,  solid  substance 
is  produced,  which  has  all  the  characters  of  a  true,  although  not  neutral, 
cyanate  of  ammonia.  It  dissolves  in  water,  and,  if  mixed  with  an  acid,  evolves 
carbonic  acid  gas ;  with  an  alkali,  it  yields  ammonia.  If  the  solution  be 
heated,  or  if  the  crystals  be  merely  exposed  a  certain  time  to  the  air,  a  por- 
tion of  ammonia  is  dissipated,  and  the  properties  of  the  compound  completely 
changed.  It  may  now  be  mixed  with  acids  without  the  least  symptoms  of 
decomposition,  while  cold  caustic  alkali,  on  the  other  hand,  fails  to  discharge 
the  smallest  trace  of  ammonia.  The  result  of  this  curious  metamorphosis  of 
the  cyanate  is  a  substance  called  urea,  a  product  of  the  animal  body,  the 
chief  and  characteristic  constituent  of  urine.  This  artificial  formation  of  one 
of  the  products  of  organic  life  cannot  fail  to  possess  great  interest.  Its  dis- 
covery is  due  to  Prof.  Wohler.  The  properties  of  urea,  and  the  most  advan- 
tageous methods  of  preparing  it,  will  be  found  described  a  few  pages  hence, 

Cyanuric  acid.  —  The  substance  called  melam,  of  which  farther  mention 
will  be  made,  is  dissolved  by  gentle  heat  in  concentrated  sulphuric  acid,  the 
solution  mixed  with  20  or  30  parts  of  water,  and  the  whole  maintained  at  a 
temperature  approaching  the  boiling-point,  until  the  specimen  of  the  liquid, 
on  being  tried  by  ammonia,  no  longer  gives  a  white  precipitate  :  several  days 
are  required.  The  liquid,  concentrated  by  evaporation,  deposits  on  cooling 
cyanuric  acid,  which  is  purified  by  re-crystallization.  Another,  and  perhaps 
simpler  method,  is  to  heat  dry  and  pure  urea  in  a  flask  or  retort ;  the  sub- 
stance melts,  boils,  disengages  ammonia  in  large  quantity,  and  at  length 
becomes  converted  into  a  dirty  white,  solid,  amorphous  mass,  which  is  impure 
cyanuric  acid.  This  is  dissolved  by  the  aid  of  heat  in  strong  oil  of  vitriol, 
and  nitric  acid  added  by  little  and  little  until  the  liquid  becomes  nearly 
colourless ;  it  is  then  mixed  with  water,  and  suffered  to  cool,  whereupon  the 
cyanuric  acid  separates.  The  urea  may  likewise  be  decomposed  very  con- 
veniently by  gently  heating  it  in  a  tube,  while  dry  chlorine  gas  passes  over 
it.  A  mixture  of  cyanuric  acid  and  sal-ammoniac  results,  which  is  separated 
by  dissolving  in  water. 


428  CYANOGEN, 

CyaBuric  acid  in  a  pure  state  forms  colourless  crystals,  seldom  of  large 
size,  derived  from  an  oblique  rhombic  prism,  -which  eflBoresce  in  a  dry  atmo- 
sphere from  loss  of  water.  It  is  very  soluble  in  cold  water,  and  requires  24 
parts  for  solution  at  a  boiling  heat;  it  reddens  litmus  feebly,  has  no  odour, 
and  but  little  taste.  This  acid  is  tribasic ;  the  crystals  contain  CgNgOj.SHO 
-}-4H0,  and  are  easily  deprived  of  the  4  eq.  of  water  of  crystallization.  In 
point  of  stability,  it  offers  a  most  remarkable  contrast  to  its  isomer,  cyanio 
acid  ;  it  dissolves,  as  above  indicated,  in  hot  oil  of  vitriol,  and  even  in  strong 
nitric  acid,  without  decomposition,  and  in  fact  crystallizes  from  the  latter  in 
an  anhydrous  state,  containing  CgNjOgjSHO.  Long-continued  boiling  with 
these  powerful  agents  resolves  it  into  ammonia  and  carbonic  acid. 

The  connection  between  cyanic  acid,  urea,  and  cyanuric  acid  may  be  thus 
recapitulated : — 

Cyanate  of  ammonia  is  converted  by  heat  into  urea. 
Urea  is  decomposed  by  the  same  means  into  cyanuric  acid  and  urea. 
Cyanuric  acid  is  changed  by  a  very  high  temperature  into  hydrated  cyanic 
acid. 

In  the  latter  reaction,  1  eq.  of  hydrated  cyanuric  acid  splits  into  3  eq.  hy- 
drated cyanic  acid. 

C6N303,3HO=3(CaNO,HO). 

Cyanate  and  cyanurate  of  oxide  of  ethyl.  —  If  a  dry  mixture  of  cya- 
nate of  potassa  and  sulphovinate  of  potassa  be  distilled,  a  product  is  ob- 
tained which  consists  of  a  mixture  of  the  above  ethers.  They  are  separated 
without  difificulty,  the  cyanate  boiling  at  140°  (60°C),  while  the  boiling  point 
of  the  eyanurat.e  is  much  higher,  namely,  528° -8  (276°C).  Cyanate  of  ethyl 
is  a  mobile  liquid,  the  vapour  of  which  excites  a  flow  of  tears.  The  com- 
position of  cyanate  of  ethyl  is  C6H5N02=C4lT50,C2NO=AeO,CyO.  The 
formation  is  represented  by  the  equation  KO,CyO-f-KO,AeO,2S03=AeO, 
CyO-j-2(KO,SO,).  The  cyanurate  of  ethyl  contains  SAeOjCgNgOg;  it  arises 
in  this  reaction  from  the  coalescence  of  3  eq.  of  cyanate  of  ethyl.  It  may 
be  likewise  obtained  by  distilling  a  mixture  of  sulphovinate  of  potassa  with 
cyanurate  of  potassa.  Cyanurate  of  ethyl  is  a  crystalline  mass,  slightly  so- 
luble in  water,  readily  soluble  in  alcohol  and  ether,  fusing  at  185°  (85°C). 
By  substituting  for  sulphovinate  of  potassa,  salts  of  sulphomethylic  and  sul- 
phamylic  acid,  the  corresponding  methyl-  and  amyl-compounds  may  be  ob- 
tained. 

The  study  of  the  cyanic  and  cyanuric  ethers,  which  were  discovered  by 
Wurtz,  has  led  to  very  important  results,  which  will  be  fully  described  in  the 
section  on  the  organic  bases. 

FuLMiNic  ACID. — This  remarkable  compound,  which  is  isomeric  both  with 
cyanic  and  cyanuric  acids,  originates  in  the  peculiar  action  exercised  by  ni- 
trous acid  upon  alcohol  in  presence  of  a  salt  of  silver  or  mercury.  Neither 
absolute  fulminic  acid  nor  its  hydrate  has  ever  been  obtained. 

Fulminate  of  silver  is  pi*epared  by  dissolving  40  or  50  grains  of  silver, 
which  need  not  be  pure,  in  f  oz.  by  measure  of  nitric  acid  of  sp.  gr.  1-37  or 
thereabouts,  by  the  aid  of  a  little  heat;  a  sixpence  answers  the  purpose  very 
well.  To  the  highly  acid  solution,  while  still  hot,  2  measured  ounces  of  al- 
cohol are  added,  and  heat  applied  until  reaction  commences.  The  nitric  acid 
oxidizes  part  of  the  alcohol  to  aldehyde  and  oxalic  acid,  becoming  itself  re- 
duced to  nitrous  acid,  which  in  turn  acts  upon  the  alcohol  in  such  a  manner 
as  to  form  nitrous  ether,  fulminic  acid,  and  water,  1  eq.  nitrous  ether  and 
1  eq.  of  nitious  acid  containing  the  elements  of  1  eq.  fulminic  acid  and  5 
eq.  water. 

C4H50,N0,-f  N03==:C,No024-5HO. 


ITS    COMPOUNDS    AND    DERIVATIVES.  4ii^ 

The  fulminate  of  silver  slowly  separates  from  the  hot  liquid  in  the  form 
of  small,  brilliant,  white,  crystalline  plates,  which  may  be  washed  with  a 
little  cold  water,  distributed  upon  separate  pieces  of  filter-paper  in  portions 
not  exceeding  a  grain  or  two  each,  and  left  to  dry  in  a  warm  place.  When 
dry,  the  papers  are  folded  up  and  preserved  in  a  box  or  bottle.  This  is  the 
only  safe  method  of  keeping  the  salt.  Fulminate  of  silver  is  soluble  in  36 
parts  of  boiling  water,  but  the  greater  part  crystallizes  out  on  cooling ;  it  is 
one  of  the  most  dangerous  substances  to  handle  that  chemistry  presents ;  it 
explodes  when  strongly  heated,  or  when  rubbed  or  struck  with  a  hard  body, 
or  when  touched  with  concentrated  sulphuric  acid,  with  a  degree  of  violence 
almost  indescribable ;  the  metal  is  reduced,  and  a  large  volume  of  gaseous 
matter  suddenly  liberated.  Strange  to  say,  it  may,  when  very  cautiously 
mixed  with  oxide  of  copper,  be  burned  in  a  tube  with  as  much  facility  as 
any  other  organic  substance.  Its  composition  thus  determined  is  expressed 
in  the  formula  2AgO,C4N202. 

The  acid  is  evidently  bibasic ;  when  fulminate  of  silver  is  digested  with 
caustic  potassa,  one-half  of  the  oxide  is  precipitated,  and  a  compound  pro- 
duced containing  AgO,KO,C4N20j|,  which  resembles  the  neutral  silver-salt, 
and  detonates  by  a  blow.  Corresponding  compounds  containing  soda  and 
oxide  of  ammonium  exist ;  but  a  pure  fulminate  of  an  alkaline  metal  has 
never  been  formed.  If  fulminate  of  silver  be  digested  with  water  and  cop- 
per, or  zinc,  the  silver  is  entirely  displaced,  and  a  fulminate  of  the  new  metal 
produced.  The  zinc-salt  mixed  with  baryta-water  gives  rise  to  a  precipitate 
of  oxide  of  zinc,  while  fulminate  of  zinc  and  baryta,  ZnO,BaO,C4N202,  re- 
mains in  solution.  Fulminate  of  mercury  is  prepared  by  a  process  very 
similar  to  that  by  which  the  silver-salt  is  obtained ;  one  part  of  mercury  is 
dissolved  in  12  parts  of  nitric  acid,  and  the  solution  mixed  with  an  equal 
quantity  of  alcohol ;  gentle  heat  is  applied,  and  if  the  reaction  becomes  too 
violent,  it  may  be  moderated  by  the  addition  from  time  to  time  of  more 
spirit,  much  carbonic  acid,  nitrogen,  and  red  vapours  are  disengaged,  to- 
gether with  a  large  quantity  of  nitrous  ether  and  aldehyde ;  these  are  some- 
times condensed  and  collected  for  sale,  but  are  said  to  contain  hydrocyanic 
acid.  The  fulminate  of  mercury  separates  from  the  hot  liquid,  and  after 
cooling  may  be'purified  from  an  admixture  of  reduced  metal  by  solution  in 
boiling  water  and  re-crystallization.  It  much  resembles  the  silver-salt  in 
appearance,  properties,  and  degree  of  solubility,  and  contains  2Hg20,C4N202. 
It  explodes  violently  by  friction  or  percussion,  but,  unlike  the  silver-corn, 
pound,  merely  burns  with  a  sudden  and  almost  noiseless  flash  when  kindled 
in  the  open  air.  It  is  manufactured  on  a  large  scale  for  the  purpose  of 
charging  percussion-caps ;  sulphur  and  chlorate  of  potassa,  or  more  fre- 
quently nitre,  are  added,  and  the  powder,  pressed  into  the  cap,  is  secured 
by  a  drop  of  varnish. 

The  relations  of  composition  between  the  three  isomeric  acids  are  beauti 
fully  seen  by  comparing  their  silver-salts ;  the  first  acid  is  monobasic,  the 
second  bibasic,  and  the  third  tribasic. 

Cyanate  of  silver AgO  ,  CjN  0. 

Fulminate  of  silver 2AgO  ,  C^^^'^i- 

Cyanurate  of  silver 3AgO  ,  CgNgOg. 

Until  quite  recently,  beyond  the  accidental  one  of  identity  of  composition, 
no  relation  existed  between  fulminic  acid  and  its  isomers.  Mr.  Gladstone 
has,  however,  shown  that,  when  a  solution  of  fulminate  of  copper  is  mixed 
with  excess  of  ammonia,  filtered,  treated  with  sulphuretted  hydrogen  in 
excess,  and  again  filtered  from  the  insoluble  sulphide  of  copper,  the  liquid 
obtained  is  a  mixed  solution  of  urea  and  sulphocyanide  of  ammonium. 

Chlorides  of  cyanogen.  —  Chlorine  forms  two  compounds  with  cyanogen 


430         FERROCYANOQEN    AND    ITS    COMPOUNDS. 

or  its  elements,  which  are  isomeric,  and  correspond  to  cyanic  and  cyanuric 
acids.  Gaseous  chloride  of  cyanogen,  CyCl,  is  formed  by  conducting  chlorine 
gas  into  strong  hydrocyanic  acid,  or  by  passing  chlorine  over  moist  cyanide 
of  mercury  contained  in  a  tube  sheltered  from  the  light.  It  is  a  permanent 
and  colourless  gas  at  the  temperature  of  the  air,  of  insupportable  pungency, 
and  soluble  to  a  very  considerable  extent  in  water,  alcohol,  and  ether.  At 
0°  ( — 17°'8C)  it  congeals  to  a  mass  of  colourless  crystals,  which  at  6° 
( — 15°C)  melt  to  a  liquid  whose  boiling-point  is  11°  ( — llo-6C).  At  the  tem- 
perature of  the  air  it  is  condensed  to  the  liquid  form  under  a  pressure  of 
four  atmospheres,  and  when  long  preserved  in  this  condition  in  hermetically- 
sealed  tubes  it  gradually  passes  into  the  solid  modification.  Solid  chloride 
of  cyanogen  is  generated  when  anhydrous  hydrocyanic  acid  is  put  into  a 
vessel  of  chlorine  gas,  and  the  whole  exposed  to  the  sun ;  hydrochloric  acid 
is  formed  at  the  same  time.  It  forms  long  colourless  needles,  which  exhale 
a  powerful  and  ofi'ensive  odour,  compared  by  some  to  that  of  the  excrement 
of  mice  ;  it  melts  at  284°  (140°C),  and  sublimes  unchanged  at  a  higher  tem- 
perature. When  heated  in  contact  with  water,  it  is  decomposed  into  cyanuric 
and  hydrochloric  acids.  This  compound  may  be  represented  by  the  formula 
CyoClg,  or  CgNgjClg.  It  dissolves  in  alcohol  and  ether  without  decomposition. 
Bromide  and  iodide  of  cyanogen  correspond  to  the  first  of  the  preceding 
compounds,  and  are  prepared  by  distilling  bromine  or  iodine  with  cyanide 
of  mercury.  They  are  colourless,  volatile,  solid  substances,  of  powerful 
odour. 

FERROCYANOGEN    AND   ITS    COMPOUNDS. 

When  a  solution  of  cyanide  of  potassium  is  digested  with  iron-filings  at  a 
gentle  heat  in  an  open  vessel,  oxygen  is  absorbed  from  the  air,  the  iron  dis- 
solves quietly  and  disappears,  and  a  highly  alkaline,  yellow  liquid  is  obtained, 
which  on  evaporation  deposits  lemon-yellow  crystals  containing  potassium  in 
combination  with  a  new  salt-radical  composed  of  the  metal  iron  and  the  ele- 
ments of  cyanogen ;  in  the  mother-liquid  hydrate  of  potassa  is  found.  3  eq. 
cyanide  of  potassium,  1  eq.  iron,  and  1  eq.  oxygen,  yield  1  eq.  of  the  new 
salt,  and  1  eq.  of  potassa. 

3KCy-f  Fe-l-0  =  KO+Kg.CgNgFe. 

The  new  substance  is  called  ferrocyanogen,  and  is  designated  by  the  symbol 
Cfy ;  it  is  bibasic,  neutralizing  2  equivalents  of  metal  or  hydrogen,  and  con- 
tains the  elements  of  3  equivalents  of  cyanogen  combined  with  1  eq.  of  iron. 
It  has  never  been  isolated. 

When  iron  in  filings  is  heated  in  a  small  retort  with  a  solution  of  cyanide 
of  potassium,  it  is  dissolved  with  evolution  of  hydrogen,  caustic  potassa  and 
the  new  substance  being  generated ;  the  oxygen  in  this  easels  derived  from 
the  decomposition  of  water.  Sulphide  of  iron  and  cyanide  of  potassium  give 
rise,  under  similar  circumstances,  to  sulphide  of  potassium  and  ferrocyanide 
of  potassium. 

Hydroferrocyanio  ACID,  Cfy2H.  —  Ferrocyanide  of  lead  or  copper,  both 
of  which  are  insoluble,  may  be  suspended  in  water,  and  decomposed  by  a 
stream  of  sulpluiretted  hydrogen  gas.  The  filtered  solution,  evaporated  in 
the  vacuum  of  the  air-pump  over  a  surface  of  oil  of  vitriol,  furnishes  the  acid 
in  a  solid  form.  If  the  aqueous  solution  be  agitated  with  ether,  nearly  the 
whole  of  the  acid  sej^arates  in  colourless,  crystalline  laminie ;  it  may  even 
be  made  in  large  quantity  by  adding  hydrochloric  acid  to  a  strong  solution 
of  ferrocyanide  of  potassium  in  water  free  from  air,  and  shaking  the  whole 
with  fether.  The  crystals  may  be  dissolved  in  alcohol,  and  the  acid  again 
thrown  down  by  ether,  which  possesses  the  remarkable  property  of  precipi- 
tating this  subotance  from  solution.  Hydroferrocyanic  acid  differs  completely 


PERROCTANOQEN    AND    ITS    COMPOUNDS.         431 

from  hydrocyanic  acid ;  its  solution  in  water  has  a  powerfully  acid  taste  and 
reaction,  and  decomposes  alkaline  carbonates  with  eflFervescence ;  it  refuses 
to  dissolve  oxide  of  mercury  in  the  cold,  but  when  heat  is  applied,  undergoes 
decomposition,  forming  cyanide  of  mercury  and  a  peculiar  compound  of  iron, 
cyanogen,  and  oxygen,  with  reduction  of  some  of  the  oxide.  In  a  dry  state 
the  acid  is  very  permanent,  but  when  long  exposed  to  the  air  in  contact  with 
water  it  becomes  entirely  converted  into  Prussian  blue.  This  interesting 
substance  was  discovered  by  Mr.  Porrett. 

Ferrocyanide  of  potassium,  frequently  called  Yellow  prussiate  of  potash, 
KgCfy+SHO,  or  KgCgNgFe-f-SHO.— This  most  beautiful  salt  is  manufactured 
on  a  large  scale  by  the  following  process,  which  will  now  be  easily  intelligi- 
ble : — Dry  refuse  animal  matter  of  any  kind  is  fused  at  a  red-heat  with  im- 
pure carbonate  of  potassa  and  some  iron-filings  in  a  large  iron  vessel,  from 
which  the  air  should  be  excluded  as  much  as  possible ;  cyanide  of  potassium 
is  generated  in  large  qtiantity.  The  melted  mass  is  afterwards  treated  with 
hot  water,  which  dissolves  out  the  cyanide  and  other  salts ;  the  cyanide  being 
quickly  converted  by  the  oxide  or  sulphide '  of  iron  into  ferrocyanide.  The 
filtered  solution  is  evaporated,  and  the  first-formed  crystals  purified  by  re- 
solution. If  a  sufficient  quantity  of  iron  be  not  present,  great  loss  is  incurred 
by  the  decomposition  of  the  cyanide  into  formate  of  potassa  and  ammonia. 

Ferrocyanide  of  potassium  forms  large,  transparent,  yellow  crystals, 
derived  from  an  octahedron  with  a  square  base ;  they  cleave  with  facility  in 
a  direction  parallel  to  the  base  of  the  octahedron,  and  are  tough  and  diffi- 
cult to  powder.  They  dissolve  in  4  parts  of  cold,  and  in  2  of  boiling  water, 
and  are  insoluble  in  alcohol.  They  are  permanent  in  the  air,  and  have  a 
mild  saline  taste.  The  salt  has  no  poisonous  properties,  and  in  small  doses, 
at  least,  is  merely  purgative.  Exposed  to  a  gentle  heat,  it  loses  3  eq.  of 
water,  and  becomes  anhydrous ;  at  a  high  temperature  it  yields  cyanide  of 
potassium,  carbide  of  iron,  and  various  gaseous  products ;  if  air  be  ad- 
mitted, the  cyanide  becomes  cyanate. 

The  ferrocyanides  are  often  described  as  double  salts  in  which  protocy- 
anide  of  iron  is  combined  with  other  metallic  cyanides,  or  with  hydrogen. 
Thus,  hydroferrocyanic  acid  is  written  FeCy,2IICy,  and  ferrocyanide  of 
potassium,  FeCy,2KCy-f-3HO;  the  oxygen  and  hydrogen  of  the  water  of 
crystallization  being  respectively  adequate  to  convert  the  metals  into  pro- 
toxide and  the  cyanogen  into  hydrocyanic  acid.  This  view  has  the  merit  of 
simplicity,  and  will  often  prove  an  useful  aid  to  the  memory,  but  there  are 
insuperable  objections  to  its  adoption  as  a  sound  and  satisfactory  theory, 

Ferrocyanide  of  potassium  is  a  chemical  reagent  of  great  value;  when 
mixed  in  solution  with  neutral  or  slightly  acid  salts  of  the  metals  proper,  it 
gives  rise  to  precipitates  which  very  frequently  present  highly  characteristic 
colours.  In  moit  of  these  compounds  the  potassium  of  the  base  is  simply 
displaced  by  the  new  metal :  the  beautiful  brown  ferrocyanide  of  copper 
contains,  for  example,  CugCfy  or  CugCgNgFe,  and  that  of  lead,  PbgCfy.  With 
salts  of  protoxide  of  iron  it  gives  a  bluish  precipitate,  which  becomes 
rapidly  dark  blue  by  exposure  to  air ;  this  appears  to  be  a  compound  of  the 
neutral  ferrocyanide  of  iron,  FcgCfy,  with  ferrocyanide  of  potassium. 

When  a  ferrocyanide  is  added  to  a  solution  of  salt  of  sesquioxide  oi  iron, 
Prussian  blue  is  produced.  Although  this  remarkable  substance  has  now 
been  long  known,  and  many  elaborate  researches -have  been  made  with  a 
view  of  determining  its  exact  composition,  the  problem  cannot  yet  be  said 
to  be  completely  solved.  This  difficulty  arises  in  gi-eat  measure  from  the 
existence  of  several  distinct  deep  blue  compounds  formed  under  different  cir- 

*  The  sulphur  is  derived  from  the  reduced  sulphate  of  the  crude  pearl-asl***  i'«^  in  thi* 
aaxLufacture. 


432         PERROCYANOGEN   AN  D     ITS    COMPOUNDS. 

cumstances,  and  having  many  properties  in  common,  which  have  been  fre- 
quently confounded.  The  following  is  a  summary  of  the  account  given  by 
Berzelius,  who  has  paid  much  attention  to  this  subject. 

Ordinary  Prussian  Blue,  CjgNgFe^,  or  Fe^Cfyg.  —  This  is  best  prepared  by 
adding  nitrate  of  sesquioxide  of  iron  to  solution  of  ferrocyanide  of  potas- 
sium, keeping  the  latter  in  slight  excess.  It  forms  a  bulky  precipitate  of 
the  most  intense  blue,  which  shrinks  to  a  comparatively  small  compass 
when  well  washed  and  dried  by  gentle  heat.  In  a  dry  state  it  is  hard  and 
brittle,  much  resembling  in  appearance  the  best  indigo  ;  the  fresh-fractured 
surfaces  have  a  beautiful  copper-red  lustre,  similar  to  that  produced  by 
rubbing  indigo  with  a  hard  body.  Prussian  blue  is  quite  insoluble  in  water 
and  dilute  acids,  with  the  exception  of  oxalic  acid,  in  a  solution  of  which  it 
dissolves,  forming  a  deep  blue  liquid,  which  is  sometimes  used  as  ink ;  con- 
centrated oil  of  vitriol  converts  it  into  a  white,  pasty  mass,  which  again 
becomes  blue  on  the  addition  of  water.  Alkalis  destroy  the  colour  in- 
stantly ;  they  dissolve  out  a  ferrocyanide,  and  leave  sesquioxide  of  iron. 
Boiled  with  water  and  red  oxide  of  mercury,  it  yields  a  cyanide  of  the 
metal,  and  sesquioxide  of  iron.  Heated  in  the  air,  Prussian  blue  burns 
like  tinder,  leaving  a  residue  of  sesquioxide  of  iron.  Exposed  to  a  high 
temperature  in  a  close  vessel,  it  disengages  water,  cyanide  of  ammonium, 
and  carbonate  of  ammonia,  and  leaves  carbide  of  iron.  This  substance 
forms  a  very  beautiful  pigment,  both  an  oil  and  a  water-colour,  but  has 
little  permanency.  The  Prussian  blue  of  commerce  is  always  exceedingly 
impure ;  it  contains  alumina  and  other  matters,  which  greatly  diminish  the 
brilliancy  of  the  colour. 

The  production  of  Prussian  blue  by  mixing  sesquioxide  salt  of  iron  and 
ferrocyanide  of  potassium  or  sodium  may  thus  be  elucidated ;  — 

3  eq.  ferrocyanide  /  3  eq.  ferrocyanogen ^^„^'  Prussian  blue. 

potassium  \  6  eq.  potassium 

2    eq.     nitrate    of  T  4  eq.  iron 

sesquioxide     of  ■<  6  eq.  oxygen 

iron  (  6  eq.  nitric  acid "^  6  eq.  nitrate   of   po- 

tassa. 

In  the  above  formula  no  account  is  taken  of  the  elements  of  water  which 
Prussian  blue  certainly  contains  ;  in  fact  it  must  be  looked  upon  as  still 
requiring  examination. 

The  theory  of  the  beautiful  test  of  Scheele  for  the  discovery  of  hydrocy- 
anic acid,  or  any  soluble  cyanide,  will  now  be  clearly  intelligible.  The 
liquid  is  mixed  with  a  salt  of  protoxide  of  iron  and  excess  of  caustic  alkali ; 
the  protoxide  of  iron  quickly  converts  the  alkaline  cyanide  into  ferrocy- 
anide. Ry  exposure  for  a  short  time  to  the  air,  another  portion  of  the 
hydrated  oxide  becomes  peroxidized ;  when  excess  of  acid  is  added,  this  is 
dissolved,  together  with  the  unaltered  protoxide  ;  and  thus  presented  to  the 
ferrocyanide  in  a  state  fitted  for  the  production  of  Prussian  blue. 

Basic  Prussian  Blue,  Fe4Cfy3-}-Fe203. —  This  is  a  combination  of  Prussian 
blue  with  sesquioxide  of  iron ;  it  is  formed  by  exposing  to  the  air  the  white 
or  pale  blue  precipitate  caused  by  a  ferrocyanide  in  a  solution  of  protosalt 
of  iron.  It  differs  from  the  preceding  in  being  soluble  in  pure  water, 
although  not  in  a  saline  solution. 

The  blue  precipitate  obtained  by  adding  nitrate  of  sesquioxide  of  ii"on  to 
a  large  excess  of  ferrocyanide  of  potassium,  is  a  mixture  of  insoluble 
Prussian  blue  with  a  compound  containing  that  substance  in  union  with  fer- 
rocyanide of  potassium,  or  Fe4Cfy3-f-2K2Cfy.  This  also  dissolves  in  water 
as  soon  as  the  salts  have  been  removed  by  washing. 


FERRICYANOGEN    AND    ITS    COMPOUNDS.         433 

The  other  ferrocyanides  may  be  despatched  in  a  few  words. 

The  soda-salt,  NagCfy--f-12H0,  crystallizes  in  yellow  four-sided  prisms, 
which  are  efflorescent  in  the  air  and  very  soluble. 

Ferrocyanide  of  ammonium,  (NH4)C2fy-f-3HO,  is  isomorphous  with  ferro- 
cyanide  of  potassium ;  it  is  easily  soluble,  and  is  decomposed  by  ebullition. 
Ferrocyanide  of  barium,  BagCfy,  prepared  by  double  decomposition,  or  by 
boiling  Prussian  blue  in  baryta-water,  forms  minute  yellow,  anhydrous  crys- 
tals, which  have  but  a  small  degree  of  solubility  even  in  boiling  water.  The 
corresponding  compounds  of  strontium,  calcium,  and  magnesium,  are  more 
freely  soluble.  The  ferrocyanides  of  silver,  lead,  zinc,  manganese,  and  bis- 
muth are  white  and  insoluble ;  those  of  nickel  and  cobalt  are  pale  green,  and 
insoluble ;  and,  lastly,  that  of  copper  has  a  beautiful  reddish-brown  tint. 

Ferrocyanides  with  two  basic  metals  are  occasionally  met  with  ;  when,  for 
example,  concentrated  solutions  of  chloride  of  calcium  and  ferrocyanide  of 
potassium  are  mixed,  a  sparingly-soluble  crystalline  precipitate  falls,  con- 
taining KCaCfy,  the  salt-radical  being  half  saturated  with  potassium,  and 
half  with  calcium ;  many  similar  compounds  have  been  formed. 

Ferri-,  or  ferridcyanogen,  CigNgFeg ;  or  Cfdy.  —  This  name  is  given  to 
a  substance,  by  some  thought  to  be  a  new  salt-radical,  isomeric  with  ferro- 
cyanogen,  but  differing  in  capacity  of  saturation  ;  it  has  never  been  isolated. 
Ferricyanide  of  potassium  is  thus  prepared: — Chlorine  is  slowly  passed,  with 
agitation,  into  a  somewhat  dilute  and  cold  solution  of  ferrocyanide  of  potas- 
sium, until  the  liquid  acquires  a  deep  reddish-green  colour,  and  ceases  to 
precipitate  a  salt  of  the  sesquioxide  of  iron.  It  is  then  evaporated  until  a 
skin  begins  to  form  upon  the  surface,  filtered,  and  left  to  cool ;  the  salt  ia 
pm-ified  by  re-crystallization.  It  forms  regular  prismatic,  or  sometimes 
tabular  crystals,  of  a  beautiful  ruby-red  tint,  permanent  in  the  air,  and  solu- 
ble in  4  parts  of  cold  water ;  the  solution  has  a  dark  greenish  colour.  The 
crystals  burn  when  introduced  into  the  flame  of  a  candle,  and  emit  sparks. 

Ferricyanide  of  potassium  contains  KgCfdy ;  hence  the  radical  is  tribasic ; 
the  salt  is  formed  by  the  abstraction  of  an  equivalent  of  potassium  from  2 
eq.  of  the  yellow  ferrocyanide  of  potassium.  It  is  decomposed  by  excess 
of  chlorine,  and  by  deoxidizing  agents,  as  sulphuretted  hydrogen.  The 
term  red  prussiaie  of  potash  is  often,  but  very  improperly,  given  to  this  sub- 
stance. 

Ferricyanide  of  hydrogen  is  obtained  in  the  form  of  a  reddish-brown  acid 
liquid,  by  decomposing  ferricyanide  of  lead  with  sulphuric  acid ;  it  is  very 
instable,  and  is  resolved,  by  boiling,  into  a  hydrated  sesquicyanide  of  iron, 
an  insoluble  dark  green  powder,  containing  FcjCyg-f-SHO,  and  hydrocyanic 
acid.  The  ferricyanides  of  sodium,  ammonium,  and  of  the  alkaline  earths, 
are  soluble ;  those  of  most  of  the.  other  metals  are  insoluble.  Ferricyanide 
of  potassium,  added  to  a  salt  of  the  sesquioxide  of  iron,  occasions  no  precipi- 
tate, but  merely  a  darkening  of  the  reddish-brown  colour  of  the  solution ; 
with  protoxide  of  iron,  on  the  other  hand,  it  gives  a  deep  blue  precipitate, 
containing"  FejCfdy,  which,  when  dry,  has  a  brighter  tint  than  that  of  Prus- 
sian blue ;  it  is  known  under  the  name  of  TurnbuU's  blue.  Hence,  ferri- 
cyanide of  potassium  is  as  excellent  a  test  for  protoxide  of  iron,  as  the  yellow 
ferrocyanide  is  for  the  sesquioxide. 

CoBALTOCYANOGEN.  — A  series  of  compounds  analogous  to  the  preceding, 
containing  cobalt  in  place  of  iron,  have  been  formed  and  studied ;  a  hydro- 
gen-acid has  been  obtained  and  a  number  of  salts,  which  much  resemble 
those  of  ferricyanogen.  Several  other  metals  of  the  same  isomorphous 
family  are  found  capable  of  replacing  iron  in  these  circumstances. 

Nttroprussides. — The  action  of  nitric  acid  upon  ferrocyanides  and  fern- 
cyanides  gives  rise  to  the  formation  of  a  very  interesting  series  of  new  salt::*, 
which  were  discovered  by  Dr.  Playfair.  The  general  formula  of  these  saltd 
37 


434  SULPHOCYANOGEN,     ITS    COMPOUNDS. 

appears  to  be  MjFejCygNO,  which  exhibits  a  close  relation  with  th(«e  of  the 
ferro-  and  ferricjanides. 

2M2Cfy     =     M4     Fej    Cy^     =     ferrocyanides. 
Mj     Fog     Cyg     =     ferricyanides. 

Mg    Fcj  <  ^^    =s     nitroprussides. 

According  to  this  formula,  the  formation  of  the  nitroprusside  would  con- 
sist in  the  reduction  of  the  nitric  acid  to  the  state  of  protoxide  of  nitrogen, 
which  replaces  1  eq.  of  cyanogen  in  2  eq.  of  ferrocyanide.  The  formation 
of  these  salts  is  attended  by  the  production  of  a  variety  of  secondary  pro- 
ducts, such  as  cyanogen,  oxamide,  hydrocyanic  acid,  nitrogen,  carbonic  acid, 
&c.  One  of  the  finest  compounds  of  this  series  is  the  nitroprusside  of 
sodium,  Nag.FeCygNO-f-^HO,  which  is  readily  obtained  by  treating  2  parts 
of  the  powdered  ferrocyanide  with  5  parts  of  common  nitric  acid,  previously 
diluted  with  its  own  volume  of  water.  The  solution,  after  the  evolution  of 
gas  has  ceased,  is  digested  on  the  water-bath,  until  salts  of  protoxide  of  iron 
no  longer  yield  a  blue  but  a  slate-coloured  precipitate.  The  liquid  is  now 
allowed  to  cool,  when  much  nitrate  of  potassa,  and  occasionally  oxamide,  is 
deposited ;  it  is  filtered  and  neutralized  with  carbonate  of  soda,  which  yields 
a  green  or  brown  precipitate,  and  furnishes  a  ruby-coloured  filtrate.  This, 
on  evaporation,  gives  a  crystallization  of  nitrate  of  potassa  and  soda,  toge- 
ther with  the  new  salt.  The  crystals  of  the  latter  are  selected  and  purified 
by  crystallization ;  they  are  rhombic,  and  of  a  splendid  ruby  colour.  The 
soluble  nitroprussides  strike  a  most  beautiful  violet  tint  with  soluble  sul- 
phides. This  reaction  is  recommended  by  Dr.  Plavfair  as  the  most  delicate 
test  for  alkaline  sulphides. 

SULPHOCYANOGEN,    ITS    COMPOUNDS   AND   DERIVATIVES. 

The  elements  of  cyanogen  combine  with  sulphur,  forming  a  very  important 
and  well-defined  salt-radical,  called  sulphocyanogetiy  which  contains  C2NS2, 
and  is  monobasic  ;  it  is  expressed  by  the  symbol  Csy. 

SuLPHOCYANiDE  OF  POTASSIUM,  KCsy.  —  Yellow  ferrocyanide  of  potassium, 
deprived  of  its  water  of  crystallization,  is  intimately  mixed  with  half  its 
weight  of  sulphur,  and  the  whole  heated  to  tranquil  fusion  in  an  iron  pot, 
and  kept  some  time  in  that  condition.  When  cold,  the  melted  mass  is  boiled 
with  water,  which  dissolves  out  a  mixture  of  sulphocyanide  of  potassium  and 
Bulphocyanide  of  iron,  leaving  little  behind  but  the  excess  of  sulphur  em- 
ployed in  the  experiment.  This  solution,  which  becomes  red  on  exposure  to 
the  air  from  the  oxidation  of  the  iron,  is  mixed  with  carbonate  of  potassa,  by 
which  the  oxide  of  iron  is  precipitated,  and  potassium  substituted ;  an  excess 
of  the  carbonate  must  be,  as  far  as  possible,  avoided.  The  filtered  liquid  is 
concentrated,  by  evaporation  over  an  open  fire,  to  a  small  bulk,  and  left  to 
cool  and  crystallize.  The  crystals  are  drained,  purified  by  re-solution,  if 
necessary,  or  dried  by  inclosing  them,  spread  on  filter-paper,  over  a  surface 
of  oil  of  vitriol,  covered  by  a  bell-jar. 

The  reaction  between  the  sulphur  and  the  elements  of  the  yellow  salt  is 
easily  explained  :  1  eq.  of  ferrocyanide  of  potassium,  and  G  eq.  sulphur, 
yielded  2  eq.  of  sulphocyanide  of  potassium,  and  1  eq.  of  sulphocyanide  of 
iron. 

KgCfy =CeN3Fe,K2-J-  6S=2(KC2NS2)-f  FeCaNSg. 

Anothe*  and  perhaps  simpler  process  consists  in  gradually  heating  to  low 
redness  in  a  covered  vessel  a  mixture  of  46  parts  of  dried  ferrocyanide  of 


SULPHOC  YANOGEN,    ITS    COMPOUNDS.  435 

potassium,  32  of  sulphur,  and  17  of  pure  carbonate  of  potassa.  The  mass  is 
exhausted  by  water,  the  aqueous  solution  evaporated  to  dryness  and  ex- 
tracted with  alcohoL  The  alcoholic  liquid  deposits  splendid  crystals  on  cool- 
ing or  evaporation. 

The  new  salt  crystallizes  in  long,  slender,  colourless  prisms,  or  plates, 
which  are  anhydrous  ;  it  has  a  bitter,  saline  taste,  and  is  destitute  of  poi- 
sonous properties ;  it  is  very  soluble  in  water  and  alcohol,  and  deliquesces 
when  exposed  to  a  moist  atmosphere.  When  heated,  it  fuses  to  a  colourless 
liquid,  at  a  temperature  far  below  that  of  ignition. 

When  chlorine  is  passed  into  a  strong  solution  of  sulphocyanide  of  potas- 
sium, a  large  quantity  of  a  bulky,  deep  yellow,  insoluble  substance,  resem- 
bling some  varieties  of  chromate  of  lead,  is  produced,  together  with  chloride 
of  potassium,  which  tends  to  choke  up  the  tube  delivering  the  gas ;  the  liquid 
sometimes  assumes  a  deep  red  tint,  and  disengages  a  pungent  vapour,  pro- 
bably chloride  of  cyanogen.  This  yellow  matter  may  be  collected  on  a  filter, 
well  washed  with  boiling  water,  and  dried :  it  retains  its  brilliancy  of  tint. 
The  term  sulphocyanogen  has  generally  been  applied  to  this  substance,  from 
its  supposed  identity  with  the  radical  of  the  sulphocyanides ;  it  is,  however, 
invariably  found  to  contain  both  oxygen  and  hydrogen,  and  a  formula  much 
more  complex  than  that  belonging  to  the  true  sulphocyanogen,  namely  CgHj 
N4SgO,  has  been  lately  assigned  to  it.  The  yellow  substance  is  quite  insoluble 
in  water,  alcohol,  and  ether;  it  dissolves  in  concentrated  sulphuric  acid, 
from  which  it  is  precipitated  by  dilution.  Caustic  potassa  also  dissolves  it, 
with  decomposition;  acids  throw  down  from  this  solution  a  pale  yellow, 
insoluble  body,  having  acid  properties.  When  heated  in  a  dry  state,  the 
so-called  sulphocyanogen  evolves  sulphur  and  bisulphide  of  carbon,  and 
leaves  a  curious,  pale  straw-yellow  substance,  called  mellon,  which  coniains 
CgN^,  and  is  known  to  combine  with  hydrogen  and  the  metals.  Mellon  bears 
a  dull  red-heat  without  decomposition,  but  is  resolved  by  strong  ignition  inta 
a  mixture  of  cyanogen  and  nitrogen  gases.  It  is  quite  insoluble  in  water^ 
alcohol,  and  dilute  acids. 

Hydrosulphocvanic  acid,  HCsy,  is  obtained  by  decomposing  sulphocya- 
nide of  lead,  suspended  in  water,  by  sulphuretted  hydrogen.  The  filtered 
solution  is  colourless,  very  acid,  and  not  poisonous ;  it  is  easily  decomposed, 
in  a  very  complex  manner,  by  ebullition ;  and  by  exposure  to  the  air.  By 
neutralizing  the  liquid  with  ammonia,  and  evaporating  very  gently,  to  dry- 
ness, sulphocyanide  of  ammonium,  NH4Csy,  is  obtained  as  a  deliquescent, 
saline  mass.  This  salt  may  be  conveniently  prepared  by  digesting  hydro- 
cyanic acid  with  yellow  sulphide  of  ammonium,  and  boiling  oif  the  excess  of 
the  latter  (NH^Sj-f-HCyrrsNH^Csy-f-HS).  The  sulphocyanides  of  ^ocfmm, 
barium,  strontium,  calcium,  manganese,  and  iron  are  colourless,  and  very 
soluble  ;  those  of  lead  and  silver  are  white  and  insoluble.  A  soluble  sulpho- 
cyanide, mixed  with  a  salt  of  the  sesquioxide  of  iron,  gives  no  precipitate 
but  causes  the  liquid  to  assume  a  deep  blood-red  tint,  exactly  similar  to  that 
caused  under  similar  circumstances  by  meconic  acid ;  hence  the  occasional 
use  of  sulphocyanide  of  potassium  as  a  test  for  iron  in  the  state  of  sesqui- 
oxide. The  great  facility  with  which  hydrocyanic  acid  may  be  converted 
into  sulphocyanide  of  ammonium  enables  us  to  ascertain  the  presence  by  the 
iron-test  just  described.  The  cyanide  to  be  examined  is  mixed  in  a  watch- 
glass  with  some  hydrochloric  acid  and  covered  with  another  watch-glass,  to 
which  a  few  drops  of  yellow  sulphide  of  ammonium  adhere.  On  heating  thv 
mixture,  hydrocyanic  acid  is  disengaged,  which  combines  with  the  sulphide 
of  ammonium,  and  produces  sulphocyanide  of  ammonium ;  this,  after  the 
expulsion  of  the  excess  of  sulphide,  yields  the  red  colour  with  solution  of 
sesquioxide  of  iron. 

Selbnocyanoqen. — A  series  of  salts  containing  selenium,  and  corresponding 


h 


436      UREA;   URIC  acid   and  its   products. 

in  their  composition  and  properties  with  sulphocyanides,  exist.  They  have 
been  lately  studied  by  Mr.  Crookcs. 

Melam.  —  Such  is  the  name  given  by  Liebig  to  a  curious  buflf-coloured, 
insoluble,  amorphous  substance,  obtained  by  the  distillation  at  a  high  tem- 
perature of  sulphocyanide  of  ammonium.  It  may  be  prepared  in  large 
quantity  by  intimately  mixing  1  part  of  perfectly  dry  sulphocyanide  of  po- 
tassium with  2  parts  of  powdered  sal-ammoniac,  and  heating  the  mixture 
for  some  time  in  a  retort  or  flask ;  bisulphide  of  carbon,  sulphide  of  ammo- 
nium, and  sulphuretted  hydrogen  are  disengaged  and  volatilized,  while  a 
mixture  of  melam,  chloride  of  potassium,  and  some  sal-ammoniac  remains ; 
the  two  latter  substances  are  removed  by  washing  with  hot  water.  Melam 
contains  Cj^HgNjj ;  it  dissolves  in  concentrated  sulphuric  acid,  and  gives,  by 
dilution  with  water  and  long  boiling,  cyanuric  acid.  The  same  substance  is 
produced  with  disengagement  of  ammonia  when  melam  is  fused  with  hydrate 
of  potassa.  When  strongly  heated,  melam  is  resolved  into  mellon  and 
ammonia. 

If  melam  be  boiled  for  a  long  time  in -a  moderately  strong  solution  of 
caustic  potassa,  until  the  whole  has  dissolved,  and  the  liquid  be  then  concen 
trated,  a  crystalline  substance  separates  on  cooling,  which  is  called  melamine, 
By  re-crystallization  it  is  obtained  in  colourless  crystals,  having  the  figure 
of  an  octahedron  with  rhombic  base ;  it  is  but  slightly  soluble  in  cold  water, 
fusible  by  heat,  and  volatile  with  trifling  decomposition.  It  contains  CgHgNc 
and  acts  as  a  base,  combining  with  acids  to  crystallizable  compounds.  A 
second  basic  substance  called  ammeline,  very  similar  in  properties  to  mela- 
mine,  is  found  in  the  alkaline  mother-liquor  from  which  the  melamine  has 
separated ;  it  is  thrown  down  on  neutralizing  the  liquid  with  acetic  acid. 
The  precipitate,  dissolved  in  dilute  nitric  acid,  yields  crystals  of  nitrate  of 
ammeline,  from  which  the  pure  ammeline  may  be  separated  by  ammonia.  It 
forms  a  brilliant  white  powder  of  minute  needles,  insoluble  in  water  and 
alcohol,  and  contains  CgHjNgOj.  When  ammeline  is  dissolved  in  concentrated 
sulphuric  acid,  and  the  solution  mixed  with  a  large  quantity  of  water,  or, 
better,  spirit  of  wine,  a  white,  insoluble  powder  falls.  Which  is  designated 
ammelide,  and  is  found  to  contain  C,2HgN90g.  When  long  boiled  with  dilute 
sulphuric  acid,  melamine,  ammeline,  and  ammelide  are  converted  into  cya- 
nuric acid  and  ammonia. 

UREA  ;    UEIC   ACID    AND   ITS   PRODUCTS. 

These  bodies  are  closely  connected  with  the  cyanogen-compounds,  and  may 
be  most  conveniently  discussed  in  the  present  place. 

Urea.  —  Urea  may  be  extracted  from  its  natural  source,  the  urine,  or  it 
may  be  prepared  by  artificial  means.  Fresh  urine  is  concentrated  in  a 
water-bath,  until  reduced  to  an  eighth  or  a  tenth  of  its  original  volume,  and 
filtered  through  cloth  from  the  insoluble  deposit  of  urates  and  phosphates. 
The  liquid  is  mixed  with  about  an  equal  quantity  of  a  strong  solution  of 
oxalic  acid  in  hot  water,  and  the  whole  vigorously  agitated  and  left  to  cool. 
A  very  copious  fawn-coloured  crystalline  precipitate  of  oxalate  of  urea  is 
obtained,  which  may  be  placed  upon  a  cloth  filter,  slightly  washed  with  cold 
water,  and  pressed.  This  is  to  be  dissolved  in  boiling-hot  water,  and  pow- 
dered chalk  added  until  efi"ervescence  ceases,  and  the  liquid  becomes  neutral. 
The  solution  of  urea  is  filtered  from  the  insoluble  oxalate  of  lime,  warmed 
with  a  little  animal  charcoal,  again  filtered,  and  concentrated  by  evaporation, 
avoiding  ebullition,  until  crystals  form  on  cooling;  these  are  purified  by  a 
repetition  of  the  last  part  of  the  process.  Urea  can  be  extracted  in  great 
abundance  from  the  urine  of  horses  and  cattle,  duly  concentrated,  and  from 
which  the  hippuric  acid  has  been  separated  by  the  addition  of  hydrochloric 
acid ;  oxalic  acid  then  throws  down  the  oxalate  in  such  quantity  as  to  render 


urea;    uric  acid  and   its   products.       437 

the  whole  semi-solid.  Another  process  consists  in  precipitating  the  evapo- 
rated urine  with  concentrated  nitric  acid,  when  nitrate  of  urea  is  precipitated, 
which  is  re-crystallized  with  animal  charcoal,  and  lastly  decomposed  by  car- 
bonate of  baryta.  A  mixture  of  nitrate  of  baryta  and  urea  is  formed,  which 
is  evaporated  to  dryness  on  the  water-bath,  and  exhausted  with  alcohol,  from 
which  the  urea  crystallizes  on  cooling. 

By  artificial  means,  urea  is  produced  by  heating  solution  of  cyanate  of 
ammonia.  The  following  method  of  proceeding  yields  it  in  any  quantity 
that  can  be  desired.  Cyanate  of  potassa,  prepared  by  Liebig's  process,'  is 
dissolved  in  a  small  quantity  of  water,  and  a  quantity  of  dry  neutral  sulphate 
of  ammonia,  equal  in  weight  to  the  cyanate,  added.  The  whole  is  evapo- 
rated to  dryness  in  a  water-bath,  and  the  dry  residue  boiled  with  strong 
alcohol,  which  dissolves  out  the  urea,  leaving  the  sulphate  of  potassa  and 
the  excess  of  sulphate  of  ammonia  untouched.  The  filtered  solution,  con- 
centrated by  distilling  oflF  a  portion  of  the  spirit,  deposits  the  urea  in  beau- 
tiful crystals  of  considerable  magnitude. 

Urea  forms  transparent,  colourless,  four-sided  prisms,  which  are  soluble 
in  an  equal  weight  of  cold  water,  and  in  a  much  smaller  quantity  at  a  high 
temperature.  It  is  also  readily  dissolved  by  alcohol.  It  is  inodorous,  has 
a  cooling,  saline  taste,  and  is  permanent  in  the  air,  unless  the  latter  be  very 
damp.  When  heated,  it  melts,  and  at  a  higher  temperature,  decomposes  with 
evolution  of  ammonia  and  cyanate  of  ammonia ;  cyanuric  acid  remains,  which 
bears  a  much  greater  heat  without  change.  The  solution  of  urea  is  neutral 
to  test-paper ;  it  is  not  decomposed  in  the  cold  by  alkalis  or  by  hydrate  of 
lime,  but  at  a  boiling  heat  emits  ammonia,  and  forms  a  carbonate  of  the 
base.  The  same  change  happens  by  fusion  with  the  alkaline  hydrates. 
Brought  into  contact  with  nitrous  acid,  it  is  decomposed  instantly  into  a 
mixture  of  nitrogen  and  carbonic  acid  gases ;  this  decomposition  explains 
the  use  of  urea  in  preparing  nitric  ether  (see  page  354).  With  chlorine  it 
yields  hydrochloric  acid,  nitrogen,  and  carbonic  acid.  Crystallized  urea  is 
anhydrous;  it  contains  C2n4N202,  or  the  elements  of  cyanate  of  oxide  of  ammo- 
nium. It  differs  from  carbonate  of  ammonia  by  the  elements  of  water ;  hence 
it  might  with  some  propriety  be  called  carbamide.  It  is  easily  converted  into 
carbonate  of  ammonia  by  assimilating  the  oxygen  and  hydrogen  of  2  eq.  of 
water.  A  solution  of  pure  urea  shows  no  tendency  to  change  by  keeping, 
and  is  not  decomposed  by  boiling ;  in  the  urine,  on  the  other  hand,  where 
it  is  associated  with  putrctiable  organic  matter,  as  mucus,  the  case  is  ditfe- 
rent.  In  putrid  urine  no  urea  can  be  found,  but  enough  carbonate  of 
ammonia  to  cause  brisk  eifervescence  with  an  acid ;  and  if  urine,  in  a  recent 
state,  be  long  boiled,  it  gives  off  ammonia  and  carbonic  acid  from  the  same 
source. 

Urea  acts  as  a  salt-base ;  with  nitric  acid  it  forms  a  sparingly  soluble 
compound,  which  crystallizes,  when  pure,  in  small,  indistinct,  colourless 
plates,  containing  single  equivalents  of  urea,  nitric  acid,  and  water.  When 
colourless  nitric  acid  is  added  to  urine,  concentrated  to  a  fourth  or  a  sixth 
of  its  volume,  and  cold,  the  nitrate  crystallizes  out  in  large,  brilliant,  yellow 
laminae,  which  are  very  insoluble  in  the  acid  liquid.  The  production  of 
this  nitrate  is  highly  characteristic  of  urea.  The  oxalate,  when  pure,  crys- 
tallizes in  large,  ti-ansparent,  colourless  plates,  which  have  an  acid  reaction, 
and  are  sparingly  soluble ;  it  contains  an  equivalent  of  water.  Urea  forma 
several  compounds  with  metallic  salts,  e.  g.,  with  those  of  mercury.  On 
mixing  a  liquid  containing  urea  with  a  solution  of  nitrate  of  protoxide  of 
mercury,  a  white  precipitate  takes  place,  which  is  a  compound  of  urea  with 
4  eq.  of  protoxide  of  mercury.     If  the  nitric  acid  which  is  thus  set  free,  be 

»  See  page  427. 
o7* 


488  URIC    ACID    AND    ITS    PRODUCTS. 

neutralized  by  the  addition  of  an  alkali  or  baryta-water,  the  whole  of  the 
urea  is  removed  from  the  liquid  in  the  form  of  tlie  above  compounds.  Prof. 
Liebig,  to  whom  we  are  indebted  for  this  observation,  has  based  upon  this 
deportment  a  process  of  determining  the  amount  of  urea  in  urine.  The  de- 
tails of  this  method,  which  is  equally  interesting  to  the  chemist  and  the 
physiologist,  have  not  yet  been  published. 

A  series  of  substances  analogous  to  urea,  which  have  lately  been  disco- 
vered and  described  under  the  name  of  methylamine-urea,  ethylamine-urea, 
biethylamine-urea,  &c.,  will  be  noticed  in  the  section  on  the  vegeto-alkalis. 

Uric,  or  lithic  acid. — This  is  a  product  of  the  animal  organism,  and  has 
never  been  formed  by  artificial  means.  It  may  be  prepared  from  human 
urine  by  concentration,  and  addition  of  hydrochloric  acid ;  it  crystallizes 
out  after  some  time  in  the  form  of  small,  reddish,  translucent  grains,  very 
difficult  to  purify.  A  much  preferable  method  is,  to  employ  the  solid  white 
excrement  of  serpents,  which  can  be  easily  procured ;  this  consists  almost 
entirely  of  uric  acid  and  urate  of  ammonia.  It  is  reduced  to  powder,  and 
boiled  in  dilute  solution  of  caustic  potassa ;  the  liquid,  filtered  from  the  in- 
significant residue  of  feculent  matter,  and  earthy  phosphates,  is  mixed  with 
excess  of  hydrochloric  acid,  boiled  for  a  few  minutes,  and  left  to  cool.  The 
product  is  collected  on  a  filter,  washed  until  free  from  chloride  of  potassium, 
and  dried  by  gentle  heat. 

Uric  acid,  thus  obtained,  forms  a  glistening,  snow-white  powder,  tasteless, 
inodorous,  and  very  sparingly  soluble.  It  is  seen 
Fig.  173.  under  the  microscope  to    consist  of  minute,  but 

regular  crystals  (fig.  173).  It  dissolves  in  concen- 
/Oy  ^^&  trated  sulphuric  acid  without  apparent  decomposi- 

t->'c^^X^  tion,  and  is  precipitated  by  dilution  with  water. 

By  destructive  distillation,  uric  acid  yields  cyanic, 
hydrocyanic,  and  carbonic  acids,  carbonate  of  am- 
monia, and  a  black  coaly  residue,  rich  in  nitrogen. 
C^/A  '^^^&  ^      I^y  fusion  with  hydrate  of  potassa,  it  furnishes 

^  \-J  B  C^*^  carbonate  and  cyanate  of  the  base,  and  cyanide  of 

"^^^[[fil  j~-N  ^25  the  alkaline  metal.  When  treated  with  nitric  acid 
^^    wJ  Q  and  with  binoxide  of  lead,  it  undergoes  decomposi- 

tion in  a  manner  to  be  presently  described. 

Uric  acid  is  found  by  analysis  to  contain  C,oH2N^04,2HO.  It  is  a  bibasic 
acid. 

The  only  salts  of  uric  acid  that  have  attracted  any  attention  are  those  of 
the  alkalis;  acid  urate  of  potassa  contains  KO,HO,C,oH2N404;  it  is  deposited 
from  a  hot,  saturated  solution  of  uric  acid  in  the  dilute  alkali  as  a  white, 
sparingly  soluble  concrete  mass,  composed  of  minute  needles  ;  it  requires 
about  500  parts  of  cold  water  for  solution,  is  rather  more  soluble  at  a  high 
temperature,  and  much  more  soluble  in  excess  of  alkali.  Urate  of  soda  re- 
sembles the  salt  of  potassa ;  it  forms  the  chief  constituent  of  the  gouty  con- 
cretions in  the  joints,  called  chalk-stones.  Urate  of  ammonia  is  also  a  sparingly 
soluble  compound,  requiring  for  the  purpose  about  1000  parts  of  cold  water ; 
the  solubility  is  very  much  increased  by  the  presence  of  a  small  quantity  of 
certain  salts,  as  chloride  of  sodium.  This  is  the  most  common  of  the  urinary 
deposits,  forming  a  buflf-coloured  or  pinkish  cloud  or  muddiness,  which  dis- 
appears by  re-solution  when  the  urine  is  warmed ;  the  secretion  from  which 
this  is  deposited  has  an  acid  reaction.     It  occurs  also  as  a  calculus. 

The  following  substances  result  from  the  oxidation  of  uric  acid  by  binoxide 
of  lead  and  nitric  acid ;  they  are  some  of  the  most  beautiful  and  interesting 
bodies  known,  most  of  which  have  been  discovered  by  Liebig  and  Wohler. 

Allantoin.  — Allantoin  occurs  ready  formed  in  the  allantoic  liquid  of  the 
f'Xtal  calf.     It  is  produced  artificially  by  boiling  together  water,  uric  acid, 


URIC    ACID    AND    ITS    PRODUCTS.  4S9 

and  pure,  freshly  prepared  binoxide  of  lead  ;  the  filtered  liquid,  duly  concen- 
trated by  evaporation,  deposits  crystals  of  allantoin  on  cooling,  which  are 
purified  by  re-solution  and  the  use  of  animal  charcoal.  It  forms  small  but 
most  brilliant  prismatic  crystals,  which  are  transparent  and  colourless,  des- 
titute of  taste,  and  without  action  on  vegetable  colours.  Allantoin  dissolves 
in  1 60  parts  of  cold  water,  and  in  a  small  quantity  at  the  boiling  temperature. 
It  is  decomposed  by  boiling  with  nitric  acid,  and  by  oil  of  vitriol  when  con- 
centrated and  hot,  being  in  this  case  resolved  into  ammonia,  carbonic  acid, 
and  carbonic  oxide.  Heated  with  concentrated  solution  of  caustic  alkalis,  it 
is  decomposed  into  ammonia  and  oxalic  acid,  which  latter  combines  with  the 
base.  These  reactions  are  explained  by  the  analysis  of  the  substance,  which 
shows  it  to  be  composed  of  the  elements  of  oxalate  of  ammonia  minus  those 
of  three  equivalents  of  water,  or  C4H3N2O3. 

The  production  of  allantoin  from  uric  acid  and  binoxide  of  lead  is  also  per- 
fectly intelligible ;  1  eq.  of  uric  ncid,  2  eq.  of  oxygen  from  the  binoxide,  and 
3  eq.  of  water,  contain  the  elements  of  allantoin,  2  eq.  of  oxalic  acid,  and  1 
eq.  of  urea. 

C10H4N4O6+2OX  _  f  C^HgN.Oa-f  2(H0,C,03) 
-f  3H0  /  "^  I       -f-CgH^NjOj. 

The  insoluble  matter  from  which  the  solution  of  allantoin  is  filtered  con- 
sists in  great  part  of  oxalate  of  lead,  and  the  mother-liquor  from  wliich  the 
crystals  of  allantoin  have  separated,  yields,  on  farther  evaporation,  a  large 
quantity  of  pure  urea. 

Alloxan.  —  This  is  the  characteristic  product  of  the  action  of  concentrated 
nitric  acid  on  uric  acid  in  the  cold.  An  acid  is  prepared,  of  sp.  gr.  1-45,  or 
thereabouts,  and  placed  in  a  shallow  open  basin ;  into  this  a  third  of  its 
weight  of  dry  uric  acid  is  thrown,  by  small  portions,  with  constant  agitation, 
care  being  taken  that  the  temperature  never  rises  to  any  considerable  extent. 
The  uric  acid  at  first  dissolves  with  copious  eifervescence  of  carbonic  acid 
and  nitrogen,  and  eventually,  the  whole  becomes  a  mass  of  white,  crystal- 
line, pasty  matter.  This  is  left  to  stand  some  hours,  drained  from  the  acid 
liquid  in  a  funnel  whose  neck  is  stopped  with  powder  and  fragments  of  glass, 
and  afterwards  more  effectually  dried  upon  a  porous  tile.  This  is  alloxan  in 
a  crude  state ;  it  is  purified  by  solution  in  a  small  quantity  of  water,  and 
crystallization. 

Alloxan  crystallizes  with  facility  from  a  hot  and  concentrated  solution, 
slowly  suffered  to  cool,  in  solid,  hard,  anhydrous  crystals  of  great  regularity, 
which  are  transparent,  nearly  colourless,  have  a  high  lustre,  and  the  figure 
of  a  modified  rhombic  octahedron,  A  cold  solution,  on  the  other  hand,  left 
to  evaporate  spontaneously,  deposits  large  foliated  crystals,  which  contain  6 
eq.  of  water ;  they  efl[loresce  rapidly  in  the  air.  Alloxan  is  very  soluble  in 
water  ;  the  solution  has  an  acid  reaction,  a  disagreeable  astringent  taste,  and 
stains  the  skin,  after  a  time,  red  or  purple.  It  is  decomposed  by  alkalis,  and 
both  by  oxidizing  and  de-oxidizing  agents  ;  its  most  characteristic  property 
is  that  of  forming  a  deep  blue  compound  with  a  salt  of  protoxide  of  iron  and 
an  alkali. 

Alloxan  contains  Cgll^NjOig ;  its  production  is  thus  illustrated :  1  eq.  of 
uric  acid,  4  eq.  of  water,  and  2  eq.  of  nitric  acid,  contain  the  elements  of 
alloxan,  2  eq.  carbonic  acid,  2  eq.  of  free  nitrogen,  1  eq.  of  nitrate  of  am- 
pionia: — 

^ +2JhO,NO^'^  }  =CsH,N30,o-f  2C0,+N,-f  NH,0,NO,. 

When  to  a  solution  of  alloxan,  heated  to  140°  (60°C),  baryta-water  is  added 
as  long  as  the  precipitate  first  produced  re-dissolves,  and  the  filtered  solutiot. 


440  URIC    ACID    AND    ITS    PRODUCTS. 

is  then  left  to  cool,  a  substance  is  deposited  in  small,  colourless,  pearly  crys- 
tals, which  consists  of  baryta  in  combination  with  a  new  acid,  the  alloxanic. 
From  this  salt  the  base  may  be  separated  by  the  cautious  addition  of  dilute 
sulphuric,  acid :  the  filtered  liquid  by  gentle  evaporation  yields  alloxanic  acid 
in  small  radiated  needles.  It  has  an  acid  taste  and  reaction,  decomposes  car- 
bonates, and  dissolves  zinc  with  disengagement  of  hydrogen.  It  is  a  bibasic 
acid,  and  contains  in  the  hydrated  state  CgH2N20g,2HO  ;  hence  it  is  isomeric 
with  alloxan.  The  alloxanates  of  the  alkalis  are  freely  soluble ;  those  of  the 
earths  dissolve  in  a  large  quantity  of  tepid  water^  and  that  of  silver  is  quite 
insoluble  and  anhydrous. 

If  a  warm  saturated  solution  of  alloxanate  of  baryta  is  heated  to  ebullition,. 
a  precipitate  falls,  which  is  a  mixture  of  carbonate  and  alloxanate  of  baryta 
with  an  insoluble  salt  of  a  second  new  acid,  the  mesoxalic ;  the  solution  is 
found  to  contain  unaltered  alloxanate  of  baryta  and  urea.  Mesoxalic  acid 
is  best  prepared  by  slowly  adding  solution  of  alloxan  to  a  boiling-hot  solution 
of  acetate  of  lead ;  the  heavy  granular  precipitate  of  mesoxalate  of  lead  thus 
produced  is  washed  and  decomposed  by  sulphuretted  hydrogen  ;  urea  is  also 
formed  in  this  experiment.  Hydrate  of  mesoxalic  acid  is  crystallizable  ;  it 
has  a  sour  taste  and  powerfully  acid  reaction,  and  resists  a  boiling  heat :  it 
forms  sparingly  soluble  salts  with  baryta  and  lime,  and  a  yellowish  insoluble 
compound  with  oxide  of  silver,  which  is  reduced  with  effervescence  when 
gently  heated.  This  remarkable  acid  contains  as  hydrate  €304,2110,  and  is 
consequently  bibasic ;  it  is  formed  by  the  resolution  of  alloxan  into  urea,  and 
2  eq.  of  mesoxalic  acid :  — 

C8H4N20,o+2IIO=C2H4NgOj+2(HO,C80^). 

When  ammonia  in  excess  is  added  to  a  solution  of  alloxan,  the  whole 
heated  to  ebullition,  and  afterwards  supersaturated  with  dilute  sulphuric 
acid,  a  yellow,  light  precipitate  falls,  which  increases  in  quantity  as  the  liquid 
cools.  This  is  mykomelinic  add;  it  is  but  feebly  soluble  in  water,  easily  dis- 
solved by  alkalis,  and  forms  a  yellow  compound  with  oxide  of  silver.  Myko- 
melinic acid  contains  C^H5N405 ;  it  is  produced  by  the  conversion  of  alloxan 
and  2  eq.  of  ammonia  into  1  eq.  of  mykomelinic  acid  and  5  eq.  of  water. 

Parabanic  Acid. — This  is  the  characteristic  product  of  the  action  of 
moderately  strong  nitric  acid  on  uric  acid  "or  alloxan,  by  the  aid  of  heat ;  it 
is  conveniently  prepared  by  heating  together  1  part  of  uric  acid  and  8  parts 
of  nitric  acid  until  the  reaction  has  nearly  ceased ;  the  liquid  is  evaporated 
to  a  syrupy  state,  and  left  to  cool ;  the  acid  is  drained  from  the  mother- 
liquid  and  purified  by  re-crystallization.  Parabanic  acid  forms  beautiful 
colourless,  transparent,  thin,  prismatic  crystals,  which  are  permanent  in  the 
air ;  it  is  easily  soluble  in  water,  has  a  pure  and  powerful  acid  taste,  and 
reddens  litmus  strongly.  Neutralized  with  animonia,  and  mixed  with  nitrate 
of  silver,  it  gives  a  white  precipitate.  Crystallized  parabanic  acid  contains 
^6^2^4'2H^  ;  its  production  is  thus  explained  :  1  eq.  of  uric  acid,  2  eq.  of 
water,  and  4  eq.  of  oxygen  from  the  nitric  acid,  yield  1  eq.  of  parabanic 
acid,  4  eq.  of  carbonic  acid,  and  2  eq.  of  ammonia  ;  or,  alloxan  and  four 
additional  equivalents  of  oxygen  furnish  1  eq.  of  parabanic  acid,  2  eq.  of 
carbonic  acid,  and  4  eq.  of  water. 

The  alkaline  parabanates  undergo  a  singular  change  by  exposure  to  heat ; 
if  a  solution  of  the  acid  be  saturated  with  ammonia,  boiled  for  a  moment, 
and  then  left  to  cool,  a  substance  separates  in  tufts  of  beautiful  colourless 
needles ;  this  is  the  ammonia-salt  of  an  acid  called  the  oxaluric.  The  hy- 
drated acid  is  procured  by  adding  an  excess  of  dilute  sulphuric  acid  to  a  hot 
and  strong  solution  of  oxaliirate  of  ammonia,  and  cooling  the  whole 
rapidly  It  forms  a  white,  crystalline  powder,  of  acid  taste  and  reaction, 
capable  of  combining  with  bases :  the  salts  of  baryta  and  lime  are  sparingly 


URIC    ACID    AND    ITS    PRODUCTS.  441 

soluble ;  that  of  silver  crystallizes  from  the  mixed  hot  solution  of  nitrate  of 
silver  and  oxalnrate  of  ammonia  in  long,  silky  needles.  Oxaluric  acid  ia 
composed  of  CeHgNjO^jHO;  or  the  elements  of  1  eq,  of  parabanic  acid  and 
3  eq.  of  water.  A  solution  of  oxaluric  acid  is  resolved  by  ebullition  into 
free  oxalic  acid  and  oxalate  of  urea. 

Thionuric  acid. — A  cold  solution  of  alloxan  is  mixed  veith  a  saturated 
solution  of  sulphurous  acid  in  water,  in  such  quantity  that  the  odour  of  the 
gas  remains  quite  distinct ;  an  excess  of  carbonate  of  ammonia  mixed  with 
a  little  caustic  ammonia  is  then  added,  and  the  whole  boiled  for  a  few 
minutes.  On  cooling,  thionurate  of  ammonia  is  deposited  in  great  abundance, 
forming  beautiful  colourless,  crystalline  plates,  which  by  solution  in  water 
and  re-crystallization  acquire  a  fine  pink  tint.  A  solution  of  this  salt  gives 
with  acetate  of  lead  a  precipitate  of  insoluble  thionurate  of  the  oxide  of 
that  metal,  which  is  at  first  white  and  gelatinous,  but  shortly  becomes  dense 
and  crystalline ;  from  this  compound  the  hydrated  acid  may  be  obtained  by 
the  aid  of  sulphuretted  hydrogen.  It  forms  a  white,  crystalline  mass,  per- 
manent in  the  air,  very  soluble  in  water,  of  acid  taste  and  reaction,  and 
capable  of  combining  directly  with  bases.  When  its  solution  is  heated  to 
the  boiling-point,  it  undergoes  decomposition,  yielding  sulphuric  acid  and  a 
very  peculiar  and  nearly  insoluble  substance,  called  uramile.  Thionuric  acid 
is  bibasic;  the  hydrate  contains  C8ll5N3S20,2,2HO ;  or  the  elements  of 
alloxan,  an  equivalent  of  ammonia,  and  2  eq.  of  sulphurous  acid. 

Uramile. — The  product  of  the  decomposition  by  heat  of  hydrated  thionu- 
ric acid.  Thionurate  of  ammonia  is  dissolved  in  hot  water,  mixed  with  a 
small  excess  of  hydrochloric  acid,  and  the  whole  boiled  in  a  flask ;  a  white, 
crystalline  substance  begins  in  a  few  moments  to  separate,  which  increases 
in  quantity  until  the  contents  of  the  vessel  often  become  semi-solid ;  this  is 
uramile.  After  cooling,  it  is  collected  on  a  filter,  washed  with  cold  water  to 
remove  the  sulphuric  acid,  and  dried  by  gentle  heat,  during  which  it  fre- 
quently becomes  pinkish.  Examined  by  a  lens,  it  is  seen  to  consist  of 
minute  acicular  crystals.  It  is  tasteless  and  nearly  insoluble  in  water,  but 
dissolves  in  ammonia  and  the  fixed  alkalis.  The  ammoniacal  solution  be- 
comes purple  in  the  air.  It  is  decomposed  by  strong  nitric  acid,  alloxan 
and  nitrate  of  ammonia  being  generated.  Uramile  contains  CgHgNgOg ;  or 
thionuric  acid  minus  the  elements  of  2  eq.  of  sulphuric  acid. 

Uramilic  acid. — When  a  cold  saturated  solution  of  thionurate  of  ammo- 
nia is  mixed  with  dilute  sulphuric  acid,  and  evaporated  in  a  water-bath, 
instead  of  uramile,  another  substance,  uramilic  acid,  is  formed  and  deposited 
in  slender,  colourless  prisms,  soluble  in  8  parts  of  cold  water.  Uramilic 
acid  dissolves  in  concentrated  sulphuric  acid  without  apparent  decomposi- 
tion ;  it  has  a  feeble  acid  taste  and  reaction,  and  combines  with  bases.  The 
salts  of  the  alkalis  are  easily  soluble ;  those  of  the  earths  much  less  so,  and 
that  of  the  oxide  of  silver  is  insoluble.  Uramilic  acid  contains  CjcHj^NgOiB ; 
2  eq.  of  uramile  and  3  eq.  of  water  contain  the  elements  of  uramilic  acid 
and  1  eq.  of  ammonia.     It  is  a  substance  difficult  of  preparation. 

Alloxantin. — This  is  the  chief  product  of  the  action  of  hot  dilute  nitrio 
acid  upon  uric  acid ;  the  surest  and  best  method  of  preparing  it,  however, 
is  by  passing  a  stream  of  sulphuretted-hydrogen  gas  through  a  moderately 
strong  and  cold  solution  of  alloxan.  The  impure  mother-liquid  from  which 
the  crystals  of  alloxan  have  separated  answers  the  purpose  perfectly  well* 
it  is  diluted  with  a  little  water,  and  a  copious  stream  of  gas  transmitted 
through  it.  Sulphur  is  deposited  in  large  quantity,  mixed  with  a  white, 
crystalline  substance,  which  is  the  alloxantin.  The  product  is  drained  upon 
a  filter,  slightly  washed,  and  then  boiled  in  water ;  the  filtered  solution 
deposits  the  alloxantin  on  cooling.  Alloxantin  forms  small,  four-sided, 
oblique  rhombic  prisms,  colourless  and  transparent ;  it  is  soluble  with  diffi- 
culty in  cold  water,  but  more  freely  at  a  boiling  temperature.     The  solution 


442  URIC    ACID    AND    ITS    PRODUCTS. 

reddens  litmus,  gives  with  baryta-water  a  violet-coloured  precipitate,  which 
disappears  on  heating,  and  when  mixed  with  nitrate  of  silver  produces  a 
black  precipitate  of  metallic  silver.  Heated  with  chlorine  or  nitric  acid,  it 
is  changed  by  oxidation  to  alloxan.  The  crystals  become  red  when  exposed 
to  ammoniacal  vapours.  Alloxan  tin  contains  CgHjNgOjo ;  or  alloxan  plus  1 
equivalent  of  hydrogen. 

This  substance  is  readily  decomposed ;  when  a  stream  of  sulphuretted 
hydrogen  is  passed  through  a  boiling  solution,  sulphur  is  deposited  and  an 
acid  liquid  produced,  supposed  to  contain  a  new  acid,  to  which  the  term 
dialuric  is  applied.  When  neutralized  by  ammonia  it  yields  a  salt  which 
crystallizes  in  colourless  silky  needles,  containing  NH40,C8N204  -j-  3H0 
They  become  deep  red  when  heated  to  212°  (100°C)  in  the  air.  A  hot  satu- 
rated  solution  of  alloxantin  mixed  with  a  neutral  salt  of  ammonia  instantly 
assumes  a  purple  colour,  which  hoAvever  quickly  vanishes,  and  the  liquid 
becomes  turbid  from  the  formation  of  uramile ;  the  liquid  is  then  found  to 
contain  alloxan  and  free  acid.  With  oxide  of  silver,  alloxatin  disengages 
carbonic  acid,  reduces  a  poi'tion  of  the  metal,  and  converts  the  remainder 
of  the  oxide  into  oxalurate.  Boiled  with  water  and  binoxide  of  lead,  allox- 
antin gives  urea  and  carbonate  of  lead. 

MuEEXiDE ;  PURPUBATE  OF  AMBiONiA  OF  Dr,  Pbout. — There  are  several 
different  methods  of  preparing  this  magnificent  compound.  It  may  be  made 
directly  from  uric  acid,  by  dissolving  that  substance  in  dilute  nitric  acid, 
evaporating  to  a  certain  point,  and  then  adding  to  the  warm,  but  not  boiling 
liquid,  a  very  slight  excess  of  ammonia.  In  this  experiment  alloxantin  is 
first  produced,  which  becomes  afterwards  partially  converted  into  alloxan ; 
the  presence  of  both  is  requisite  to  the  production  of  murexide.  This  pro- 
cess is,  however,  very  precarious,  and  often  fails  altogether.  An  excellent 
method  is  to  boil  for  a  few  minutes  in  a  flask  a  mixture  of  1  part  of  dry 
uramile,  1  part  of  red  oxide  of  mercury,  and  40  parts  of  water,  to  which 
two  or  three  drops  of  ammonia  have  been  added ;  the  whole  assumes  in  a 
short  space  of  time  an  intensely  deep  purple  tint,  and  when  filtered  boiling- 
hot,  deposits,  on- cooling,  splendid  crystals  of  murexide,  unmixed  with  any 
impurity.  A  third,  and  perhaps  even  still  better  process,  is  that  of  Dr.  Gre- 
gory :  7  parts  of  alloxan  and  4  parts  of  alloxantin  are  dissolved  in  240  parts 
of  boiling  water,  and  the  solution  added  to  -about  80  parts  of  cold,  strong 
solution  of  carbonate  of  ammonia ;  the  liquid  instantly  acquires  such  a  depth 
of  colour  as  to  become  opaque,  and  gives  on  cooling  a  large  quantity  of  mu- 
rexide ;  the  operation  succeeds  best  on  a  small  scale. 

Murexide'  crystallizes  in  small  square  prisms,,  which  by  reflected  light 
exhibit  a  splendid  green  metallic  lustre,  like  that  of  the  wing-cases  of  the 
rose-beetle  and  other  insects ;  by  transmitted  light  they  are  deep  purple-red. 
It  is  soluble  with  difiiculty  in  cold  water,  much  more  easily  at  a  boiling  tem- 
perature, and  is  insoluble  in  alcohol  and  ether.  Mineral  acids  decompose  it 
with  separation  of  murexan,  and  caustic  potassa  dissolves  it,  with  production 
of  a  most  magnificent  purple  colour,  which  disappears  when  the  solution  is 
boiled.  Murexide  contains,  according  to  Liebig  and  Wohler,  CigTT^NgOg;  its 
production  may  be  thus  explained;  2  eq.  of  uramile  and  3  eq.  of  oxygen 
from  the  protoxide  of  mercury  give  rise  to  murexide,  1  eq.  of  alloxatiic 
acid,  and  3  eq,  of  water. 

2CJI5N3O6  -f  CO  =  C,2n6N50y,CJIN04  +  3110. 

Or,  on  the  other  hand,  1  eq.  of  alloxan,  2  eq.  of  alloxantin,  and  4  eq.  of 
ammonia,  yield  2  eq.  of  murexide  and  14  eq.  of  water. 

CaH^N^O^o  +  ^CsH,N,0,o  -f  4NH3  =  2C,,H,NA  +  14H0. 

*  80  called  from  the  I'yrian  dye,  said  to  hav  been  prepared  from  a  species  oimurea^  a  shell- 
fish 


XANTIIIC    OXIDE,    &c.  443 

MuREXAN ;  PURPURIC  A€iD  OP  Dr.  Prout. — Lie"big  directs  this  subjjtance 
to  be  prepared  by  dissolving  murexide  in  caustic  potassa,  heating  the  liquid 
until  the  colour  disappears,  and  then  adding  an  excess  of  dilute  suphuric 
acid.  It  separates  in  colourless  or  slightly  yellowish  scales,  nearly  insoluble 
in  cold  water.  In  ammonia  it  dissolves,  and  the  solution  acquires  a  purple 
colour  by  exposure  to  the  air,  the  murexide  being  then  produced.  Murexan 
is  said  to  contain  CgH4Nj05.  This  substance,  and  its  relation  to  murexide, 
require  re-examination. 

A  series  of  substances  closely  related  to  the  derivatives  of  uric  acid,  will 
be  noticed  under  the  head  of  Caffeine  (see  page  450). 

Connected  with  uric  acid  by  similarity  of  origin,  but  not  otherwise,  are 
two  curious  and  exceedingly  rare  substances,  called  zanthic  oxide  and  cystic 
oxide. 

Xanthic  oxide  was  discovered  by  Dr.  Marcet ;  it  occurs  as  an  urinary  cal- 
culus, of  pale  brown  colour,  foliated  texture,  and  waxy  lustre,  and  is  ex- 
tracted by  boiling  the  pulverized  stone  in  dilute  caustic  potassa  and  precipi- 
tating by  carbonic  acid.  The  xanthic  oxide  falls  as  a  white  precipitate,  which 
on  drying  becomes  pale  yellow,  and  resembles  wax  when  rubbed.  It  is 
nearly  insoluble  in  water  and  dilute  acids.  Its  characteristic  property  is  to 
dissolve  without  evolution  of  gas  in  nitric  acid,  and  to  give  on  evaporation  a 
deep  yellow  residue,  which  becomes  yellowish-red  on  the  addition  of  xmmonia 
or  solution  of  potassa.     Xanthic  oxide  gives  on  analysis  CsH^NgOj. 

Cystic  oxide. — Cystic  oxide  calculi,  although  very  rare,  are  more  frequently 
met  with  than  those  of  the  preceding  substance ;  they  have  a  pale  colour,  a 
concentric  structure,  and  often  a  waxy  external  crust.  The  powdered  cal- 
culus dissolves  in  great  part  without  effervescence  in  dilute  acids  and  alkalis, 
including  ammonia ;  the  ammoniacal  solution  deposits,  by  spontaneous  evapo- 
ration, small,  but  beautiful  colourless  crystals,  which  have  the  form  of  six- 
sided  prisms  and  square  tables.  It  forms  a  saline  compound  with  hydro- 
chloric acid.  Caustic  alkalis  disengage  ammonia  from  this  substance  by 
continued  ebullition.     Cystic  oxide  contains   sulphur;    it  is  composed  of 


Uric  acid  is  perfectly  well  characterized,  even  when  in  very  small  quantity, 
by  its  behaviour  with  nitric  acid.  A  small  portion  heated  with  a  drop  or 
two  of  nitric  acid  in  a  small  porcelain  capsule  dissolves  with  copious  effer- 
vescence. When  this  solution  is  cautiously  evaporated  nearly  to  dryness, 
and,  after  the  addition  of  a  little  water,  mixed  with  a  slight  excess  of  am- 
monia, the  deep  red  tint  of  murexide  is  immediately  produced. 

Impure  uric  acid,  in  a  remarkable  state  of  decomposition,  is  now  importer 
into  this  country  in  large  quantities,  for  use  as  a  manure,  under  the  nam« 
of  guano  or  huano.  It  comes  from  the  barren  and  uninhabited  islets  of  thi 
western  coast  of  South  America,  and  is  the  production  of  the  countless  birdd 
that  dwell  undisturbed  in  those  regions.  The  people  of  Peru  have  used  it 
for  ages.  Guano  usually  appears  as  a  pale  brown  powder,  sometimes  with 
whitish  specks ;  it  has  an  extremely  offensive  odour,  the  strength  of  which, 
however,  varies  very  much.  It  is  soluble  in  great  part  in  water,  and  the 
solution  is  found  to  be  extremely  rich  in  oxalate  of  ammonia,  the  acid  having 
been  generated  by  a  process  of  oxidation.  Guano  also  contains  a  peculiar 
substance  called  guanine^  which  closely  corresponds  with  xanthic  oxide.  Like 
urea,  it  combines  with  acids,  forming  a  series  of  crystallizable  salts.  Guanine 
cotitainB  r   TT  x,0,. 


444  VEGETO     ALKALIS. 


SECTION  V. 
THE   VEGETO-ALKALIS. 


The  vegeto-alkalis,  or  alkaloids,  or  organic  bases,  constitute  a  remarkable 
and  most  interesting  group  of  bodies  ;  they  are  met  with  in  various  plants, 
always  in  combination  with  an  acid,  which  is  in  many  cases  of  peculiar 
nature,  not  occurring  elsewhere  in  the  vegetable  kingdom.  They  are,  for 
the  most  part,  sparingly  soluble  in  water,  but  dissolve  in  hot  alcohol,  from 
which  they  often  crystallize  in  a  very  beautiful  manner  on  cooling.  Several 
of  them,  however,  are  oily,  volatile  liquids.  The  taste  of  these  substances, 
when  in  solution,  is  usually  intensely  bitter,  and  their  action  upon  the  animal 
economy  exceedingly  energetic.  They  all  contain  a  considerable  quantity 
of  nitrogen,  and  are  very  complicated  in  constitution,  having  high  combining 
numbers.     It  is  probable  that  these  bodies  are  very  numerous. 

None  of  the  organic  bases  occurring  in  plants  have  yet  been  formed  by 
artificial  means ;  analogous  substances  have,  however,  been  thus  produced. 

MoiiPHiNK,  OR  MORPHIA.  —  This  is  the  chief  active  principle  of  opium ;  it 
is  the  best  and  most  characteristic  type  of  the  group,  and  the  earliest  known, 
dating  back  to  the  year  1803. 

Opium,  the  inspissated  juice  of  the  poppy-capsule,  is  a  very  complicated 
substance,  containing,  besides  morphine,  a  host  of  other  alkaloids  in  very 
variable  quantities,  combined  with  sulphui'ic  acid  and  an  organic  acid  called 
the  meconic.  In  addition  to  these,  there  are  gummy,  resinous,  and  colouring 
matters,  caoutchouc,  &c.,  besides  mechanical  impurities,  as  chopped  leaves. 
The  opium  of  Turkey  is  the  most  valuable,  and  contains  the  largest  quantity 
of  morphine ;  that  of  Egypt  and  of  India  are  considerably  inferior.  It  has 
been  produced  in  England  of  the  finest  quality,  but  at  great  cost. 

If  ammonia  be  added  to  a  clear,  aqueous  infusion  of  opium,  a  very  abundant 
bufi'-coloured  or  brownish-white  precipitate  falls,  which  consists  principally 
of  morphine  and  narcotine,  rendered  insoluble  by  the  withdrawal  of  the  acid. 
The  product  is  too  impure,  however,  for  use.  The  chief  diflSculty  in  the 
preparation  of  these  substances  is  to  get  rid  of  the  colouring  matter,  which 
adheres  with  great  obstinacy,  re-dissolving  with  the  precipitates,  and  being 
again  in  part  thrown  down  when  the  solutions  ate  saturated  with  an  alkali. 
The  following  method,  which  succeeds  well  upon  a  small  scale,  will  serve  to 
give  the  student  some  idea  of  a  process  very  commonly  pursued  when  it  is 
desired  to  isolate  at  once  an  insoluble  organic  base,  and  the  acid  with  which 
it  is  in  combination : — A  filtered  solution  of  opium  in  tepid  water  is  mixed 
with  acetate  of  lead  in  excess :  the  precipitated  meconate  of  lead  is  separated 
by  a  filter,  and  through  the  solution  containing  acetate  of  morphine,  now 
freed  to  a  considerable  extent  from  colour,  a  stream  of  sulphuretted  hydrogen 
is  passed.  The  filtered  and  nearly  colourless  liquid,  from  which  the  lead 
has  been  thus  removed,  may  be  warmed  to  expel  the  excess  of  gas,  once 
more  filtered,  and  then  mixed  with  a  slight  excess  of  caustic  ammonia,  which 
throws  down  the  morphine  and  narcotine  ;  these  may  be  separated  by  boiling 
Mher,  in  which  the  latter  is  soluble.     The  meconate  of  lead,  well  washed, 


VEGETO-ALKALIS. 


445 


suspended  in  water,  and  decomposed  by  sulphuretted  hydrogen,  yields  solu- 
tion of  meconic  acid. 

]florphine  and  its  salts  are  advantageously  prepared,  on  the  large  scale,  by 
the  process  of  Dr.  Gregory.  A  strong  infusion  of  opium  is  mixed  with  a 
solution  of  chloride  of  calcium,  free  from  iron;  meconate  of  lime,  which  is 
nearly  insoluble,  separates,  while  the  hydrochloric  acid  is  transferred  to  the 
alkaloids.  By  duly  concentrating  the  filtered  solution,  the  hydrochlorate  of 
morphine  may  be  made  to  crystallize,  while  the  narcotine,  and  other  bodies, 
are  left  behind.  Repeated  recrystallization,  and  the  use  of  animal  charcoal, 
then  suffice  to  whiten  and  purify  the  salt,  from  which  the  base  may  be  pre- 
cipitated in  a  pure  state  by  ammonia.  Other  processes  have  been  proposed, 
as  that  of  M.  Thiboum^ry,  which  consists  in  adding  hydrate  of  lime  in  excess 
to  an  infusion  of  opium,  by  which  the  meconic  acid  is  rendered  insoluble, 
while  the  morphine  is  taken  up  with  ease  by  the  alkaline  earth.  By  exacUij 
neutralizing  the  filtered  solution  with  hydrochloric  acid,  the  morphine  is  pre- 
cipitated, but  in  a  somewhat  coloured  state. 

Morphine,  when  crystallized  from  alcohol,  forms  small,  but  very  brilliant 
prismatic  crystals,  which  are  transparent  and  colourless.  It  requires  at  least 
1000  parts  of  water  for  solution,  tastes  slightly  bitter,  and  has  an  alkaline 
reaction.  These  efi'ects  are  much  more  evident  in  the  alcoholic  solution.  It 
dissolves  in  about  30  parts  of  boiling  alcohol,  and  with  great  facility  in  dilute 
acids ;  it  is  also  dissolved  by  excess  of  caustic  potassa  or  soda,  but  scarcely 
by  excess  of  ammonia.  When  heated  in  the  air,  morphine  melts,  inflames 
like  a  resin,  and  leaves  a  small  quantity  of  charcoal,  which  easily  burns  away. 

Morphine,  in  powder,  strikes  a  deep  bluish  colour  with  neutral  salts  of 
sesquioxide  of  iron,  decomposes  iodic  acid  with  liberation  of  iodine,  and  forma 
a  deep  yellow  or  red  compound  with  nitric  acid ;  these  reactions  are  by  some 
considered  characteristic. 

Crystalline  morphine  contains  Cg^HigNOg-j-SIIO. 

The  most  characteristic  and  best-defined  salt  of  this  substance  is  the 
hydrochlorate.  It  crystallizes  in  slender,  colourless  needles,  arranged  in  tufts 
or  stellated  groups,  soluble  in  about  20  parts  of  cold  water,  and  in  its  own 
weight  at  a  boiling  temperature.  The  crystals  contain  6  eq.  of  water.  The 
sulphate,  nitrate,  and  phosphate  are  crystallizable  salts ;  the  acetate  crystallizes 
with  great  difficulty,  and  is  usually  in  the  state  of  a  dry  powder.  The  arti- 
ficial meconate  is  sometimes  prepared  for  medicinal  use. 

Narcotine. — The  marc,  or  insoluble  portion  of  opium,  contains  much  nar- 
cotine, which  may  be  extracted  by  boiling  with  dilute  acetic  acid.  From  the 
filtered  solution  the  narcotine  is  precipitated  by  ammonia,  and  afterwards 
purified  by  soiutioTi  in  boiling  alcohol,  and  filtration  through  animal  charcoal. 
Narcotine  crystallizes  in  small,  colourless,  brilliant  prisms,  which  are  nearly 
insoluble  in  water.  The  basic  powers  of  narcotine  are  very  feeble ;  it  is  des- 
titute of  alkaline  reaction,  and,  although  freely  soluble  in  acids,  refuses,  for 
the  most  part,  to  form  with  them  crystallizable  compounds. 

According  to  Dr.  Blyth,  narcotine  contains  C4gH25NO,4. 

Narcotine  yields  some  curious  products  by  the  action  of  oxidizing  agents, 
as  a  mixture  of  dilute  sulphuric  acid  and  binoxide  of  manganese,  or  a  hot 
solution  of  bichloride  of  platinum.  They  have  been  chiefly  studied  by  Wohler 
and  Blyth,  and  lately  also  by  Anderson.  The  most  important  of  these  is 
opianic  acid,  a  substance  forming  colourless,  prismatic,  reticulated  crystals, 
sparingly  soluble  in  cold  water,  easily  in  hot.  It  melts  when  heated,  but 
does  not  sublime.  After  fusion  it  becomes  quite  insoluble  in  dilute  alkalis, 
but  without  change  of  composition.  This  acid  forms  crystallizable  salts  and 
an  ether :  it  contains  CjoHgOgHO.  The  ammonia-salt,  by  evaporation  to  dry- 
ness, yields  -a  nearly  white  insoluble  powder,  called  opiammon,  containing 
C^gHjgNOig,  convertible  by  strong  acids  into  opianic  acid  and  ammonia.    Sul- 


446  VEGETO-ALKALIS. 

phurous  acid  yields  with  opianic  acid  two  products  containing  sulphur.  A 
mixture  of  binoxide  of  lead,  opianic  acid,  and  sulphuric  acid  gives  rise  to  a 
crystallizable  bibasic  acid  termed  hemipinic  acid,  containing  C2oHgO,o,2HO. 
A  basic  substance,  cotarnine,  CagHigNOg,  is  contained  in  the  mother-liquor 
from  which  opianic  acid  has  crystallized ;  it  forms  a  yellow  crystalline  mass, 
very  soluble,  of  bitter  taste,  and  feebly  alkaline  reaction.  Its  hydrochlorate 
is  a  well-defined  salt.  Another  basic  substance,  narcogenine,  was  accidentally 
produced  in  an  attempt  to  prepare  cotarnine  by  bichloride  of  platinum.  It 
formed  large  orange-coloured  needles,  and  contained  CggHjgNOio. 

Codeine.  —  Hydrochlorate  of  morphine,  prepared  directly  from  opium  as 
in  Gregory's  process,  contains  codeine-salt.  When  dissolved  in  water,  and 
mixed  with  a  slight  excess  of  ammonia,  the  morphine  is  precipitated,  and 
the  codeine  left  in  solution.  Pure  codeine  crystallizes,  by  spontaneous  evapo- 
ration, in  colourless  transparent  octahedrons;  it  is  soluble  in  80  parts  of 
cold,  and  17  of  boiling  water,  has  a  strong  alkaline  reaction,  and  forms  crys- 
tallizable salts. 

Codeine  is  composed  of  CgeHjiNOg.  This  has  lately  been  the  subject  of  a 
careful  investigation  by  Dr.  Anderson,  who  has  prepared  a  great  number  of 
its  derivatives,  all  of  which  establish  the  formula  given. 

Trebaine  or  paramorphine. — This  substance  is  contained  in  the  preci- 
pitate formed  by  hydrate  of  lime  in  a  strong  infusion  of  opium  in  Thibou- 
m6ry's  process  for  morphine.  The  precipitate  is  well  washed,  dissolved  in 
dilute  acid,  and  mixed  with  ammonia  in  excess,  and  the  thebaine  thrown 
down,  crystallized  from  alcohol.  It  forms  when  pure  colourless  needles  like 
those  of  narcotine,  but  sparingly  soluble  in  water,  readily  soluble  in  the  cold 
in  alcohol  and  ether.  It  melts  when  heated,  and  decomposes  at  a  high  tem- 
perature. With  dilute  acids  it  forms  crystallizable  compounds,  and  when 
isolated  and  in  solution  has  a  powerful  alkaline  reaction.  The  composition 
of  thebaine  is  CggHjjNOg. 

A  series  of  other  bases,  pseudo-morphine,  narceine,  meconine,  papaveriney 
opianine,  and porphyroxine,  are  also,  at  least  occasionally,  contained  in  opium; 
they  are  of  small  importance,  and  comparatively  little  is  known  respecting 
them. 

Meconic  acid  is  obtained  from  the  impure  meconate  of  lead,  as  already 
mentioned.  The  solution  is  evaporated  in  the  vacuum  of  the  air-pump.  A 
more  advantageous  method  is  to  decompose  the  impure  meconate  of  lime, 
obtained  in  Dr.  Gregory's  morphine-process,  by  warm  dilute  hydrochloric 
acid ;  to  separate  the  crystals  of  acid  meconate  of  lime,  which  form  on 
cooling,  and  to  repeat  this  (operation  until  the  whole  of  ^he  base  has  been 
removed,  which  may  be  known  by  the  acid  being  entirely  combustible,  with- 
out residue,  when  heated  in  the  flame  of  a  spirit-lamp  upon  platinum  foil. 
It  is  with  the  greatest  difficulty  obtained  free  from  colour. 

Meconic  acid  crystallizes  in  little  colourless,  pearly  scales,  which  dissolve 
in  4  parts  of  hot  water.  It  has  an  acid  taste  and  reaction,  forms  soluble 
compounds  with  the  alkalis,  and  insoluble  salts  with  lime,  baryta,  and  the 
oxides  of  lead  and  silver.  The  most  remarkable  feature  in  this  substance  is 
its  property  of  striking  a  deep  blood-red  colour  with  a  salt  of  the  sesqui- 
oxide  of  iron,  exactly  resembling  that  developed,  under  similar  circum- 
stances, by  a  sulphocyanide.  The  meconate  of  iron  may,  however,  be  dis- 
tinguished from  the  latter  compound,  as  Mr.  Everitt  has  shown,  by  an  addi- 
tion of  corrosive  sublimate,  which  bleaches  the  sulphocyanide,  but  has  little 
effect  upon  the  meconate.  This  is  a  point  of  considerable  practical  impor- 
tance, as  in  medico-legal  inquiries,  in  which  evidence  of  the  presence  of 
opium  is  sought  for  in  complex  organic  mixtures,  the  detection  of  meconic 
%cid  is  usually  the  object  of  the  chemist;  and  since  traces  of  alkaline  sul- 


VEG.ETO-ALKALIS.  447 

phocyanide  are  to  be  found  in  the  saliva,  it  becomes  very  desiraole  to  remove 
that  source  of  error  and  ambiguity. 

Crystallized  meconic  acid  contains  Cj4HO,j,3HO-j-6HO. 

When  a  solution  of  meconic  acid  in  water,  or,  still  better,  in  a  mineral 
acid,  is  boiled,  or  when  the  dry  acid  is  exposed  in  a  retort  to  a  temperature 
of  400°  (204°-5C),  it  is  decomposed,  yielding  a  new  bibasic  acid,  the  comenicy 
containing  C,2H20g,2HO,  which  much  resembles  in  properties  meconic  acid. 
Water  and  carbonic  acid  are  at  the  same  time  extricated.  At  a  higher  tem- 
perature comenic  acid  itself  is  resolved  into  a  second  new  acid,  the  pyrome- 
conic,  which  sublimes,  and  afterwards  condenses  in  brilliant  colourless  plates. 
It  is  monobasic,  and  contains  CjoHgOg.HO.  The  salts  of  meconic  acid  and 
comenic  acid,  together  with  several  derivatives  of  these  substances,  have 
been  lately  studied  by  Mr.  How,'  but  our  space  will  not  permit  us  to  describe 
these  compounds. 

An  acid  much  resembling  the  meconic  has  been  extracted  from  the  Cheli- 
doniuin  majus ;  it  is  combined  with  lime,  and  associated  with  malic  and  fu- 
maric  acids.  Chelidonic  acid  is  bibasic,  forming  three  classes  of  salts,  and 
a  pyro-acid  with  evolution  of  water  and  carbonic  acid  when  exposed  to  a  high 
temperature.  It  crystallizes  in  slender  colourless  needles  of  considerable 
solubility,  containing  C,4H20io,2HO-f  3H0. 

CiNCHONiNE  AND  QUININE. — It  is  to  thcsc  vegcto-alkalis  that  the  valuable 
medicinal  properties  of  the  Peruvian  barks  are  due.  They  are  associated  in  the 
bark  with  sulphuric  acid,  and  with  a  special  acid,  not  found  elsewhere,  called 
the  kinic.  Cinchonine  is  contained  in  largest  quantity  in  the  pale  bark,  or 
Cinchona  condaminea  ;  quinine  in  the  yellow  bark,  or  Cinchona  cordifolia  ;  the 
Cinchona  oblongifoUa  contains  both. 

The  simplest,  but  not  the  most  economical,  method  of  preparing  these 
substances,  is  to  add  a  slight  excess  of  hydrate  of  lime  to  a  strong  decoction 
of  the  ground  bark,  in  acidulated  water;  to  wash  the  precipitate  which 
ensues,  and  boil  it  in  alcohol.  The  solution,  filtered  while  hot,  deposits  the 
vegeto-alkali  on  cooling.  When  both  bases  are  present,  they  may  be  sepa- 
rated by  converting  them  into  sulphates;  the  salt  of  quinine  is  the  least 
soluble  of  the  two,  and  crystallizes  first. 

Pure  cinchonine  or  cinchonia,  crystallizes  in  small,  but  beautifully  bril- 
liant, transparent  four-sided  prisms.  It  is  but  very  feebly  soluble  in  water, 
dissolves  readily  in  boiling  alcohol,  and  has  but  little  taste,  although 
its  salts  are  excessively  bitter.  It  is  a  powerful  base,  neutralizing  acids 
completely,  and  forming  a  series  of  crystallizable  salts. 

Quinine,  or  quina,  much  resembles  cinchonine ;  it  does  not  crystallize  so 
well,  however,  and  is  much  more  soluble  in  water ;  its  taste  is  intensely 
bitter. 

Cinchonine  is  composed  of CjjoHijNO,  and 

Quinine  of CgoHjaNOg.' 

Sulphate  of  quinine  is  manufactured  on  a  very  large  scale  for  medicinal 
use  ;  it  crystallizes  in  small  white  needles,  which  give  a  neutral  solution. 
Nevertheless,  this  substance  is  a  basic  salt,  and  contains  2C20H  jjN 03,803 -f- 
8H0.  The  solubility  of  this  compound  is  much  increased  by  the  addition  of 
a  little  sulphuric  acid,  whereby  the  neutral  salt  CgoHigNOajSO^-f-SHO  is 
formed.     A  very  interesting  compound  has  been  lately  produced  by  Dr. 

»  Chem.  Sec.  Quar,  Jour.    Vol.  IV.  page  SaS. 

^  Some  doubts  are  still  hanging  over  the  composition  of  cinchonine  and  quinine.  Accord- 
ing to  M.  Lavrent  these  substances  contain  respectively  CsjHiMNsO^,  and  CsellMNaOi.  If  these 
formulte  be  adopted  the  basic  sulphate  of  commerce  would  become  a  neutral,  the  neutr<il 
«n  acid-salt. 

Commercial  sulphate CsslTa^N^OjSOs-f  8H0 

Soluble  sulphate C36ll34N2O2,S03+H0,S03-{-15H0. 


448  VEGETO-ALKALIS. 

Herapath,  by  the  action  of  iodine  upon  the  sulphate  of  quinine.  It  is  a 
crystalline  substance  of  a  brilliant  emerald  colour,  which  appears  to  consist 
of  1  e(i.  of  the  sulphate  of  quinine,  and  1  eq.  of  iodine.  This  remarkable 
compound  possesses  the  optical  properties  of  the  mineral  tourmaline.  (See 
page  75.) 

Quinidine, — In  manufacturing  sulphate  of  quinine,  a  new  base  has  been 
lately  obtained,  which  differs  from  quinine  in  some  of  its  physical  proper- 
ties, but  is  said  to  have  the  same  composition  as  quinine.  It  has  been 
described  under  the  name  of  quinidine,  and  appears  to  have  the  same  medi- 
cinal properties  as  quinine.  ^his  substance  is  not  yet  sufficiently  ex- 
amined.' 

Chinoidine,  quinoidine,  or  amorphous  quinine,  is  contained  in  the  refuse,  or 
mother-liquors  of  the  quinine-manufacture.  In  its  purest  state  it  forms  a 
yellow  or  brown  resin-like  mass,  insoluble  in  water,  freely  soluble  in  alcohol 
and  ethoy.  It  is  easily  soluble  h.lso  in  dilute  acids,  and  is  thence  precipitated 
by  ammonia.  Quinoidine  possesses  powerful  febrifuge  properties,  and  is 
identical  in  composition  with  qtiinine.  It  evidently  bears  to  quinine  the  same 
relation  that  uncrystallizable  syrup  does  to  ordinary  sugar,  being  produced 
from  quinine  by  the  heat  employed  in  the  preparation.'* 

From  Cusco,  or  Arica-hark,  and  likewise  from  the  Cinchona  ovata,  or  white 
quinquina  of  Condamine,  a  substance  denominated  aricine  or  cinchovatine  has 
been  extracted ;  it  closely  resembles  cinchonine,  and  contains  CjoHjgNOj  i.  e. 
1  eq.  of  oxygen  more  than  quinine,  and  2  eq.  more  than  cinchonine. 

This  substance  is  useless  in  medicine. 

KiNic  ACID. — Kinate  of  lime  is  found  in  the  solution  from  which  the  bark- 
alkalis  have  been  separated  by  hydrate  of  lime,  and  is  easily  obtained  by 
evaporation,  and  purified  by  animal  charcoal.  From  the  lime-salt  the  acid 
can  be  extracted  by  decomposing  it  by  diluted  sulphuric  acid.  The  clear 
solution  evaporated  to  a  syrupy  consistence  deposits  large,  distinct  crystals, 
which  resemble  those  of  tartaric  acid.  It  is  soluble  in  2  parts  of  water, 
and  contains  Ci4HjiOu,HO. 

When  kinic  acid  is  heated  with  a  mixture  of  sulphuric  acid  and  binoxide 
of  manganese,  it  furnishes  a  very  volatile  substance  termed  kinone,  the 
vapour  of  which  is  exceedingly  irritating  to  the  eyes.  This  new  body  forms 
crystals  both  by  sublimation  and  by  solution  in  boiling  water ;  it  melts  with 
gentle  heat,  and  crystallizes  on  cooling,  colours  the  skin  permanently  brown, 
and  contains  C12H4O4. 

By  destructive  distillation,  kinic  apid  yields  numerous  and  interesting  pro- 
ducts, which  have  been  studied  by  M.  Wohler,  as  benzoic  acid,  carbolic  acid, 
hydride  of  salicyl,  benzol,  a  tarry  substance  not  examined,  and  a  new  body, 
colourless  hydrokinone,  which  possesses  very  curious  relations  with  the  kinone 
above  described.  It  forms  colourless  six-sided  prismatic  crystals  ;  is  neu- 
tral, destitute  of  taste  and  odour,  fusible,  and  easily  soluble  both  in  water 

*  Quina  is  very  soluble  in  alcohol  and  ether;  its  sulphate  requires  57  parts  of  absolute 
and  63  of  alcohol  of  90  per  cent,  for  solution  ;  of  water  265  parts  of  cold  and  24  of  boiling 
are  required.    The  oxalate  is  completely  insoluble  in  water. 

Quinidine  differs  in  separating  from  its  solution  in  alcohol  in  crystals,  in  its  inferior  solu- 
bility in  alcohol  and  ether,  and  the  greater  solubility  of  its  sulphate  in  water.  It  dissolves 
in  140  to  150  parts  of  ether,  45  of  absolute  and  105  of  alcohol  of  90  per  cent.  Its  sulphate 
in  soluble  in  32  parts  of  absolute  and  7  parts  of  alcohol  of  90  per  cent.,  in  73  parts  of  cold 
and  less  than  5  of  boiling  water,  according  to  Howard  (130  of  620-6  (17°C)  and  16  of  boiling 
water.— Leers).  The  oxalate  is  very  soluble  in  cold  and  more  freely  in  boiling  water,  from 
which  crystals  are  deposited  on  cooling. 

Quinidine  contains  CisHnNO. — R.  B. 

«  Amorphous  quinine  is  a  mixture  of  quina,  cinchonia,  and  a  resin.  Quina  may  be  ob- 
tained from  it  by  dissolving  in  alcohol,  precipitating  by  protochloride  of  tin,  filtering,  and 
adding  ammonia  to  the  clear  liquor.  The  precipitate  well  washed  and  dried,  and  a  second 
time  treated  with  protochloride  of  tin  and  ammonia,  yields  to  alcohol  pure  quina,  which 
crystallizes  on  evaporating  the  alcohol,— R.  B. 


VEGETO-ALKALIS.  44^ 

and  alcohol.     With   care  it  may  be   sublimed   unchanged.      It   contains 
CuHg04. 

Colourless  hydrokinone  can  be  easily  and  directly  produced  from  kinone 
by  the  assimilation  of  hydrogen,  as  by  addition  of  hydriodic  acid  to  a  solu- 
tion of  the  latter,  when  iodine  is  set  free,  or  by  sulphurous  acid,  or  tellu- 
retted  hydrogen. 

An  intermediate  product  of  reduction  is  green  hydrokinone.  This  is  ob- 
tained by  the  incomplete  action  of  sulphurous  acid  upon  kinone,  or  by  the 
action  of  sesquichloride  of  iron,  chlorine,  nitrate  of  silver,  or  chromic  acid 
upon  colourless  hydrokinone  ;  or  by  mixing  together  solutions  of  kinone  and 
colourless  hydrokinone.  It  forms  slender  green  crystals  of  the  colour  of  the 
wing-case  of  the  rose-beetle,  and  of  the  greatest  brilliancy  and  beauty.  It 
is  fusible,  has  but  little  odour,  and  dissolves  freely  in  boiling  water,  crys- 
tallizing out  on  cooling.     This  substance  contains  0,311504. 

If  kinic  acid  be  submitted  to  distillation  with  an  ordinary  chlorine-mix- 
ture, an  acid  liquid  and  a  crystalline  sublimate  are  formed.  The  former  is 
a  solution  of  formic  acid,  the  latter  a  mixture  of  4  chlorinetted  compounds, 
which  are  chlorokinone  C,2(E[3C1)04,  bichlorokinone  Ci2(H2Cl2)04,  trichloro- 
kinone  C,2(HCl3)04  and  tetrachlorokinone  C12CI4O4.  They  are  all  yellow 
crystalline  substances,  which  can  be  separated  only  with  great  difficulty. 
Like  kinone  itself,  they  possess  the  faculty  of  combining  with  1  or  2  eq.  of 
hydrogen,  producing  2  series  of  substances  analogous  to  green  and  colour- 
less hydrokinone.  Tetrachlorokinone,  better  known  by  the  name  chloranile, 
likewise  occurs  among  the  products  of  decomposition  of  indigo. 

Other  products  were  obtained  by  the  action  of  sulphuretted  hydrogen  and 
strong  hydrochloric  acid  upon  kinone,  which  possess  loss  interest  than  the 
preceding. 

Strychnine  and  brucinb,  also  called  strychnia  and  brucia,  are  contained 
in  Nux  vomica,  in  St.  Ignativ£  heart,  and  in  fake  Angtistura  hark ;  they  are 
associated  with  a  peculiar  acid,  called  the  igasuric.  Nux  vomica  seeds  are 
boiled  in  dilute  sulphuric  acid  until  they  become  soft ;  they  are  then 
crushed,  and  the  expressed  liquid  mixed  with  excess  of  hydrate  of  lime, 
which  throws  down  the  alkalis.  The  precipitate  is  boiled  in  spirit  of  wine 
of  sp.  gr.  0-850,  and  filtered  hot.  Strychnine  and  brucine  are  deposited 
together  in  a  coloured  and  impure  state,  and  may  be  separated  by  cold 
alcohol,  in  which  the  latter  dissolves  readily. 

Pure  strychnine  crystallizes  under  favourable  circumstances  in  small,  but 
exceedingly  brilliant  octahedral  crystals,  which  are  transparent  and  colour- 
less. It  has  a  very  bitter,  somewhat  metallic  taste  (1  part  in  1,000,000  parts 
of  water  is  still  perceptible),  is  slightly  soluble  in  water,  and  is  fearfully 
poisonous.  It  dissolves  in  hot,  and  somewhat  dilute  spirit,  but  neither  in 
absolute  alcohol,  ether,  nor  in  solution  of  caustic  alkali.  This  alkaloid  may 
be  readily  identified  by  moistening  a  crystal  with  concentrated  sulphuric 
acid,  and  adding  to  the  liquid  a  crystal  of  bichromate  of  potassa,  when  a 
deep  violet  tint  is  produced,  which  disappears  after  some  time.  Strychnine 
forms  with  acids  a  series  of  well-defined  salts,  lately  examined  by  Messrs. 
Nicholson  and  Abel,  who  established  for  strychnine  the  formula  C42H22N2O4 

Brucine  is  easily  distinguished  from  the  preceding  substance,  which  it 
much  resembles  in  many  respects,  by  its  ready  solubility  in  alcohol,  both 
hydrate  and  absolute.  It  dissolves  also  in  about  500  parts  of  hot  water. 
The  salts  of  brucine  are,  for  the  most  part,  crystallizable. 

Brucine  contains  C4gH26N20s- 

VERATKrNE  (or  vcratria)  is  obtained  from  the  seeds  of  Veratriim  sabadilla 

In  its  purest  state  it  is  a  white,  or  yellowish-white  powder,  which  has  a  sharp 

burning  taste,  and  is  very  poisonous.  It  is  remarkable  for  occasioning  violent 

sneezing.     It  is  insoluble  in  water,  but  dissolves  in  hot  alcohol,  in  ether,  and 

?.8* 


450  VEQETO-AL  KALIS. 

in  acids  )  the  solution  has  an  alkaline  reaction.  Veratrine  contains  nitrogen, 
but  its  composition  is  yet  doubtful.' 

A  substance  called  colchicine,  extracted  from  the  Colchicum  autumnale,  and 
formerly  confounded  with  veratrine,  is  now  considered  distinct ;  its  history 
is  yet  imperfect. 

Conine  (conicine,  or  conia),  nicotine,  and  sparteine,  differ  from  the 
other  vegetable  bases  in  physical  characters  ;  they  are  volatile  oily  liquids. 
The  first  is  extracted  from  hemlock,  the  second  from  tobacco,  and  the  third 
from  broom  {spartium  scoparium).  They  agree  in  most  of  their  characters, 
having  high  boiling-points,  very  poisonous  properties,  strong  alkaline  reaction, 
and  the  power  of  forming  with  acids  crystallizable  salts.  The  formula  of 
nicotine  is  CiqH^N  ;  that  of  conine,  CjgHjgN,  and  that  of  sparteine  CigH^N. 
A  series  of  substances  as  it  appears  closely  related  to  nicotine  will  be  men- 
tioned among  the  artificial%3rganic  bases. 

The  basic  substance  contained  in  the  juice  of  aniinal  flesh,  kreatinine,  will 
be  found  described  among  the  components  of  the  animal  body. 

Harmaline.  —  This  compound  is  extracted  by  dilute  acetic  acid  from  the 
seeds  of  the  Peganum  harmala,  a  plant  which  grows  abundantly  in  the  Steppes 
of  Southern  Russia,  and  the  seeds  of  which  are  used  in  dyeing.  When  pure, 
it  forms  yellowish  prismatic  crystals,  soluble  in  alcohol  and  dilute  acids,  but 
scarcely  forming  crystallizable  salts.  By  oxidation  it  gives  rise  to  another 
compound,  harmine,  which  itself  possesses  basic  properties.  The  seeds  are 
used  for  dyeing.     Harmaline  probably  contains  CjgHj^NjOj,  and  harmine 

Caffeine,  or  tiieine.  —  This  remarkable  substance  occurs  in  four  articles 
of  domestic  life,  infusions  of  which  are  used  as  a  beverage  over  the  greater 
part  of  the  known  world,  namely,  tea  and  coffee,  and  the  leaves  of  Guarana 
officinalis,  or  Paullinia  sorbilis,  and  in  those  of  Ilex  paraguayensis ;  it  will  pro- 
bably be  found  in  other  plants.  A  decoction  of  common  tea,  or  of  raw  coffee- 
berries,  previously  crushed,  is  mixed  with  excess  of  solution  of  basic  acetate 
of  lead.  The  solution,  filtered  from  the  copious  yellow  or  greenish  precipi- 
tate, is  treated  with  sulphuretted  hydrogen  to  remove  the  lead,  filtered, 
evaporated  to  a  small  bulk,  and  neutralized  by  ammonia.  The  caffeine 
crystallizes  out  on  cooling,  and  is  easily  purified  by  animal  charcoal.  It 
forms  tufts  of  delicate,  white,  silky  needles,  which  have  a  bitter  taste,  melt 
when  heated  with  loss  of  water,  and  sublime  without  decomposition.  It  is 
soluble  in  about  100  parts  of  cold  water,  and  much  more  easily  at  a  boiling- 
heat,,  or  if  an  acid  be  present.  Alcohol  also  dissolves  it,  but  not  easily. 
Caffeine  contains  C,eH,(,N204.  The  basic  properties  are  feeble.  The  salts 
with  hydrochloric  and  sulphuric  acid  are  obtained  only  with  difficulty.  It 
forms,  however,  splendid  double-salts  with  bichloride  of  platinum  and  ter- 
chloride  of  gold.  The  products  of  oxidation  of  caffeine,  which  have  been 
lately  studied  by  Rochleder,  are  of  considerable  interest,  inasmuch  as  both 
their  composition  and  their  properties  establish  a  close  connection  of  these 
products  with  the  derivatives  of  uric  acid.  Under  the  influence  of  chlorine, 
caffeine  yields  a  substance  of  feebly  acid  properties,  which  contains  CjgHYNjOg. 
This  compound,  which  has  received  the  name  amalic  acid,  is  homologous  to 
alloxantin.  When  treated  with  oxidizing  agents,  it  yields  cholesirophane, 
CjQiTgNgOg,  the  parabanic  acid  of  the  uric  acid-series.  The  murexide  of  the 
caffeine-series  lastly  is  formed  by  the  treatment  of  amalic  acid  with  ammonia, 

*  According  to  Courbe,  it  contains  C34II22NO6.  Several  of  these  bases  may  be  distinguished 
by  nitric  acid.  Brucia  becomes  bright  red,  which  is  soon  changed  to  purple  by  chloride  of 
till.  Pure  strychnine  becomes  yellow.  Veratria,  orange  red,  soon  chaugi'ig  to  yellow. 
Morphia,  bright  red,  changed  to  yellow  by  chloride  of  tin. — R.  B. 


VEGETO- ALKALIS.  45' 

exactly  as  the  murexide  par  excellence  is  formed  by  the  action  of  ammonia 
upon  alloxantin.  The  new  murexide  imitates  its  prototype  not  only  in  com- 
position, but  likewise  in  the  green  metallic  lustre  of  its  crystals,  and  the 
deep  crimson  colour  of  its  solutions.  The  homology  of  these  compounds 
with  the  members  of  the  uric  acid-series  is  well  illustrated  by  a  comparison 
of  their  formulae  — 

Alloxantin         Cg  HgNgOg-f-^CaHgssCigH,^  NgOg  Amalic  acid 
Parabanic  acid  Cg  H2N2064-2C2H2=C,oHg  NgOg  Cholestrophane 
Murexide  Cj2H6N508-f-3C2H2=C,8H,2N508  Caffeine-murexide 

Theobromine. — The  seeds  of  the  Theohroma  cacao,  or  cacao-nuts,  from 
•wliich  chocolate  is  prepared,  contain  a  crystallizable  principle  to  which  the 
preceding  name  is  given.  It  is  extracted  in  the  same  manner  as  caifeine, 
and  forms  a  white,  crystalline  powder,  which  is  much  less  soluble  than  the 
last-named  substance.  It  contains,  according  to  Glasson,  C,4HgN404.  Ac- 
cordingly it  is  homologous  to  caffeine.  The  products  obtained  from  theo- 
bromine by  oxidation  appear  to  be  likewise  homologous  with  terms  of  the 
uric  acid-series. 

Berberine. — A  substance  crystallizing  in  fine  yellow  needles,  slightly 
soluble  in  water,  extracted  from  the  root  of  the  Berberis  vulgaris.  It  has 
feeble  basic  properties,  and  contains  C^aHjgNOg.  This  must  not  be  confounded 
with  beeherine,  an  uncrystallizable  basic  substance,  from  the  bark  of  the 
green-heart  timber  of  Guiana,  which"  has  the  composition  C38H2iNOe.  It  forms 
with  acids  uncrystallizable  salts. 

PiPERiNE. — A  colourless,  or  slightly  yellow  crystallizable  principle,  ex- 
tracted from  pepper  by  the  aid  of  alcohol.  It  is  insoluble  in  water.  Formula 
Cg^HjgNOg.  Piperine  readily  dissolves  in  acid  ;  definite  compounds  however 
are  obtained  only  with  difficulty. 

There  are  very  many  other  bodies,  more  or  less  perfectly  known,  having 
to  a  certain  extent  the  properties  of  salt-bases ;  the  following  statement  of 
the  names  and  mode  of  occurrence  of  a  few  of  these  must  suffice, 

Hyoscyamine  [Daturine). — A  white,  crystallizable  substance,  from  Hyos- 
cyamus  niger  ;  it  occurs  likewise  in  Datura  stramonium,  formula  C34H23NO5. 

Atropine.  —  Colourless  needles,  from  Atropa  belladonna,  formula  C34H23NO6.* 

Solanine. — A  pearly,  crystalline  substance,  from  various  solanaceous  plants. 

Aconitine. — A  glassy,  transparent  mass,  from  Aconitum  napellus:  formula 

Ddphinine. — A  yellowish,  fusible  substance,  from  the  seeds  of  Delphinium 
staphisagria. 

Emetine. — A  white  and  nearly  tasteless  powder  from  ipecacuanha  root. 
Curarine. — The  arrow-poison  of  Central  America. 


There  exists  an  extensive  series  of  neutral,  usually  bitter,  and  sometimes 
poisonous  vegetable  principles,  which  are  allied  in  some  measure  to  the 
vegeto-alkalis.  Some  of  these  are  destitute  of  nitrogen.  Two  of  the  num- 
ber, salicin  and  phloridzan,  have  been  already  described  (see  pages  403  and 
40G) ;  the  most  important  of  the  remainder  are  the  following : — 

Gentianin. — The  bitter  principle  of  the  gentian-root,  extracted  by  ether. 

*  Crystallizes  from  a  saturated  hot  aqueous  solution  in  silky  tufts;  colourless,  inodorous, 
■very  bitter,  soluble  in  25  parts  of  ether,  2000  parts  cold  and  54  of  hot  water.  Has  a  strong 
alkaline  reaction,  and  forms  crystallizable  salts.    It  is  probably  identical  with  daturine  — 

*  Crystallizes  from  an  alcoholic  solution  in  small  grains ;  soluble  readily  in  alcohol  and 
ether,  and  also  in  100 parts  cold  and  50  boiling  water;  has  a  sharp,  bitter  taste,  and  alkaline 
reaction.    Its  salts  are  not  crystallizable. — R.  B. 


452  VEGETO-ALKALIS. 

It  crystallizes  in  golden-yellow  needles,  is  sparingly  soluble  in  cold  water, 
more  soluble  in  hot  water,  and  freely  dissolved  by  alcohol  and  ether.  Its 
composition  is  C14H5O5. 

PoPULiN. — This  substance  closely  resembles  salicin  in  appearance  and  solu- 
bility, but  has  a  penetrating  sweet  taste  ;  it  is  found  accompanying  salicin  in 
the  bark  and  leaves  of  the  aspen.  According  to  recent  researches  of  Piria, 
popiiliu  contains  C4oH220,6-f-4HO.  It  is  a  conjugate  compound  of  salicin  and 
benzoic  acid. 

C40H26O20         =         C,4He04         +         C2eH,„O,4-J-2H0 

Crystall.  Populin.  Benzoic  acid.  Salicin. 

By  the  action  of  reagents  it  is  converted  into  benzoic  acid,  and  the  products 
of  decomposition  of  salicin.  With  dilute  acid  it  yields  benzoic  acid,  grape- 
sugar,  and  saliretin;  when  treated  with  a  mixture  of  sulphuric  acid  and 
bichromate  of  potassa,  it  furnishes  a  considerable  quantity  of  hydride  of 
salicyl. 

Daphnin. — Extracted  from  the  bark  of  the  Daphne  mezereum;  it  forms 
colourless,  radiated  needles,  freely  soluble  in  hot  water,  alcohol  and  ether. 

Hesperidin. — A  white,  silky,  tasteless  substance,  obtained  from  the  spongy 
part  of  oranges  and  lemons.  It  dissolves  in  60  parts  of  hot  water ;  also  in 
alcohol  and  ether. 

Elaterin. — The  active  principle  of  Momordica  elaterium.  It  is  a  white, 
silky,  crystalline  powder,  insoluble  in  water.  It  has  a  bitter  taste,  and  ex- 
cessively violent  purgative  properties.  Alcohol,  ether,  and  oils  dissolve  it. 
Exposed  to  heat,  it  melts  and  afterwards  volatilizes.     It  contains  CgoHj^Og. 

Antiarin. — The  poisonous  principle  of  the  Upas  antiar.  It  forms  small, 
pearly  crystals,  soluble  in  27  parts  of  boiling  water,  and  also  in  alcohol,  but 
scarcely  so  in  ether;  it  cannot  be  sublimed  without  decomposition.  Intro- 
duced into  a  wound,  it  rapidly  brings  on  vomiting,  convulsions,  and  death. 
Antiarin  contains  Ci4H,j)05. 

PiCROToxiN. — It  is  to  this  substance  that  Cocculus  indicus  owes  its  active 
properties.  Picrotoxin  forms  small,  colourless,  stellated  needles,  of  inex 
pressibly  bitter  taste,  which  dissolve  in  25  parts  of  boiling  ale  ^hol.  It  con- 
tains C,(^H604. 

AsPARAGiN. — This,  and  the  two  following,  are  azotized  bodies.  Asparagin 
is  found  in  the  root  of  the  marsh-mallow,  in  asparagus  sprouts,  and  in  several 
other  plants.  The  mallow-roots  are  chopped  small,  and  macerated  in  the  cold 
with  milk  of  lime  ;  the  filtered  liquid  is  precipitated  by  carbonate  of  ammonia, 
and  the  clear  solution  evaporated  in  a  water-bath  to  a  syrupy  state.  The 
impure  asparagin,  which  separates  after  a  few  days,  is  purified  by  re-crys- 
tallization. Asparagin  forms  brilliant,  transparent,  colourless  crystals, 
which  have  a  faint  cooling  taste,  and  are  freely  soluble  in  water,  especially 
when  hot.  When  dissolved  in  a  saccharine  liquid,  which  is  afterwards  made 
to  ferment,  when  heated  with  water  under  pressure  in  a  close  vessel,  or  when 
boiled  with  an  acid  or  an  alkali,  it  is  converted  into  ammonia  and  a  new  acid, 
the  aspartic,  Asparagin  contains  CgHgNgOg,  and  aspartic  acid  CgH^NOg.  The 
remarkable  relation  in  which  these  substances  stand  to  malic  acid  has  been 
already  noticed  under  the  head  of  malic  acid  (see  p.  415). 

Santonin. — This  substance  is  the  crystalline  principle  of  several  varieties 
of  Artemisia.  In  order  to  obtain  it,  the  seeds  are  crushed,  and  digested 
with  lime  and  spirit  of  wine,  when  a  yellow  liquid  is  obtained,  from  which 
the  alcohol  is"  separated  by  distillation.  The  residuary  liquid  is  saturated 
with  acetic  acid,  when  the  santonin  crystallizes.  This  substance  is  easily 
soluble  in  water  and  alcohol,  and  contains  Ca^jHigOg.  Santonin  possesses  the 
character  of  a  weak  acid. 


ORGANIC    BASES    OP    ARTIFICIAL    ORIGIN.  453 


ORGANIC    BASES    OF   ARTIFICIAL   ORIGIN. 

The  constitution  of  the  alkaloids,  which  occur  ready  formed  in  nature, 
is  not  yet  clearly  understood.  The  fact  that  all  these  substances  contain 
nitrogen, — the  alkaline  reaction,  which  the  greater  part  of  them  exhibits 
"With  vegetable  colours,  and  especially  their  faculty  of  combining  with  acids 
to  crystallizable  salts,  establish  an  obvious  relation  between  the  alkaloids 
and  ammonia.  This  has  never  been  doubted,  and  the  views  of  chemists 
have  been  divided  only  as  to  the  form  of  this  relation.  At  a  certain  time 
Berzelius  assumed  that  all  the  alkaloids  contained  ammonia  ready  formed, 
and  that  their  basic  properties  were  due  to  this  ammonia.  According  to 
this  view  the  formulae  of  quinine  and  morphine  would  be — 

Quinine  CjoH,2N02=C2oH9  02,NH3 

Morphine C34Hi9N06=C34Hie06,NH3. 

This  view,  in  the  general  form  in  which  it  was  proposed,  is  certainly  inad- 
missible. It  is  supported  by  very  scanty  experimental  evidence,  and  was 
never  universally  adopted.  There  may  be  some  alkaloids  so  constituted  as 
represented  by  the  theory  of  Berzelius.  There  are,  however,  a  great  many, 
the  constitution  of  which  is  obviously  different.  Several  of  these  substances 
have  been  lately  the  subject  of  extensive  and  careful  inquiries;  but  these 
researches,  although  they  have  established  their  formulae  and  increased  our 
knowledge  regarding  their  salts,  have  as  yet  elicited  but  few  facts  which 
promise  to  afford  a  clearer  insight  into  the  nature  of  these  bodies. 

On  the  other  hand,  the  labours  of  the  last  ten  years  have  brought  to  light 
a  very  numerous  group  of  substances  perfectly  analogous  to  the  alkaloids 
which  are  found  in  plants,  but  produced  by  artificial  processes  in  the  labo- 
ratory. These  bodies,  which  are  termed  artificial  alkaloids  or  artificial  or- 
ganic bases,  are  mostly  volatile.  Their  constitution  is  much  simpler  than 
that  of  the  native  bases.  The  very  processes  which  give  rise  to  their  forma- 
tion often  permit  a  very  clear  insight  into  the  mode  in  which  the  elements 
are  grouped,  and  in  the  relation  existing  between  these  substances  and  am- 
monia. 

In  a  former  section  of  this  volume  (page  232),  it  has  been  stated  that  the 
majority  of  chemists  incline  to  assume  in  the  ammoniacal  salts  the  existence 
of  a  compound  metal  ammonium  NH^, 

Chloride  of  ammonium,  NH^Cl 
Sulphate  of  ammonia,     NH^OjSOj. 

Now,  recent  researches  have  shown,  that  in  these  salts,  1,  2,  3,  or  even  the 
4  eq.  of  hydrogen  may  be  replaced  by  compound  radicals,  containing  vari- 
able proportions  of  carbon  and  hydrogen,  without  any  change  in  their  fun- 
damental properties.  It  is  evident  that  we  obtain  in  this  manner,  in  addi- 
tion to  the  ammoniacal  salts,  four  new  series  of  compounds  very  ciosely 
allied  to  the  former.  Let  A  B  C  D  represent  a  series  of  such  radicals  capablo 
of  replacing  hydrogen,  then  the  following  series  of  salts  may  be  brmed «  - 


Ammonia-salts N 


First  group  of  compound 
ammonia-salts 


454      ORGANIC    BASES    OP    ARTIFICIAL    ORIGIN 


Second    group    of   com- 
pound ammonia-salts 


Third  group  of  compound 
ammonia-salts 


Fourth    group    of    com-  lyrjBlp,  NJ^lnqo 

pound  ammonia-salts      ^\c  f^^ ^^  C  r^'^^s- 

It  need  scarcely  be  mentioned  that  it  is  by  no  means  necessary  that  the 
Beveral  hydrogen-equivalents  in  ammonia  should  be  replaced  by  different 
radicals,  as  assumed  in  the  preceding  table.     Substances  of  the  formulae — 


are  even  more  easily  prepared  and  more  frequently  met  with. 

This  synopsis  shows  that  the  number  of  salts  capable  of  being  derived  from 
the  ordinary  ammoniacal  salts,  must  be  very  considerable.  Even  now  a  very 
extensive  series  has  been  prepared,  although  the  number  of  radicals  at  our 
disposal  at  present  is  still  comparatively  limited. 

It  has  been  mentioned  that  all  attempts  at  isolating  both  ammonium  and 
its  oxides  have  hitherto  failed  (see  page  232).  On  treating  chloride  of  am- 
monium or  sulphate  of  ammonia  with  mineral  oxides,  such  as  potassa,  lime, 
and  baryta,  decomposition  ensues,  chloride  of  potassium  or  sulphate  of  po- 
tassa, &c.,  is  formed,  and  the  separated  oxide  of  ammonium  splits  into 
ammonia-gas  and  water,  NH^OrsNHg-f-HO  (see  page  162). 

The  compound  ammonia-salts  are  likewise  decomposed  by  mineral  oxides. 
"With  the  three  first  classes  the  change  is  perfectly  analogous  to  that  of  am- 
moniacal salts,  the  separated  oxide  is  decomposed  into  water  and  a  volatile 
base,  the  properties  of  which,  according  to  the  nature  of  the  replacing  radi- 
cals, are  more  or  less  closely  approximated  to  those  of  ammonia  itself.  We 
arrive  in  this  manner  at  three  groups  of  organic  bases,  differing  from  one 
Another  by  the  amount  of  hydrogen  which  is  replaced  ;  they  have  been  dis- 
tinguished by  the  terms  amidoffen-,  imidoffen-,  and  nitrile-bases. 
fH  (-A  fA  (A 

(h  U  [h  Ic 


Ammonia.         Amidogen-         Imidogen-      Nitrile-bases. 

bases. 


The  last  group  of  ammoniacal  salts,  in  which  the  4  eq.  of  hydrogen  are 
replaced  by  radicals,  differ  in  their  deportment  from  the  former  classes. 
TPhese  salts  are  not  decomposed  by  potassa,  but  yield,  by  appropriate  treat- 
went,  a  series  of  substances  of  a  very  powerfully  alkaline  character,  which 
tre  expressed  by  the  general  formuloe  : — 


ill'' 


N^  ^  VO,  HO, 


ORGANIC    BASES    aP    ARTIFICIAL    ORIGIN.       455 

are  evidently  analogous  to  hydrated  oxide  of  ammonium ;  from  which  they 
differ,  however,  in  a  remarkable  manner,  by  their  powerful  stability. 

These  general  statements  will  become  more  intelligible  if  we  elucidate  them 
by  the  description  of  several  individual  substances ;  the  limits  of  this  work 
compel  us,  however,  to  confine  ourselves  to  the  more  important  members  of 
this  already  very  numerous  group,  which  is  moreover  daily  increasing. 

It  may  at  once  be  stated  that  by  far  the  greater  number  of  these  compounds 
are  derived  from  the  alcohols  or  substances  analogous  to  them,  and  that  the 
radicals  which  in  the  preceding  sketch  have  been  designated  by  the  letters 
A,  B,  C,  and  D,  are  chiefly  the  hydrocarbons  previously  described  under  the 
names  ethyl,  methyl,  and  amyl. 

BASES    OF   THE   ETHYL-SERIES. 

Ethyla»»inb,  Ethyl-ammonia,  C4H,jN=(H2,C4H5)=N(H2Ae). — On  digest- 
ing bromide  or  iodide  of  ethyl  (see  page  353)  with  an  alcoholic  solution  of 
ammonia,  the  alkaline  reaction  of  the  ammonia  gradually  disappears.  On 
evaporating  the  solution  on  the  water-bath  a  white  crystalline  mass  is 
obtained,  which  consists  chiefly  of  bromide  of  ethyl-ammonium,  Ael-f-NHg 
=N(H3Ae)I.  On  distilling  this  salt  in  a  retort  provided  with  a  good  con- 
denser, with  caustic  lime,  the  ethylamine  is  liberated  and  distils  over, 

NHjAel-f  K0= N(H2Ae)  +  HO-f  KI. 

Another  method  of  preparing  this  compound,  and  indeed  the  method  by 
which  this  remarkable  substance  was  first  obtained  by  M.  Wurtz,  consists  in 
submitting  cyanate  of  ethyl  to  the  action  of  hydrate  of  potassa.  In  describ- 
ing cyanic  acid  (see  page  426),  the  interesting  change  has  been  mentioned, 
which  this  substance  undergoes  when  treated  with  boiling  solution  of  potassa. 
In  this  case  cyanic  acid  splits  into  2  eq.  of  carbonic  acid  and  1  eq,  of  am- 
monia; cyanate  of  ethyl  (see  page  428)  sufi'ers  a  perfectly  analogous  decom- 
position, and  instead  of  ammonia  we  obtain  ethylamine. 

C2N0,H0-f2(K0,H0)=:2(K0,C0i)-fNH3 

Hydrated 
cyanic  acid. 

C2N0,Ae0+2(K0,H0)=2(K0,C02).fN(H2Ae) 

Cyanate  of  Ethylamine. 

ethyl. 

Cyanur.*te  of  ethyl,  isomeric  with  the  cyanate,  likewise  furnishes  ethylamine. 

Ethylamine  is  a  very  mobile  liquid  of  0-6964  sp.  gr.,  at  46°-4  (8°C),  which 
boils  at  64° -4  (18°C).  The  sp.  gr.  of  the  vapour  is  1-57.  It  has  a  most 
powerfully  ammoniacal  odour,  and  restores  the  blue  colour  to  reddened 
litmus  paper.  It  produces  white  clouds,  with  hydrochloric  acid,  and  is 
absorbed  by  water  with  great  avidity.  With  the  acids  it  forms  a  series  of 
neutral  crystallizable  salts  perfectly  analogous  to  those  of  ammonium. 

This  substance  imitates,  moreover,  in  a  remarkable  manner,  the  deport- 
ment of  ammonia  with  metallic  salts.  It  precipitates  the  salts  of  magnesia, 
alumina,  iron,  manganese,  bismuth,  chromium,  uranium,  tin,  lead,  and  mer- 
cury. Zinc-salts  yield  a  white  precipitate  which  is  soluble  in  excess.  Like 
ammonia,  ethylamine  dissolves  chloride  of  silver,  and  yields  with  copper- 
salts  a  blue  precipitate,  which  is  soluble  in  an  excess  of  ethylamine.  On 
adding  ethylamine  to  oxalic  ether,  a  white  precipitate  of  ethijl-ozamide. 
N(IIAe),C202,  is  produced  ;  even  a  compound  analogous  to  oxamic  acid  (see 
page  343)  has  been  obtained.     Ethylamine  may,  however,  be  readily  distin- 


456      ORGANIC    BASES    OF    ARTIFICIAL    ORIGIN. 

guished  from  ammonia ;  its  vapour  is  inflammable,  and  it  produces,  with 
bichloride  of  platinum,  a  salt  N(El3Ae)Cl,PtCl2,  crystallizing  in  golden  scales, 
which  are  rather  soluble  in  water.  If  ethylamine  is  treated  with  chlorine, 
it  furnishes  chloride  of  ethyl-ammonium  and  a  yellow  liquid  of  a  penetrating 
odour  exciting  tears,  which  contains  NClgAe.  This  substance  is  bichlor ethyl- 
amine. When  treated  with  potassa  it  is  converted  into  ammonia,  acetate  of 
potassa,  and  chloride  of  potassium,  NCl2,C4H5-j-3KO-f  HO=KO,C4H3034- 
NH3+2KCl. 

Ethylamine-urea.  On  passing  into  a  solution  of  ethylamine,  the  vapour  of 
hydrated  cyanic  acid,  the  liquid  becomes  hot,  and  deposits  after  evaporation, 
fine  crystals  of  ethylamine-urea,  C4H7N-f-C2NO,HO=C6H8N202=C2(H3,C4 
H5)N202=C2(Il3Ae)N202.  This  substance,  which  may  be  received  as  ordinary 
urea  (see  page  436),  in  which  1  eq.  of  hydrogen  is  replaced  by  ethyl,  may 
be  prepared  also  by  treating  cyanic  ether  with  ammonia,  C4H50,C2NO-f-NH3 
z^CgHgNaOj.  Ethylamine  urea  is  very  soluble  in  water  and  alcohol;  the 
concentrated  aqueous  solution,  unlike  that  of  ordinary  urea,  yields  no  pre- 
cipitate with  nitric  acid ;  but  on  gently  evaporating  the  mixture,  a  very 
soluble  crystalline  nitrate  of  ethylamine-urea  is  obtained.  Boiled  with  po- 
tassa, this  substance  yields  a  mixture  of  equal  equivalents  of  ammonia  and 
ethylamine,  C2(H3Ae)N202  -f  2(KO,UO)=2(KO,C02)  -f  NHg  -f  N(n2Ae).^ 

BiKTiiYLAMiNE,  Bicthyl^ ammonia,  C8HjjN  =  NH,2C4H5=N(HAe2). — A  mix- 
ture of  solution  of  ethylamine  and  bromide  of  ethyl,  heated  in  a  sealed  tube 
for  several  hours,  solidifies  to  a  crystalline  mass  of  bromide  of  biethyl- 
ammonium,  N(H2Ae)-|-AeBr=N(H2Ae2)Br.  The  bromide,  when  distilled 
with  potassa,  furnishes  a  colourless  liquid,  still  very  alkaline,  and  soluble  in 
water,  but  less  so  than  ethylamine.  This  compound  boils  at  133°  (65°C). 
It  forms  beautifully  crystallizable  salts  with  acids.  A  solution  of  chloride 
of  biethyl-ammonium  furnishes  with  bichloride  of  platinum,  a  very  soluble 
double  salt,  N(H2Ae2)Cl,rtCl2,  crystallizing  in  orange-red  grains,  very  diffe- 
rent from  the  orange-yellow  leaves  of  the  corresponding  ethyl-ammonium- 
ealts. 

Biethylamine-urea.  Biethylamine  probably  behaves  with  cyanic  acid  like 
ammonia  and  ethylamine,  giving  rise  to  biethylamine-urea.  This  substance 
has  been  produced  by  the  action  of  cyanic  ether  upon  ethylamine,  C4H5O, 
C2NO-fC4H7N  =  C,oHi2N202=C2(H22C4H6)N202=C2(H2Ae2)N202.  Biethyla- 
mine-urea is  very  crystallizable,  and  readily  forms  a  crystalline  nitrate. 
Boileu  with  potassa,  biethylamine-urea  yields  pure  ethylamine,  C2(H2Ae2)N2 
02+2(KO,HO)=2(KO,C02)-f2N(H2Ae). 

Triethylamine,  Triethyl-ammonia,  Cj2Hi5N=N3C4H6  =  NAe3. — The  for- 
mation of  this  body  is  perfectly  analogous  to  those  of  ethylamine  and  bie- 
thylamine. On  heating  for  a  short  time  a  mixture  of  biethylamine  with 
bromide  of  ethyl  in  a  sealed  glass  tube,  a  beautiful  fibrous  mass  of  bromide 
of  triethyl-ammonium  is  obtained,  from  which  the  triethylamine  is  sepa- 
rated by  potassa.  Triethylamine  is  a  colourless,  powerfully  alkaline  liquid, 
boiling  at  195°-8  (91°C).  The  salts  of  this  base  crystallize  remarkably  well. 
With  bichloride  of  platinum  it  forms  a  very  soluble  double  salt,  N(HAe3) 
Cl,PtCl2,  which  crystallizes  in  magnrficent  large  orange-red  rhombs. 

Hydrated  Oxide  of  Tetrethyl  -  ammonium,  C2oH2iN02  =  N4(C4H5)0,HO  = 
NAe40,H0. — When  anhydrous  triethylamine  is  mixed  with  dry  iodide  of 
ethyl,  a  powerful  reaction  ensues,  the  mixture  enters  into  ebullition,  and  so- 
lidifies on  cooling  to  a  white  crystalline  mass  of  iodide  of  tetrethyl-ammonium, 
NAcg  -|-  Ael  =  NAe4l.  The  new  iodide  is  readily  soluble  in  hot  water,  from 
which  it  crystallizes  on  cooling  in  beautiful  crystals  of  considerable  size.  This 
substance  is  not  decomposed  by  potassa ;  it  may  be  boiled  with  the  alkali  for 
hours  without  yielding  a  trace  of  volatile  base.  The  iodine  may,  however, 
be  readily  removed  by  treating  the  solution  with  silver-salts.     If  in  this  case 


OBQANIC    BASES    OF    ARTIFICIAL    ORIGIN.      457 

sulphate  or  nitrate  of  silver  be  employed,  we  obtain  together  with  iodide  of 
silver,  the  sulphate  or  nitrate  of  oxide  of  tetrethyl-ammonium,  which  crys- 
tallize on  evaporation ;  on  the  other  hand,  if  the  iodide  be  treated  with  freshly 
precipitated  protoxide  of  silver,  the  oxide  of  tetrethyl-ammonium  itself  is 
separated.  On  filtering  off  the  silver-precipitate,  a  clear  colourless  liquid  is 
obtained,  which  contains  the  isolated  base  in  solution.  It  is  of  a  strongly 
alkaline  reaction,  and  has  an  intensely  bitter  taste.  Solution  of  oxide  of 
tetrethyl-ammonium  has  a  remarkable  analogy  to  potassa  and  soda.  Like 
the  latter  substance,  it  destroys  the  epidermis  and  saponifies  fatty  substances 
with  formation  of  true  soaps.  With  the  salts  of  the  metals,  this  substance 
exhibits  exactly  the  same  reactions  as  potassa.  On  evaporating  a  solution 
of  the  base  in  vacuo,  long  slender  needles  are  deposited,  which  are  evidently 
the  hydrate  of  the  base,  with  an  additional  amount  of  water  of  crystallization. 
After  some  time  these  needles  disappear  again,  and  a  semi-solid  mass  is  left, 
which  is  the  hydrate  of  oxide  tetrethyl-ammonium.  A  concentrated  solution 
of  this  substance  in  water  may  be  boiled  without  decomposition,  but  on 
heating  the  dry  substance,  it  is  decomposed  into  pure  triethylamine  and 
olefiant  gas. 

NAe40,nO  =  2H0-f  NAe^  +  C4H4. 

Oxide  of  tetrethyl-ammonium  forms  neutral-salts  with  the  acids.  They 
are  mostly  very  soluble ;  several  yield  beautiful  crystals.  The  platinum 
salt,  NAe^CljPtClj,  forms  orange-yellow  octahedrons,  which  are  of  about  the 
same  solubility  as  the  corresponding  bichloride  of  platinum  and  potassium. 

Oxide  of  tetrethyl-ammonium  is  obviously  perfectly  analogous  to  the 
hitherto  hypothetical  oxide  of  ammonium.  It  is  a  compound  of  remarkable 
stability,  the  existence  and  properties  of  which  must  be  regarded  as  power- 
ful supports  of  the  ammonium-theory. 

BASES   OF   THE    METHTL-SEBIES. 

Methyiamine,  Methylammonia,  CjHgN  =  N(H„C2H5)  =  N(HjMe).  —  The 
formation  and  the  method  of  preparing  this  compound  from  the  cyanate  of 
methyl,  is  perfectly  analogous  to  those  of  ethylamine  (see  page  455)  ;  how- 
ever, methyiamine  being  a  gas  at  the  common  temperature,  it  is  necessary 
to  cool  the  receiver  by  a  freezing  mixture.  The  distillate,  which  is  an 
aqueous  solution  of  methyiamine,  is  saturated  with  hydrochloric  acid,  and 
evaporated  to  dryness.  The  crystalline  residue,  which  is  the  chloride  of 
methyl-ammonium,  when  distilled  with  dry  lime,  yields  methyiamine  gas, 
which,  like  ammonia  gas,  has  to  be  collected  over  mercury.  It  is  distin- 
guished from  ammonia,  by  a  slightly  fishy  odour,  and  by  the  facility  with 
which  it  burns.  Methyiamine  is  liquefied  about  32°  (0°C),  its  sp.  gr. 
is  1-08.  This  substance  is  the  most  soluble  of  all  gases,  at  53° -6  (12°C)  1 
volume  of  water  absorbs  1040  volumes  of  gas.  It  is  likewise  very  readily 
absorbed  by  charcoal.  In  its  chemical  deportment  with  acids  and  other 
substances,  methyiamine  resembles  in  every  respect  ammonia  and  ethyl- 
amine. Methyiamine  appears  to  be  produced  in  a  great  number  of  pro- 
cesses of  destructive  distillation ;  it  has  been  formed  by  distilling  several 
of  the  natural  organic  bases,  such  as  codeine,  morphine,  caffeine,  and 
several  others,  with  caustic  potassa ;  frequently  a  mixture  of  several  bases 
are  produced  in  this  manner. 

Among  the  numerous  derivatives  already  obtained  with  this  substance, 
methylamine-urea  C2(H3Me)N202,  and  himethylamine-urea  C2(H2Me2)N202,  and 
even  a  methyl-ethylamine-urea  C2(H2MeAe)N202  may  be  quoted.  The  latter 
substance  has  been  produced  by  the  action  of  cyanate  of  ethyl  upon  methyi- 
amine.    Even  a  series  of  platinnm-bages  analogous  to  those  produced  by  tiic 


468        ORGANIC    BASES    OF    ARTIFICIAL    ORIGIN. 

action  of  ammonia  upon  protochloride  of  platinum  (see  page  309),  have  been 
obtained  with  methylamine. 

BiMETHYLAMiNE  has  Hot  yct  been  prepared  in  a  pure  state. 

Trtmethylamine,  trimethyl-ammonia,  CgHgN  =  NSCgHg  =  NMeg.  —  This 
substance  is  readily  obtained  in  a  state  of  perfect  purity,  by  submitting 
oxide  of  tetramethyl-ammonium  (see  the  following  compound)  to  the  action 
of  heat.  It  is  gaseous  at  the  common  temperature,  but  liquefies  at  about 
48°-2  (90C)  to  a  mobile  fluid  of  very  powerfully  alkaline  reaction.  Tri- 
methylamine  produces  with  acids  very  soluble  salts.  The  platinum-salt 
N(HMe3)Cl,PtCl2,  is  likewise  very  soluble  and  crystallizes  in  splendid  orange- 
red  octahedrons.  According  to  Mr.  Winkles,  large  quantities  of  trimethyl- 
amine  are  found  in  the  liquor  in  which  salt  herrings  are  preserved. 

Hydrated  oxide  of  tetramethyl-ammonium,  CgHj3N02=N4C2H3,0, 
H0=NMe40,H0.  —  The  corresponding  iodide  may  be  obtained  by  adding 
iodide  of  methyl  to  the  preceding  compound.  Both  substances  unite  with  a 
sort  of  explosion.  The  same  iodide  is  prepared,  however,  with  less  diflB- 
culty,  simply  by  digesting  iodide  of  methyl  with  an  alcoholic  solution  of  am- 
monia. In  this  reaction,  a  mixture  of  the  iodides  of  ammonium,  methyl- 
ammonium,  bimethyl-ammonium,  trimethyl-ammonium,  and  tetramethyl- 
ammonium  is  produced.  The  first  and  last  compound  form  in  largest 
quantity,  and  may  be  separated  by  crystallization,  the  iodide  of  tetramethyl- 
ammonium  being  rather  difficultly  soluble  in  water.  From  the  iodide  the 
base  itself  is  separated  by  means  of  protoxide  of  silver.  The  properties 
are  similar  to  those  of  the  corresponding  ethyl-compound.  It  differs,  how- 
ever, from  oxide  of  tetrethyl-ammonium  in  its  behaviour  when  heated 
(see  page  467),  yielding  as  it  does  trimethylamine,  and  pure  methyl-alcohol, 
NMe40,HO==NMe3+MeO,HO. 

bases  of  the  amyl-sbries. 

The  formation  of  these  bodies  being  perfectly  analogous  to  that  of  the 
corresponding  terms  in  the  ethyl-series,  we  refer  to  the  more  copious  state- 
ment given  in  page  455,  and  confine  ourselves  to  a  brief  observation  of  their 
principal  properties. 

Amylamine,  amyl- ammonia,  C,oH,3N=N(H2,Cu)Hj,)=N(H2Ayl),  jsolour- 
less  liquid  of  a  peculiar  penetrating  aromatic  odour,  slightly  soluble  in 
water,  to  which  it  imparts  a  strongly  alkaline  reaction.  With  the  acids  it 
forms  crystalline  salts,  which  have  a  fatty  lustre.  Amylamine  boils  at 
199°-4  (93°C). 

An  amylamine-urea  has  been  prepared. 

Biamylakine,  biamyl-ammonia,  C2oH23N  =  N(H,2Cj(,H,i)=N(HAyl2),  aro- 
matic liquid,  less  soluble  in  water,  and  less  alkaline  than  amylamine.  It 
boi.s  at  about  338°  (170°C). 

Triamylamine,  triamyl-ammonia,  CgoHg3Ns=N3C,oH,,=NAyl3,  colourless 
liquid  of  properties  similar  to  those  of  the  two  preceding  bases,  but  boiling 
at  494°-6  (257°C).  The  salts  of  triamylamine  are  very  insoluble  in  water, 
and  fuse^  when  heated,  to  colourless  liquids,  floating  upon  water. 

Hydrated  oxide  of  tetramyl-ammonium,  C4oH45N02=N4C,(,H,,,0,HO 
ssrNAyl^OjHO.  —  This  substance  is  far  less  soluble  than  the  corresponding 
bases  of  the  methyl-  and  ethyl-series.  On  adding  potassa  to  the  aqueous 
solution  the  compound  separates  as  an  oily  layer.  On  evaporating  the 
solution  in  an  atmosphere  free  from  carbonic  acid,  the  alkali  may  be  ob- 
tained in  splendid  crystals  of  considerable  size.  When  submitted  to  distilla- 
tion it  splits  into  water,  triamylamine,  and  amylene  (see  page  390),  NAjlO, 
IU)==2HO-fNAylg+C,oH,o. 


ORGANIC    BASES    Of    ARTIFICIAL   OXIQIN.  459 


BASEa    OF    THE    PHENYL-SERIES. 

Aniline,  phenylamine,  CjjH^N  =  N(H2,Ci2H5)  =  N(H2Pyl).  —  Under  the 
head  of  salicylic  acid  (see  page  406,  and  also  page  399),  a  volatile  crystal- 
line substance  has  been  noticed  by  the  name  of  hydrated  oxide  of  phenyl.' 
This  substance,  of  which  a  fuller  description  is  given  in  Section  IX.,  imitates 
to  a  certain  extent  the  deportment  of  an  alcohol,  but  several  very  character- 
istic transformations  of  the  alcohols,  and  especially  the  conversion  into  the 
corresponding  acid,  have  not  as  yet  been  realized.  The  organic  base,  how- 
ever, which  is  derived  from  this  alcohol  in  the  same  manner  as  methylamine, 
ethylamine,  and  amylamine,  from  methyl-,  ethyl-,  and  amyl-alcohol,  is  known 
under  the  term  aniline,  a  name  given  to  it  on  account  of  its  relation  to  the 
indigo-series.  Aniline  cannot  be  produced  from  phenyl-alcohol  by  the  same 
processes  which  have  furnished  the  bases  of  the  other  alcohols,  neither  bro- 
mide nor  iodide  of  phenyl  having  as  yet  been  obtained.  However,  on  heating 
phenyl-alcohol  with  ammonia  in  sealed  tubes,  anUine  is  produced,  PylO,HO 
-j-NH3=2HO-j-N(HjPyl).  This  process,  however,  although  interesting  as 
establishing  clearly  the  relation  of  aniline  and  phenyl-alcohol,  is  not  calcu- 
luted  to  yield  large  quantities  of  this  substance.  Aniline  is  invariably 
obtained  either  from  indigo  or  from  nitrobenzol. 

Powdered  indigo  boiled  with  a  highly-concentrated  solution  of  hydrate  of 
potassa  dissolves  with  evolution  of  hydrogen  gas  to  a  brownish-red  liquid 
containing  a  peculiar  acid,  the  chrysanilic,  which  becomes  gradually  converted 
into  another  acid,  the  anthranilic  (see  page  474).  If  this  matter  be  trans- 
ferred to  a  retort  and  still  farther  heated,  it  swells  up  and  disengages  ani- 
line, which  condenses  in  the  form  of  oily  drops  in  the  neck  of  the  retort  and 
in  the  receiver.  Separated  from  the  ammoniacal  water  by  which  it  is  accom- 
panied, and  re-distilled,  it  is  obtained  nearly  colourless.  The  formation  of 
aniline  from  indigo  is  represented  by  the  following  equation  : — 

Ci6H5N02-f2(KO,HO)-f2HO=C,^H,N-f4(KO,C03)-J-4H. 

Indigo.  Aniline. 

In  order  to  prepare  aniline  from  nitrobenzol  (see  page  399),  this  substance 
is  submitted  to  a  process  discovered  by  Zinin,  which  has  proved  a  very  abun- 
dant source  of  artificial  organic  bases.  An  alcoholic  solution  of  nitro-benzol 
is  treated  with  ammonia  and  sulphuretted  hydrogen,  until  after  some  hours  a 
precipitate  of  sulphur  takes  place.  The  brown  liquid  is  now  saturated  again 
with  sulphuretted  hydrogen,  and  the  process  repeated  until  sulphur  is  no 
longer  separated.  The  reaction  may  be  remarkably  accelerated  by  occasion- 
ally heating  or  distilling  the  mixture.  The  liquid  is  then  mixed  with  excess 
of  acid,  filtered,  boiled  to  expel  alcohol  and  unaltered  nitrobenzol,  and  then 
distilled  with  excess  of  caustic  potassa.  The  transformation  of  nitrobenzoj 
into  aniline  is  represented  by  the  equation : — 

C^H6N04-f  6HS=C«H,N-|-  4H0+ 6S 

Nitrobenzol.  Aniline. 

If  the  aniline  be  required  quite  pure,  it  must  be  converted  into  oxalate,  the 
salt  several  times  crystallized  from  alcohol,  and  again  decomposed  by  hydrate 
of  potassa. 

Aniline  exists  among  the  products  of  the  distillation  of  coal,  and  probably 
of  other  organic  matters  ;  it  is  formed  in  the  distillation  of  anthranilic  acid 
(see  page  474),  and  occasionally  in  other  reactions. 

When  pure,  aniline  forms  a  thin,  oily,  colourless  liquid,  of  faint  vinous 


460      ORGANIC    BASES    OF    ARTIFICIAL    ORIGIN. 

odour,  and  aromatic,  burning  taste.  It  is  very  volatile,  but  nevertheless  has 
a  high  boiling-point,  369°'6  (182°C).  In  the  air  it  gradually  becomes  yellow 
or  brown,  and  acquires  a  resinous  consistence.  Its  density  is  1-028.  Water 
dissolves  aniline  to  a  certain  extent,  and  also  forms  with  it  a  kind  of  hydrate ; 
alcohol  and  ether  are  miscible  with  it  in  all  proportions.  It  is  destitute  of 
alkaline  reaction  to  test-paper,  but  is  quite  remarkable  for  the  number  and 
beauty  of  the  crystallizable  compounds  it  forms  with  acids.  Two  extraordi- 
nary reactions  characterize  this  body  and  distinguish  it  from  all  others,  viz., 
that  with  chromic  acid,  and  that  with  solution  of  hypochlorite  of  lime.  The 
former  gives  with  aniline  a  deep  greenish  or  bluish-black  precipitate,  and 
the  latter  an  extremely  beautiful  violet-coloured  compound,  the  fine  tint  of 
which  is,  however,  very  soon  destroyed. 

Substitution-products  of  aniline.  —  Under  the  head  of  indigo,  a  product  of 
oxidation  of  this  substance  will  be  noticed,  to  which  the  name  isatin  has 
been  given  (see  page  471).  When  isatin  is  distilled  with  an  exceedingly  con- 
centrated solution  of  caustic  potassa,  it  is,  like  indigo,  resolved  into  aniline, 
carbonic  acid,  and  free  hydrogen.  In  like  manner,  when  chlorisatin  or 
bichlorisatin,  two  chloro-substitutes  of  isatin,  are  similarly  treated,  they  yield 
products  analogous  to  aniline,  but  containing  one  or  two  equivalents  of  chlo- 
rine respectively  in  place  of  hydrogen.  The  chloraniline,  C,2(H8C1)N,  and 
bichlor aniline,  Ci,(H5Cl2)N,  thus  produced,  cannot  be  obtained  directly,  how- 
ever, from  aniline  by  the  action  of  chlorine,  thus  dififering  from  ordinary 
substitution-compounds ;  but  aniline  may  be  reproduced  from  them  by  the 
same  re-agent,  which  is  capable  of  reconverting  chloracetic  acid  into  ordi- 
nary acetic  acid,  namely,  an  amalgam  of  potassium  (see  page  375),  They  are 
the  first  cases  on  record  of  organic  bases  containing  chlorine. 

Chloraniline  forms  large,  colourless  octahedrons  having  exactly  the  odour 
and  taste  of  aniline,  very  volatile,  and  easily  fusible ;  it  distils  without  de- 
composition at  a  high  temperature,  and  burns,  when  strongly  heated,  with  a 
red  smoky  flame  with  greenish  border.  It  is  heavier  than  water,  indifferent 
to  vegetable  colours,  and,  except  in  being  solid  at  common  temperatures,  re- 
sembles aniline  in  the  closest  manner.  It  forms  numerous  and  beautiful 
crystallizable  salts.  If  aniline  be  treated  with  chlorine-gas,  the  action  goes 
farther,  trichloraniline,  Ci2(H4Cl3)N,  being  produced,  a  volatile  crystalline 
body  which  has  no  longer  any  basic  properties.  The  corresponding  bromine- 
compounds  have  also  been  formed  and  described. 

Nitraniline.  —  If  nitrobenzol  be  heated  with  fuming  nitric  acid,  or,  still 
better,  with  a  mixture  of  that  acid  and  oil  of  vitriol,  it  is  converted  into  a 
substance  called  binitrobenzol,  containing  C12H4N2O8,  or  nitrobenzol  in  which 
an  additional  equivalent  of  hydrogen  is  replaced  by  the  elements  of  hyponi- 
tric  acid  (see  page  399).  When  this  is  dissolved  in  alcohol  and  subjected  to 
the  reducing  action  of  sulphide  of  ammonium  in  Zinin's  process,  it  furnishes 
a  new  substance  of  basic  properties,  nitraniline,  having  the  constitution  of  a 
hyponitric  acid  substitution-product  of  ordinary  aniline.  The  attempts  to 
prepare  it  direct  from  aniline  by  means  of  nitric  acid  were  unsuccessful,  the 
principal  product  being  usually  carbazotic  acid.  Nitraniline  forms  yellow, 
acicular  crystals,  but  little  soluble  in  cold  water,  although  easily  dissolved 
by  alcohol  and  ether.  When  warmed  it  exhales  an  aromatic  odour,  and 
melts.  At  a  higher  temperature  it  distils  unchanged.  By  very  gentle  heat 
it  may  be  sublimed  without  fusion.  It  is  heavier  than  water,  does  not  aff"ect 
test-paper,  and  like  chlor-  and  bromaniline  fails  to  give  with  hypochlorite 
of  lime  the  characteristic  reaction  of  the  normal  compound.  Nitraniline 
forms  crystallizable  salts,  of  which  the  hydrochlorate  is  the  best  known. 
This  substance  contains  the  elements  of  aniline  with  an  equivalent  of  hy- 
drogen replaced  by  hyponitric  acid,  or  Cj2H6N204=Cj2(HgN04)N. 

Cyaniline  is  formed  by  the  action  of  cyanogen  upon  aniline ;  it  is  a  crys- 


ORGANIC   BASES   OF   ARTIFICIAL   ORIGIN.         461 

talline  substance  capable  of  combining  with  acids  like  aniline,  but  very  prone 
to  decomposition.  Cyaniline  contains  Ci4H7N,=Ci2H7NCy.  Hence  it  is 
formed  by  the  direct  union  of  1  eq.  of  cyanogen  and  1  eq.  of  aniline. 

Melaniline. — The  action  of  dry  chloride  of  cyanogen  upon  anhydrous  ani- 
line gives  rise  to  the  formation  of  a  resinous  substance,  which  is  the  chlo- 
rine-compound of  a  very  peculiar  basic  substance  to  which  the  name  me- 
laniline has  been  given.  Dissolved  in  water  and  mixed  with  potassa,  the 
above  salt  furnishes  melaniline  in  form  of  an  oil,  which  rapidly  solidifies  to 
a  beautiful  crystalline  mass.  Melaniline  contains  CagHiaNj.  The  following 
equation  represents  its  formation : — 

2CuH,N+CsjNCl==C26Hi4N3Cl. 

Melaniline,  when  treated  with  chlorine,  bromine,  iodine,  or  nitric  acid, 
yields  basic  substitution-products,  in  which  invariably  2  eq.  of  hydrogen  are 
displaced.     It  combines  with  2  eq.  of  cyanogen. 

The  constitution  of  the  substitution-products  of  aniline  is  readily  intelli- 
gible ;  it  is  evident  that  these  substances  owe  their  origin  to  a  double  sub- 
stitution, namely,  first,  of  1  equivalent  of  hydrogen  in  ammonia  by  phenyl; 
and,  secondly,  of  one  or  several  equivalents  of  hydrogen  in  phenyl  by 
chlorine,  bromine,  &c.  The  arrangement  of  the  elements  may  be  conveni- 
ently illustrated  by  the  following  formulae  : — 

Ammonia NH, 

Aniline NHj.CiaHj 

Chloraniline NH2,Ci2(H4Cl) 

Bromaniline  NH2,G,2(H4Br) 

Bibromaniline NH2,Ca(H3Br2) 

Tribromaniline NH2,Cj2(H2Br3) 

Nitraniline NH2,Ci2(H4NOJ 

The  constitution  of  cyaniline  and  melaniline  is  not  so  readily^  understood. 
Aniline-compounds  corresponding  to  the  amides  and  amidog en-acids,  &c.  —  In 
describing  the  ammonia-salts  of  various  acids,  attention  has  been  repeatedly 
called  to  the  power  possessed  by  many  of  them  to  yield  several  new  groups 
of  compounds  by  the  loss  of  a  certain  amount  of  water  (see  pages  3-43  and 
415).  These  groups  are  perhaps  best  elucidated  by  the  derivatives  of  oxalic 
acid- 

NH40,C203  —       2H0  =  CgOjNjH 

Neutral  oxalate  of  Oxamide. 

ammonia. 

NH^OAOa^HOCgOa      —        2H0  =         C202,NH2Cj03,HO 

Binoxalate  of  ammonia.  "^      Oxamic  acid. 

NH^CCjOj  —       4H0  =  CaN  j 

Neutral  oxalate  of  Oxalonitrile  or 

ammonia.  cyanogen. 

The  terms  corresponding  to  oxamide  and  oxamic  acid  have  also  been  ob- 
tained in  the  aniline-series  ;  they  are  produced  by  the  distillation  of  neutral 
and  acid  oxalate  of  aniline,  and  have  been  called  oxanilide  and  oxanilic  acid. 

Oxanilide  =     C,4H6N02     =     CjOa.NfHPyl) 

Oxanilic  acid    ==     CigHgNOg     =     C202,N(HPyl),C303,HO. 

Compounds  analogous  to  the  nitriles  have  not  been  obtained  in  the  aniline- 

39* 


462       ORGANIC    BASES    OF    ARTIFICIAL    ORIGIN. 

series,  and  the  reason  is  intelligible  if  we  glance  at  the  formula  of  oxalaf 
of  aniline,  N(H3Pyl)0,C203.     It  is  obvious  that  4  eq.  of  water  cannot  be 
eliminated  from  this  salt  without  touching  the  hydrogen  of  the  phenyl,  i.  e,, 
without  destroying  the  compound  altogether.     A  great  many  anilides  and 
anilic  acids  have  been  formed. 

Aniline-urea.  —  On  passing  the  vapour  of  cyanic  acid  into  aniline,  the  sub- 
stance becomes  hot,  and  solidifies  on  cooling  to  a  crystalline  mass,  containing 
Ci4H8N202=:C2(H3Pyl)N202.  This  is  the  composition  of  aniline-urea.  This 
substance,  however,  does  not  combine  with  acids  like  the  ureas  (see  pages 
427  and  456),  it  is  only  isomeric  with  the  true  aniline-urea,  which  is  obtained 
by  another  process.  Among  the  derivatives  of  benzoic-acid,  nitrobenzoic 
acid,  C,4(H4N04)03,H0,  (see  page  397,)  has  been  mentioned.  The  ether  of 
this  acid,  C4H50,Ci4(H4N 04)03,  like  oxalic  ether,  and  many  other  ethers, 
furnishes  an  amide  when  treated  with  ammonia.  This  substance,  niirohen- 
zamide,  C,4(H4N04)02,NH2,  under  the  influence  of  sulphide  of  ammonium, 
suffers  a  change,  which  is  perfectly  analogous  to  that  of  nitrobenzol  under 
similar  conditions  (see  page  459).  The  mixture  soon  deposits  sulphur,  and 
yields,  on  evaporation,  crystals  of  aniline-urea. 

Ci4H6N206-f-6HS     =    C,4H8N202+4HO-f6S 

Nitrobenzamide.  Aniline-urea. 

This  substance,  which  was  discovered  by  M.  Chancel,  combines  with  nitric 
and  hydrochloric  acid,  and  even  with  bichloride  of  platinum. 

Bases  homologous  to  Aniline. 
In  a  former  section  of  this  Manual  (page  403),  a  series  of  hydrocarbons 
has  been  mentioned,  which  are  homologous  to  benzol.  Each  of  these  sub- 
stances, when  treated  with  fuming  nitric  acid,  yields  a  nitro-substitute  coi-- 
responding  to  nitrobenzol,  which,  under  the  influence  of  sulphuretted  hydro- 
gen, is  converted  into  a  basic  compound  homologous  to  aniline.  We  thus 
obtain  the  following  group  : — 


Benzol, 

CijH  ftH 

Nitrobenzol, 

C,2H6N04 

Aniline, 

N(H2.C,2H5) 

Toluol, 

C14H.  .jH 

Nitrotoluol, 

C,4H  ,N04 

Toluidine, 

N(H2,C,4H,) 

Xylol, 

^16^  9H 

Nitroxylol, 

C,6H,N04 

Xylidine, 

N(H2,C,eH9) 

Cumol, 

CigHijH 

Nitrocumol, 

C.8HUNO4 

Cumidine, 

N(H2,C,8H„) 

Toluidine,  C,4H9N=N(H2,C,4H7)=N(H2Tyl).  —  This  is  prepared  exactly 
like  aniline. 

Toluidine  forms  colourless  platy  crystals,  very  sparingly  soluble  in  water, 
but  easily  in  alcohol,  ether,  and  oils ;  it  is  heavier  than  water,  has  an  aro- 
matic taste  and  odour,  and  a  very  feeble  alkaline  reaction.  At  104°  (40°C) 
it  melts,  and  at  388°  (198°C),  boils,  and  distils  unchanged ;  it  forms  a  series 
of  beautiful  crystallizable  salts. 

Xylidine,  C,6Hi,N=N(H2,C,6Hg)=N(H2Xyl).  — Of  this  compound  little 
more  than  the  existence  is  known. 

Cumidine,  C,8Hi3N=N(H2,C,8H„)=N(H2Cyl).  —  This  substance  is  an  oil 
which  boils  at  437°  (225°C).     It  forms  magnificent  salts  with  the  acids. 

The  following  two  bases  are  likewise  closely  allied  to  the  group  of  aniline- 
bases,  both  by  their  mode  of  formation  and  by  their  constitution. 

Naphthalidine,  C2oHaN=N(H2,C2oH7)=N(H2Nyl).  -^  This  substance  is 
interesting,  as  being  one  of  the  first  of  its  kind  produced  by  Zinin's  process. 

It  is  obtained  by  the  action  of  sulphide  of  ammonium  upon  an  alcoholic 
solution  of  nitronaphthalase,  one  of  the  numerous  products  of  the  action  of 
nitric  acid  upon  the  hydrocarbon  naphthalin,  which  will  be  noticed  in  the 
last  section  of  the  Manual.     When  pur«  it  forms  colourless  silky  needles, 


ORGANIC    BASES    OF   ARTIFICIAL  ORIGIN.        468 

fu3lble,  and  volatile  without' decomposition.  It  has  a  powerful,  not  disagree- 
able odour  and  burning  taste,  is  nearly  insoluble  in  water,  but  readily  dis- 
solves in  alcohol  and  ether ;  the  solution  has  no  alkaline  reaction.  Naph- 
thalidine  forms  numerous  crystallizable  salts. 

Chloronicine,  C,o(H6C1)N=NH2C,o(H4C1).  —  a  substance  of  the  above 
composition  has  been  lately  discovered  by  Saint  Evre,  and  deserves  special 
notice,  because  it  may  be  viewed  as  a  chloro-substitute.  of  the  natural 
alkaloid  nicotine  (see  page  450),  which  contains  CjoH^N.  It  is  obtained  by 
the  following  rather  complicated  series  of  reactions.  A  stream  of  chlorine 
is  passed  through  a  solution  of  benzoate  of  potassa  to  which  some  free 
alkali  has  been  added,  when  a  deposit  forms  consisting  of  chlorate  of  potassa 
and  the  potassa-salt  of  a  new  chlorinetted  acid  Ci2(H4Cl)03,HO.  This  acid, 
which  is  derived  from  benzoic  acid  by  the  removal  of  2  eq.  of  carbon  in  the 
form  of  carbonic  acid  and  by  the  introduction  of  1  eq.  of  chlorine  in  the 
place  of  1  eq.  of  hydrogen,  has  received  the  name  of  chloroniceic  acid.  It 
forms  cauliflower-like  crystals,  fusible  at  302°  (ISO^C),  and  boiling  at  419° 
(215°C).  It  is  volatile  without  decomposition  ;  when  submitted  to  distilla- 
tion with  lime  it  yields  a  chlorinetted  hydrocarbon  chloronicene  CjoCHjCl), 
which  is  converted  into  nitrochloronicene  Ciq,(H4C1N04)  by  the  action  of 
fuming  nitric  acid.  This,  lastly,  when  treated  with  sulphide  of  ammonium 
furnishes  chloronicine.  It  forms  brown  flakes,  which  dissolve  in  a  great  deal 
of  water ;  the  solution,  however,  has  no  alkaline  reaction.  It  forms  crys- 
tallizable salts  with  hydrochloric  and  acetic  acids,  and  a  fine  platinum-salt. 
The  perfect  analogy  in  the  derivatives  from  chloroniceic  acid  to  that  of 
aniline  and  benzoic  acid,  is  obvious  from  the  following  table : — 

Benzoic  acid  C,4Hg04  Chloroniceic  acid  Ci2(HgCl)04 

Benzol  CigHg  Chloronicene  ^loi^s,^^) 

Nitrobenzol    C,2(H5N04)  Nitrochloronicene  Cio(H4ClN04) 

Aniline  Ci2H5,H2N  Chloronicine  C,o(H4Cl)H2N. 

Up  to  the  present  moment  chloronicine  has  not  yet  been  converted  into 
nicotine,  nor  has  nicotine  been  transformed  into  chloronicine. 

MIXED    BASES. 

In  one  of  the  preceding  paragraphs  it  has  been  mentioned  that  the  several 
hydrogen-equivalents  in  ammonium  may  be  replaced  by  different  hydro-carbon 
radicals.  In  fact,  on  treating  aniline  or  toluidine  with  bromide,  or  iodide  of 
ethyl,  as  described  under  the  head  of  ethylamine,  the  following  series  of 
compounds  are  obtained : 

Aniline  N(H2Pyl)  Toluidine  N(H2Tyl) 

Ethylauiline  N(HPylAe)  Ethylotoluidine     N(HTylAe) 

Biethylaniline       N(PylAe2)  Biethylotoluidine  N(TylAe2) 

Ammonium  base  N(PylAe3)0,H0  Ammonium-base'  N(TylAe3)0,H0 

Ethylaniline  (ethylophenylamine)  and  biethylaniline  (biethylopheny- 
lamine)  are  liquids  greatly  resembling  aniline.  They  boil  respectively  at 
399°-2  (204OC)  and  416° -5  (213°-5C).  The  ammonium-base,  to  which  the 
name  Oxide  of  biethylophenyl-ammonium  may  be  given,  is  soluble  in  water, 
with  a  powerful  alkaline  reaction,  corresponding  in  its  general  properties  to 
oxide  of  tetrethyl-ammonium  (see  page  456).  The  series  of  bases  which 
may  be  possibly  obtained  by  changing  the  radicals  is  almost  without  limit ; 
even  now  a  considerable  variety  has  been  produced,  of  which  however  only 

*  Unpublished  researches  of  Messrs  B.  Morley  and  John  Abel, 


464  BASES    OF    UNCERTAIN    CONSTITUTION. 

a  few  will  be  mentioned  here,  as  remarkable  for  the  diversity  of  the  materials 
with  which  they  are  constructed. 

HyDRA.TED    OXIDE    OF    TRIETHYLAMYL-AMMONIUM,     CggHgyNOj  =  N(3C4H5, 

CioHj,)0,HO  =  N(Ae3Ayl)0,HO.  Triethylamine  (see  page  456),  when  boiled 
with  iodide  of  amyl  is  slowly  converted  into  a  crystalline  mass  of  iodide  of 
Triethylamyl- ammonium.  The  base  liberated  with  protoxide  of  silver  and 
submitted  to  distillation  yields  olefiant  gas,  and 

BiETHYLAMiNE,  Ci8H2iN=  N(2C4H5,C,oH,i)  =  N(Ae2Ayl),  a  liquid  boiling 
at  309°-2  (154°C).  This  compound  is  most  powerfully  attacked  by  iodide 
of  methyl.  Both  substances  immediately  solidify  to  a  beautifully  crystalline 
iodide  from  which  protoxide  of  silver  separates. 

Hydbated  oxide  of  methylo-biethylamyl-ammonium,  C2oH25N02=N 
(C2H3,2C4H5,CioHjj)0,HO=N(MeAe2Ayl),0,HO.  This  substance,  which  is 
a  powerfully  alkaline  base,  soluble  in  water,  when  distilled  undergoes  the 
same  decomposition  as  the  other  members  of  the  fourth  group  of  bases, 
yielding  _olefiant  gas,  and 

Methylethylamylamine,  or  ammonia,  in  which  1  eq.  of  hydrogen  is 
replaced  by  methyl,  another  by  ethyl,  and  a  third  by  amyl,  C,6H,9N  =  N(C2 
H3,C4H5,C,oHii)==N(MeAeAyl).  This  is  a  basic  oil. of  a  peculiar  aromatic 
odour,  boiling  at  275°  (135°C)  and  forming  crystallizable  salt  with  the  acids. 
Ethylamylaniline,  C26H21N  =  N(C]2H5,C4H5,C,oHjj)  =  N(PylAeAyl).— 
Ethylaniline  (see  page  463)  treated  with  iodide  of  amyl  yields  the  iodide 
of  the  above  base,  which  is  separated  by  distillation  with  potassa.  It  is  an 
aromatic  oil,  boiling  at  503°-5  (262°C).  The  action  of  iodide  of  methyl  upon 
this  substance  gives  rise  to  a  new  iodide  from  which  protoxide  of  silver  sepa- 
rates, and 

HyDRATED  oxide   op   METHYL-ETHYL-AMYLO-PHENYL-AMMONIUM,  CggHggNOj 

^  N(C2FT3,C4H5,C,oH„,C,2H5)0,HO  =  N(MeAeAylPyl)0,HO.  This  compound 
IS  very  soluble  in  water,  is  powerfully  alkaline,  and  of  an  extremely  bitter 
taste.  The  composition,  established  by  the  examination  of  a  platinum-salt, 
is  certainly  remarkable,  for  this  compound  contains  the  radicals  of  not  less 
than  four  different  alcohols. 


BASES    OF   UNCERTAIN    CONSTITUTION 


In  addition  to  the  artificial  bases  which  have  just  been  described,  several 
others  have  been  formed  by  processes  less  simple  and  less  calculated  to  afford 
a  clear  insight  into  their  constitution.  The  destructive  distillation  of  nitro- 
genous substances  has  furnished  a  rich  harvest  of  similar  substances.  A  few 
of  the  most  interesting  may  be  briefly  mentioned. 

Chinoleine  (Leucoline)  CjgHgN.  —  Quinine,  cinchonine,  strychnine,  and 
probably  other  bodies  of  this  class,  when  distilled  with  a  very  concentrated 
solution  of  potassa,  yield  an  oily  product  resembling  aniline  in  many  respects, 
and  possessing  strong  basic  powers ;  it  is,  however,  less  volatile  than  that 
substance,  and  boils  at  460°  (235°C).  When  pure  it  is  colourless  and  has  a 
faint  odour  of  bitter  almonds.  Its  density  is  1-081.  It  is  slightly  soluble  in 
water,  and  miscible  in  all  proportions  with  alcohol,  ether,  and  essential  oils. 
Chinoleine  has  no  alkaline  reaction,  but  forms  salts  with  acids,  which,  gene~ 
rally  speaking,  do  not  crystallize  very  freely. 


BASES     OP    UNCERTAIN     CONSTITUTION.  465 

Bases  from  Coal-tar  Oil. 

Ktanol  and  leukol.  —  The  volatile  basic  bodies  described  under  these 
names  have  lately  been  identified,  the  first  with  aniline  and  the  second  with 
chinoleine.  They  are  separated  from  the  coal-oil  by  agitating  large  quanti- 
ties of  that  liquid  with  hydrochloric  or  diluted  sulphuric  acid,  and  then  dis- 
tilling the  acid  liquid  with  excess  of  potassa  or  lime.  They  are  readily  sepa- 
rated by  distillation. 

PicoLiNE  CjaHp^N. — Dr.  Anderson  has  described  under  the  foregoing  name 
a  third  volatile,  oily  base,  present  in  certain  varieties  of  coal-tar-naphtha, 
being  there  associated  with  aniline,  chinoleine,  and  several  other  volatile  sub- 
stances but  imperfectly  understood.  It  is  separated  without  difficulty  from 
the  two  bases  mentioned  by  distillation,  in  virtue  of  its  superior  volatility. 
Picoline,  when  pure,  is  a  colourless,  transparent,  limpid  liquid,  of  powerful 
and  persistent  odour,  and  acrid,  bitter  taste.  It  is  unaflFected  by  a  cold  of  0° 
( — 17°-7C).  It  is  extremely  volatile,  evaporates  rapidly  in  the  air,  and  does 
not  become  brown  like  aniline  when  kept  in  an  ill-stopped  bottle.  Picoline 
has  a  sp.  gr.  of  0-955,  and  boils  at  272°  (133° -SC).  It  mixes  in  all  propor- 
tions with  pure  water,  but  is  insoluble  in  caustic  potassa  and  most  saline 
solutions.  The  alkalinity  of  this  substance  is  exceedingly  well  marked ;  it 
restores  the  blue  cblour  of  reddened  litmus,  and  forms  a  series  of  crystalliza- 
ble  salts.  This  substance,  as  seen  from  the  above  formula,  is  isomeric  with 
aniline,  but  numerous  characteristic  reactions  completely  distinguish  it  from 
this  body. 

Bases  from  Animal  Oil. 

The  oily  liquid  obtained  by  the  distillation  of  bones  and  animal  matter 
generally,  frequently  designated  by  the  term  Dippel's  oil,  contains  several 
volatile  organic  bases.  Together  with  some  of  the  substances  already  de- 
scribed, such  as  methylamine,  ethylamine,  picoline,  and  analine,  Dr.  Ander- 
son has  found  in  it  a  peculiar  base. 

Petinine  CgHjiN. — The  properties  of  this  substance  are  very  analogous  to 
those  of  biethylamine,  and  triethylamine.  It  has  the  same  composition  as 
biethylamine,  but  differs  from  it  by  its  higher  boiling-point,  which  is  175° 
(79° -oC),  that  of  biethylamine  bein^  133°  (55°C)  (see  page  455).  Some 
chemists  are  inclined  to  explain  this  difference  by  assuming  that  petinine  is 
an  ammonia-base,  containing  the  radical  butyl,  which  was  mentioned  under 
the  head  of  valeric  acid  (see  page  392),  in  one  word  that  it  is  butylamine  N(H2, 
CgHg),  homologous  to  ethylamine.  This  assumption  may  be  correct,  but  is 
not  as  yet  supported  by  any  experimental  evidence. 

Bases  obtained  by  the  action  of  Ammonia  upon  Volatile  Oils. 

FuRFURiNE. — When  sulphuric  acid  diluted  with  an  equal  bulk  of  water  is 
carefully  mixed  with  twice  its  weight  of  wheat-bran,  and  the  adhesive  pasty 
mass  obtained  exposed  in  a  proper  vessel  to  the  action  of  a  current  of  steam 
which  is  afterwards  condensed  by  a  worm  or  refrigerator,  a  liquid  is  obtained 
which  holds  in  solution  a  peculiar  volatile  oil,  to  which  the  term  furfurole  has 
been  given.  By  re-distillation  several  times  repeated,  the  first  half  of  the 
liquid  only  being  collected,  the  furfurole  can  be  extracted  from  the  water, 
and  then  by  distillation  alone  obtained  in  a  state  of  purity.  It  has  a  pale 
yellow  colour,  and  a  fragrant  odour  like  that  of  oil  of  cassia ;  its  specific 
gravity  is  1-165,  and  it  boils  at  325°  (162°-8C),  distilling  unchanged.  It  dis- 
solves in  all  proportions  in  alcohol  and  to  a  very  considerable  extent  in  water, 
and  is  readily  destroyed  by  strong  acids  and  caustic  alkalis,  especially  when 
aided  by  heat.  Furfurole  contains  CgHjOj.  The  specific  gravity  of  its  vapour 
is  3-493. 


466  BASES    OF    UNCERTAIN     CONSTITUTION. 

The  product  of  furfurole  is  very  greatly  increased  and  the  operation  much 
facilitated  by  previously  depriving  the  bran  of  all  starch,  glutin,  and  soluble 
matter  by  steeping  it  in  a  cold  dilute  solution  of  caustic  potassa,  and  wash- 
ing and  drying  by  gentle  heat  or  in  the  sun.  Maceration  in  cold  water  for 
some  time  answers  the  same  purpose,  owing  to  the  lactic  acid  formed  in  that 
case. 

In  contact  with  solution  of  ammonia,  furfurole  becomes  converted  in  the 
space  of  a  few  hours  into  a  yellowish-white,  crystalline,  insoluble  substance, 
furfurolamide,  G^^l^O^ ;  this  body  is  slowly  decomposed  in  contact  with 
water,  and  instantly  by  an  acid  into  ammonia  and  furfurole.  It  may  be  crys- 
tallized from  alcohol,  however,  in  which  it  dissolves  without  much  change. 
When  boiled  with  a  somewhat  dilute  solution  of  caustic  potassa,  no  ammonia 
is  disengaged,  but  the  substance  is  slowly  dissolved  if  the  quantity  of  liquid 
be  considerable,  and  the  solution  deposits  on  cooling  small,  white,  silky 
needles  of  a  substance  having  the  same  composition  as  furfurolamide  itself. 
There  is  no  other  product.  This  new  body,  to  which  the  name  furf urine  has 
been  given,  is  a  powerful  organic  base,  forming  with  acids,  a  series  of  beau- 
tiful crystallizable  salts,  and  decomposing  at  a  boiling  heat  the  saline  com- 
pounds of  ammonia.  Furfurine  is  very  sparingly  soluble  in  cold  water,  but 
dissolves  in  about  135  parts  at  212°  (100°C).  Alcohol  and  ether  dissolve  it 
freely ;  the  solutions  have  a  strong  alkaline  reaction.  It  melts  below  the 
boiling  point  of  water,  and  when  strongly  heated  inflames  and  burns  with  a 
red  and  smoky  light,  leaving  but  little  charcoal.  Its  salts  are  intensely 
bitter.     Furfurine  contains  in  1  equivalent  CsoH^gNjOg.* 

FucusiNE. — By  treating  several  varieties  of  fucus  with  sulphuric  acid  in 
exactly  the  same  manner  as  in  the  preparation  of  furfurole,  Dr.  Stenhouse 
obtained  a  series  of  substances,  which  he  designates  by  the  terms  fucusol, 
fucusamide,  and  fucusine.  They  have  exactly  the  same  composition  as  the 
corresponding  terms  in  the  furfurole-series,  and  also  most  of  their  properties, 
but  differ  in  some  details. 

Amarine  (benzoline). — The  hydrobenzamide  of  M.  Laurent,  C^jHigNg, 
produced  by  the  action  of  ammonia  on  pure  bitter-almond-oil  (see  page  400), 
when  long  boiled  with  a  solution  of  caustic  potassa,  suflFers  the  same  kind  of 
change  as  furfurolamide,  becoming  entirely  converted  into  a  new  body  iso- 
meric with  hydrobenzamide,  having  the  characters  of  a  salt-base,  and  to 
which  the  preceding  name  has  been  given.  Precipitated  by  ammonia  from 
a  cold  solution  of  the  hydrochlorate  or  sulphate,  amarine  separates  in  white 
curdy  masses,  which  when  washed  and  dried  become  greatly  reduced  in 
volume.  In  this  state  it  is  singularly  electric  by  friction  with  a  spatula.  It 
is  insoluble  in  water,  but  dissolves  abundantly  in  alcohol;  the  solution  is 
highly  alkaline  to  test-paper,  and  if  sufficiently  concentrated  deposits  the 
amarine  on  standing,  in  the  form  of  small,  colourless,  prismatic  crystals. 
Below  212°  (100°C)  it  melts,  and  on  cooling  assumes  a  glassy  or  resinous 
condition.  Strongly  heated  in  a  retort,  it  decomposes  with  production  of 
ammonia,  and  a  volatile  oil  not  yet  examined,  and  a  new  body,  pyi-obeiizolin, 
which  appears  to  be  a  neutral  substance,  insoluble  in  water,  dissolved  by 
boiling  alcohol,  and  containing  a  large  quantity  of  nitrogen.  It  is  fusible 
by  moderate  heat,  and  on  cooling  becomes  a  mass  of  colourless  radiating 
needles  or  plates.  The  salts  of  amarine  are  mostly  sparingly  soluble  ;  the 
sulphate,  nitrate,  and  hydrochlorate  are  crystallizable  and  very  definite. 
Amarine  contains  C42H,gN2. 

Thigsinnamijve. — The  volatile  oil  distilled  from  black  mustard-seed,  CgHj 
NSj,  which  will  be  noticed  farther  on,  in  contact  with  solution  of  ammonia, 

»  This  remarkable  substance,  the  nearest  approach  to  the  native  alkaloids  yet  made,  wa* 
diboorered  by  the  author  of  this  Manual. — Eds. 


BASES    OF    UNCERTAIN    CONSTITUTION.  467 

yields  a  compound  having  tKe  characters  of  an  organic  base,  and  forming 
colourless,  prismatic  crystals,  bitter  in  taste  and  soluble  in  water.  The 
solution  does  not  affect  test-paper.  It  melts  when  heated,  but  cannot  be 
sublimed.  Acids  combine  with  it,  but  form  no  crystallizable  salts:  the  double 
salts  of  the  hydrochlorate  with  bichloride  of  platinum  and  corrosive  subli- 
mate are  the  most  definite.  This  substance  contains  sulphur ;  its  formula  is 
CgHgNjSj.     It  is  the  only  product  of  the  action  of  ammonia  on  the  oil. 

Thiosinnamine  is  decomposed  by  metallic  oxides,  as  protoxide  of  lead, 
with  production  of  a  metallic  sulphide  and  a  new  body  of  basic  properties, 
free  from  sulphur,  called  sinnamine.  This  latter  substance  crystallizes  very 
slowly  from  a  concentrated  aqueous  solution  in  brilliant,  colourless  crystals 
which  contain  water.  It  has  a  powerful  bitter  taste,  is  strongly  alkaline  to 
test-paper,  and  decomposes  ammoniacal  salts  by  boiling.  With  the  excep- 
tion of  the  oxalate,  it  forms  no  crystallizable  salts.  Sinnamine  contains  in 
the  crystallized  state  CgHgNj.HO. 

When  mustard-oil  is  treated  with  protoxide  of  lead  or  baryta,  the  whole 
of  the  sulphur  is  withdrawn,  and  carbonic  acid  and  another  basic  substance 
produced,  which,  when  pure,  crystallizes  in  colourless  plates,  soluble  in  water 
and  in  alcohol ;  the  solution  has  a  distinct  alkaline  reaction.  Sinapoline,  the 
body  so  formed,  contains  C  uHjaNjOj. 

Bases  from  Aldehyde. 

Thialdine  — The  crystalline  compound  of  aldehyde  with  ammonia  (see 
page  369),  is  dissolved  in  12  te  16  parts  of  water,  mixed  with  a  few  drops  of 
caustic  ammonia,  and  then  the  whole  subjected  to  a  feeble  stream  of  sul- 
phuretted hydrogen.  After  a  time  the  liquid  becomes  turbid  and  deposits  a 
white  crystalline  substance,  which  is  the  body  in  question.  It  is  separated, 
washed,  dissolved  in  ether,  and  the  solution  mixed  with  alcohol  and  left  to 
evaporate  spontaneously,  by  which  means  the  base  is  obtained  in  large,  regu- 
lar, rhombic  crystals,  having  the  figure  of  those  of  common  gypsum.  The 
crystals  are  heavier  than  water,  transparent  and  colourless.  They  refract 
light  strongly.  The  substance  has  a  somewhat  aromatic  odour,  melts  at 
110°  (43°-3C),  and  volatilizes  slowly  at  common  temperatures.  It  distils 
unchanged  with  the  vapour  of  water,  but  decomposes  when  heated  alone.  It 
is  very  sparingly  soluble  in  water,  easily  in  alcohol  and  ether.  It  has  no 
action *on  vegetable  colours,  but  dissolves  freely  in  acids,  forming  crystalli- 
zable salts.  Heated  with  hydrate  of  lime  it  yields  chinoleine.  Thialdine 
contains  C,2Hj3NS4. 

A  very  similar  compound  containing  selenium  exists. 

Alanine. — This  substance  is  likewise  obtained  from  aldehyde.  It  Has 
been  only  recently  discovered  by  Strecker,  who  obtained  it  in  a  reaction, 
which  promises  many  interesting  results.  If  an  aqueous  solution  of  the  am- 
monia-compound of  aldehyde  be  treated  with  hydrocyanic  and  hydrochloric 
acid,  chloride  of  ammonium  is  formed,  together  with  hydrochlorate  of  ala- 
nine. On  adding  to  this  solution  a  mixture  of  alcohol  and  ether,  the  greater 
portion  of  the  chloride  of  ammonium  is  precipitated ;  the  filtrate  is  then 
treated  with  protoxide  of  lead  to  remove  a  small  quantity  of  ammonium  and 
hydrochloric  acid,  and  separated  from  the  lead  by  sulphuretted  hydrogen 
The  liquid  thus  obtained  deposits  feathery  crystals  of  alanine.  The  compo- 
sition of  alanine  is  C6H,N04,  and  its  formation  represented  by  the  equation: — 

C4H4OJJ     +     HCgN     -f     2HO=C6H7N04 

Aldehyde.     Hydrocyanic  Alanine. 

acid. 


468     APPENDIX  TO  THE  ORGANIC  BASES. 

Alanine  crystallizes  in  rhombic  prisms  of  the  lustre  of  mother-of-pearl.  They 
are  pretty  soluble  in  cold,  but  more  so  in  boiling  water ;  the  solution  has  a 
sweetish  taste,  but  no  effect  upon  vegetable  colours.  Alanine  is  a  weak  base; 
as  yet  only  a  crystalline  nitrate  has  been  obtained,  but  several  combinations 
with  metallic  oxides  have  been  produced.  This  substance  has  the  same  com- 
position as  lactamide  (see  page  351),  urethane  (see  page  358),  and  sarcosine, 
which  will  be  described  in  the  section  on  the  components  of  the  animal  body. 
But  it  is  only  isomeric  with  these  substances,  from  which  it  differs  th  its 
physical  and  chemical  properties.  The  most  interesting  feature  in  the  his- 
tory of  alanine  is  its  behaviour  witli  nitrous  acid.  Under  the  influence  of 
this  reagent  it  is  converted  into  lactic  acid,  identical  in  every  respect  with 
that  obtained  in  the  fermentation  of  sugar  (see  page  349).  This  reaction  is 
represented  by  the  following  equation  : — 

C6H7NO4 -{- NO3 = CgHgOg,  HO -f  2N4- HO 
Alanine.  Lactic  acid. 


APPENDIX   TO   THE    OROANIO    BASES. 


All  the  numerous  members  of  this  extensive  group,  whicli  have  been  con- 
sidered in  the  preceding  section,  invariably  contain  nitrogen.  Recent  re- 
searches, however,  have  shown  that  two  series  ff  analogous  substances  exist 
which  contain  phosphorus  and  antimony,  in  the  place  of  nitrogen.  These 
remarkable  compounds,  which  are  not  yet  sufficiently  known,  will  be  briefly 
noticed  in  the  subsequent  paragraphs. 

Phosphorus-bases. 

If  a  current  of  chloride  of  methyl  (see  page  382)  be  passed  over  a  layer 
of  phosphide  of  calcium  (see  page  241),  heated  to  about  356°  (180"C),  a 
mixture  of  several  phosphoretted  bodies  is  produced,  which  are  partly  liquid 
and  partly  solid.  M.  Paul  Th^nard,  who  has  investigated  this  subject,  has 
separated  from  this  mixture  three  compounds,  containing  carbon,  hydrogen, 
and  phosphorus,  which  he  believes  to  correspond  to  the  three  hydrides  of 
phosphorus  (see  page  166). 

Phosphoretted  Phosphoretted 

hydrogens.  methyl-bodies. 

TjH  PaCaHa^PjMe 

PH.  P2C2H3=PiMe2 

PH3 PSCgHg^PMea. 

As  far  as  can  be  seen  from  the  results  obtained  by  M.  Th^nard,  which 
have  not  yet  been  published  in  detail,  the  two  last  substances  are  powerful 
bases  analogous  to  the  bases  of  the  nitrogen-series.  These  substances  are 
very  readily  decomposed,  one  of  them  is  even  spontaneously  inflammable, 
so  that  their  preparation  and  study  has  been  attended  with  great  difficulty 
and  even  danger,  circumstances  which  sufficiently  account  for  the  insuffi- 
ciency of  the  description.  It  is  evident  that  the  last  body  is  the  phospho- 
retted analogue  of  trimethylamine,  triethylamine,  and  triamylamine,  and 
the  question  arises  whether  the  second  may  not  be  viewed  as  the  phospho- 
retted bimethylamine,  and  whether  farther  researches  will  not  establish  the 
existence  of  the  whole  series  of  the  phosphoretted  bases  corresponding  to 
the  compound  ammonias'  previously  described. 


APPENDIX    TO    THE    ORGANIC    BASES.  469 

Antimony -bases. 

Among  tLe  derivatives  of  alcohol,  a  compound  of  antimony  with  3  eq.  ot 
ethyl  has  been  briefly  noticed  see  page  (438)  under  the  name  of  stibethyl. 
The  composition  of  this  remarkable  compound  approximates  it  to  triethyla- 
mine. 

TriethyUmine  NAe, { """sSy?"  }  ^^^^ 

A  closer  examination  has  shown  that  this  substance  differs  in  many  points 
from  triethylamine,  but  that  in  one  very  essential  character,  the  two  sub- 
Btances  agree  in  the  most  perfect  manner. 

The  properties  of  stibethyl  are  the  following;  it  is  a  transparent,  very 
mobile  liquid,  of  a  penetrating  odour  of  onions.  It  boils  at  317°  (168°-3C). 
In  contact  with  atmospheric  air,  it  emits  a  dense  white  fume  and  frequently 
even  takes  fire,  burning  with  a  white  brilliant  flame.  It  combines  directly 
with  2  eq.  of  oxygen,  sulphur,  chlorine,  and  iodine. 

Binoxide  of  stibethyl,  SbAe302,  forms  a  viscid  transparent  mass  soluble  in 
water  and  alcohol.  It  is  extremely  bitter  and  not  poisonous.  This  sub- 
stance cannot  be  volatilized  without  decomposition.  Binoxide  of  stibethyl 
combines  with  acids,  giving  rise  to  the  formation  of  crystallizable  salts  con- 
taining 2  eq.  of  acid. 

Bisulphide  of  stibethyl,  SbAe3S2.  —  Beautiful  crystals  of  silvery  lustre,  so- 
luble in  water  and  alcohol.  Their  taste  is  bitter,  and  their  odour  similar  to 
that  of  mercaptan.  The  solution  of  this  compound  exhibits  the  deportment 
of.  an  alkaline  sulphide ;  it  precipitates  the  solution  of  the  metals  as  sul- 
phides, a  soluble  salt  of  stibethyl  being  formed  at  the  same  time.  This  de- 
portment, indeed,  affords  the  simplest  means  of  preparing  the  salts  of  stibe- 
thyl. 

Bichloride  of  stibethyl^  SbAcgClg.  —  Colourless  liquid  of  the  odour  of  oil  of 
turpentine. 

Biniodide  of  stibethyl,  SbAoglg.  —  Colourless  needles  of  intensely  bitter 
taste. 

The  analogy  of  stibethyl  with  triethylamine  is  best  exhibited  in  its  deport- 
ment with  iodide  of  ethyl.  The  two  substances  combine  to  a  new  iodide, 
containing  SbAe^I,  from  which  a  powerful  alkaline  base  may  be  separated 
by  the  action  of  protoxide  of  silver.  This  substance,  which  must  evidently 
be  analogous  to  oxide  of  tetrethyl-ammonium, 

NAe40,H0  SbAe^CHO, 

has  not  yet  been  minutely  examined. 

A  series  of  analogous  substances  exist  in  the  methyl-series.  They  have 
been  examined  by  M.  Landolt,  who  has  described  several  of  its  compounds, 
separated  the  methyl-antimony-base  corresponding  to  oxide  of  tetrethyl- 
ammonium. 

The  iodide,  SbMe4T,  produced  by  the  action  of  iodide  of  methyl  upon 
stibmethyl,  crystallizes  in  white  six-sided  tables,  which  are  easily  soluble  in 
water  and  alcohol,  and  slightly  soluble  in  ether.  It  has  a  very  bitter  taste, 
and  is  decomposed  by  the  action  of  heat.  When  treated  with  protoxide  of 
silver,  it  yields  a  powerfully  alkaline  solution  exhibiting  al!  the  properties 
of  potassa,  from  which,  on  evaporation,  a  white  crystalline  mabs,  the  hydrate 
of  the  base,  SbMe40,H0,  crystallizes.  This  compound  forms  an  acid  salt 
with  sulphuric  acid,  which  crystallizes  in  tables.  It  contains  SbMe.OjSO, 
-fH0,S03. 
40 


470  ORGANIC    COLOURING     PRINCIPLES 


SECTION    VI. 

ORGANIC   COLOURING   PRINCIPLES. 


The  organic  colouring  principles  are  substances  of  very  considerable  prac- 
tical importance  in  relation  to  the  arts;  several  of  them,  too,  have  been 
made  the  subjects  of  extensive  and  successful  chemical  investigation.  With 
the  exception  of  one  red  dye,  cochineal,  they  are  all  of  vegetable  origin. 

The  art  of  dyeing  is  founded  upon  an  affinity  or  attraction  existing 
between  the  colouring  matter  of  the  dye  and  the  fibre  of  the  fabric.  In 
■woollen  and  silk  this  affinity  is  usually  very  considerable,  and  to  such  tissues 
a  permanent  stain  is  very  easily  communicated,  but  with  cotton  and  flax  it 
is  much  weaker.  Recourse  is  then  had  to  a  third  substance,  which  does 
possess  in  a  high  degree  such  affinity,  and  with  this  the  cloth  is  impregnated. 
Alumina,  sesquioxide  of  iron,  and  oxide  of  tin  are  bodies  of  this  class. 

When  an  infusion  of  some  dye-wood,  as  logwood,  for  example,  is  mixed 
with  alum  and  a  little  alkali,  a  precipitate  falls,  consisting  of  alumina  in 
combination  with  colouring  matter,  called  a  lake;  it  is  by  the  formation  of 
this  insoluble  substance  within  the  fibre  that  a  permanent  dyeing  of  the 
cloth  is  eflFected.  Such  applications  are  termed  mordants.  Sesquioxide  of 
iron  usually  gives  rise  to  dull,  heavy  colours ;  alumina  and  oxide  of  tin, 
especially  the  latter,  to  brilliant  ones.  It  is  easy  to  see,  that,  by  applying 
the  mordant  partially  to  the  cloth,  by  a  wood-block  or  otherwise,  a  pattern 
may  be  produced,  as  the  colour  will  be  removed  bv  washing  from  the  other 
portions. 


Indigo  is  the  most  important  member  of  the  group  of  blue  colouring 
matters.  It  is  the  product  of  several  species  of  the  genus  indigofera^  which 
grow  principally  in  warm  climates.  When  the  leaves  of  these  plants  are 
placed  in  a  vessel  of  water  and  allowed  to  ferment,  a  yellow  substance  is 
dissolved  out,  which  by  contact  of  air  becomes  deep  blue  and  insoluble,  and 
finally  precipitates.  This,  washed  and  carefully  dried,  constitutes  the  indigo 
of  commerce.  It  is  not  contained  ready-formed  in  the  plant,  but*is  pro- 
duced by  the  oxidation  of  some  substance  there  present.  Neither  is  the 
fermentation  essential,  as  a  mere  infusion  of  the  plant  in  hot  water  deposits 
*ndigo  by  standing  in  the  air. 

Indigo  comes  into  the  market  in  the  form  of  cubic  cakes,  which,  rubbed 
ith  a  hard  body,  exhibit  a  copper-red  appearance ;  its  powder  has  an  in- 
tensely deep  blue  tint.  The  best  is  so  light  as  to  swim  upon  water.  In 
addition  to  the  blue  colouring  matter,  or  true  indigo,  it  contains  at  least  half 
its  weight  of  various  impurities,  among  which  may  be  noticed  a  red  resinous 
matter,  the  indigo-red  of  Berzelius ;  these  may  be  extracted  by  boiling  the 
powdered  indigo  in  dilute  acid,  alkali,  and  afterwards  in  alcohol. 

Pure  indigo  is  quite  insoluble  in  water,  alcohol,  oils,  dilute  acids,  and 
alkalis ;  it  dissolves  in  about  15  parts  of  concentrated  sulphuric  acid,  forming 


INDIGO.  471 

a  deep  blue  pasty  mass,  entirely  soluble  in  water,  and  often  used  in  dyeing ; 
this  is  sulphindylic  or  sulpMndigotic  acid,  a  compound  analogous  to  sulphovinio 
acid,  capable  of  forming  with  alkaline  bases  blue  salts,  which,  although  easily 
soluble  in  pure  water,  are  insoluble  in  saline  solutions.  If  an  insufficient 
quantity  of  sulphuric  acid  has  been  employed,  or  digestion  not  long  enough 
continued,  a  purple  powder  is  left  on  diluting  the  acid  mass,  soluble  in  a 
large  quantity  of  pure  water.  The  Nordhausen  acid  answers  far  better  for 
dissolving  indigo  than  ordinary  oil  of  vitriol.  Indigo  may,  by  cautious  man- 
agement, be  volatilized ;  it  fonns  a  fine  purple  vapour,  which  condenses  in 
brilliant  copper-coloured  needles.  The  best  method  of  subliming  this  sub- 
stance is,  according  to  Mr.  Taylor,  to  mix  it  with  plaster  of  Paris,  make  the 
whole  into  a  paste  with  water,  and  spread  it  upon  an  iron  plate.  1  part  in- 
digo, and  2  parts  plaster,  answer  very  well.  This,  when  quite  dry,  is  heated 
by  a  spirit-lamp ;  the  volatilization  of  the  indigo  is  aided  by  the  vapour  of 
water  disengaged  from  the  gypsum,  and  the  surface  of  the  mass  becomes 
covered  with  beautiful  crystals  of  pure  indigo,  which  may  be  easily  removed 
by  a  thin  spatula.  At  a  higher  temperature,  charring  and  decomposition 
take  place. 

In  contact  with  de-oxidizing  agents,  and  with  an  alkali,  indigo  suffers  a 
very  curious  change ;  it  becomes  soIuIdIc  and  nearly  colourless,  perhaps  re- 
turning to  the  same  state  in  which  it  existed  in  the  plant.  It  is  on  this  prin- 
ciple that  the  dyer  prepares  his  indigo-vat : — 5  parts  of  powdered  indigo,  10 
parts  of  green  vitriol,  15  parts  of  hydrate  of  lime,  and  60  parts  of  water,  are 
agitated  together  in  a  close  vessel,  and  then  left  to  stand.  The  hydrated 
protoxide  of  iron,  in  conjunction  with  the  excess  of  lime,  reduces  the  indigo 
to  the  soluble  state ;  a  yellowish  liquid  is  produced,  from  which  acids  pre- 
cipitate the  white  or  de-oxidized  indigo  as  a  flocculent  insoluble  substance, 
which  absorbs  oxygen  with  the  greatest  avidity,  and  becomes  blue.  Cloth 
steeped  in  the  alkaline  liquid,  and  then  exposed  to  the  air,  acquires  a  deep 
and  most  permanent  blue  tint  by  the  deposition  of  solid  insoluble  indigo  in 
the  substance  of  the  fibre.  Instead  of  the  iron-salt  and  lime,  a  mixture  of 
dilute  caustic  soda  and  grape-sugar  dissolved  in  alcohol  may  be  used  ;  the 
sugar  becomes  pxidized  to  formic  acid,  and  the  indigo  reduced.  On  allowing 
a  solution  of  this  description  to  remain  in  contact  with  the  air,  it  absorbs 
oxygen  and  deposits  the  indigo  in  the  crystalline  condition. 

The  following  formulae  represent  the  composition  of  the  bodies  described:^ 

Blue  insoluble  indigo  CjeHgN  Oj 

White,  or  reduced  indigo* CigHgN  Og 

Sulphindylic  acid CigH^N  0,2S03,  HO. 

Products  of  the  Decomposition  of  Indigo. 

The  products  of  the  destructive  modification  of  indigo  by  powerful  chemical 
agents  of  an  oxidizing  nature  are  both  numerous  and  interesting,  inasmuch 
as  they  connect  this  substance  in  a  very  curious  manner  with  several  other 
groups  of  organic  bodies,  especially  with  those  of  the  salicyl-  and  phenyl- 
series.  Many  of  them  are  exceedingly  beautiful,  and  possess  very  remarkable 
properties. 

IsATiN. — One  part  of  indigo  reduced  to  fine  powder,  and  rubbed  to  a  paste 
with  water,  is  gently  heated  with  a  mixture  of  one  part  of  sulphuric  acid 
and  one  part  of  bichromate  of  potassa  dissolved  in  20  or  30  parts  of  water 

*  Properly  hydrogenized  indigo,  if  the  above  be  the  correct  view :  white  indigo  may,  how 
ever,  be  viewed  as  a  hydrate,  and  blue  indigo  as  an  oxide,  of  one  and  the  fame  substance. 

White  indigo CieHSN  0+HO 

Blue  indigo  ....- CieH^NO+O 


472  INDIGO. 

The  indigo  dissolves  "witli  very  slight  disengagement  of  carbonic  acid  towards 
the  end,  forming  a  yellow-brown  solution,  which  on  standing  deposits  impure 
isatin  in  crystals.  These  are  collected,  slightly  washed  and  re-dissolved  in 
boiling  water;  the  filtered  solution  deposits  on  cooling  the  isatin  in  a  state 
of  purity.  Or,  powdered  indigo  may  be  mixed  with  water  to  a  thin  paste, 
heated  to  the  boiling-point  in  a  large  capsule,  and  nitric  acid  added  by  small 
portions  until  the  colour  disappears ;  the  whole  is  then  largely  diluted  with 
boiling  water,  and  filtered.  The  impure  isatin  which  separates  on  cooling  is 
washed  with  water  containing  a  little  ammonia,  and  re-crystallized.  Both 
these  processes  require  careful  management,  or  the  oxidizing  action  proceeds 
too  far,  and  the  product  is  destroyed. 

Isatin  forms  deep  yellowish-red  prismatic  crystals  of  great  beauty  and 
lustre ;  it  is  sparingly  soluble  in  cold  water,  freely  in  boiling  water,  and  also 
in  alcohol.  The  solution  colours  the  skin  yellow,  and  causes  it  to  emit  a 
very  disagreeable  odour.  It  cannot  be  sublimed.  Isatin  contains  the  elements 
of  indigo  jtJ^ws  2  eq.  of  oxygen,  or  CigHgNO^. 

A  solution  of  potassa  dissolyes  isatin  with  purple  colour ;  from  this  solu- 
tion acids  precipitate  the  isatin  unchanged.  When  boiled,  however,  the 
colour  is  destroyed,  and  the  liquid  furnishes  on  evaporation  crystals  of  the 
potassa-salt  of  a  new  acid,  the  isatinic,  containing  CigHgNOgjHO.  In  the 
free  state  this  is  a  white  and  imperfectly  crystalline  powder,  soluble  in 
water,  and  easily  decomposed  into  isatin  and  water. 

By  chlorine,  isatin  is  converted  into  the  substitution-product  chlorisatin, 
Cj6(H4Cl)N04,  a  body  closely  resembling  isatin  itself  in  properties.  If  an 
alcoholic  solution  and  excess  of  chlorine  be  employed,  other  products  make 
their  appearance,  as  chloranile,  C12CI4O4,  trichlorophenol,  Ci2(H3Cl3)02,  and  a 
resinous  substance.  The  former  of  these  substances,  the  position  of  which 
in  the  kinone-series  has  been  already  noticed  (page  449),  yields  other  pro- 
ducts with  potassa  and  ammonia.  Bromisatin  is  easily  formed.  The  changes 
which  isatin,  and  its  chlorinetted  and  brominetted  congeners,  undergo  when 
submitted  to  the  action  of  fusing  hydrate  of  potassa  has  been  already  con- 
sidered in  the  section  on  the  vegeto-alkalis  (see  page  459). 

Exposed  to  the  action  of  sulphuretted  hydrogen  and  sulphide  of  ammo- 
nium, isatin  furnishes  several  new  compounds,  as  isatht/de,  sulfesathyde,  sulfa- 
sathyde. 

A  hot  solution  of  isatin,  when  treated  with  sulphide  of  ammonium,  gives 
rise  to  a  deposit  of  sulphur,  a  white  crystallized  substance  being  produced 
at  the  same  time ;  it  has  received  the  name  of  isathyde,  and  contains  CjgHg 
NO4.  It  is  obvious  that  it  bears  to  isatin  the  same  relation  as  white  to  blue 
indigo.  If  the  sulphide  of  ammonium  be  replaced  by  sulphuretted  hydro- 
gen, hisulphisathyde,  Ci6HgN02S2,  is  produced,  which  is  unlike  the  former;  2 
eq.  of  oxygen,  being  replaced  by  2  eq.  of  sulphur.  An  alcoholic  solution  of 
potassa  converts  this  into  sulphisathyde,  CigHgNOgS,  in  which  only  half  of  the 
oxygen  in  isatin  is  replaced  by  sulphur.  Under  the  influence  of  cold  aque- 
ous solution  of  potassa,  hisulphisathyde  yields  indin,  CjgHgNOg,  which  is  iso- 
meric with  white  indigo.  When  treated  with  boiling  potassa,  indin  fixes  the 
elements  of  2  eq.  of  water,  and  becomes  indinic  acid,  CigH^NOgjHO,  the  po- 
tassa-salt of  which  forms  fine  black  needles. 

Ammoniacal  gas  and  solution  of  ammonia  yield  with  isatin  a  series  of  in- 
teresting substances  containing  the  nitrogen  of  the  ammonia  in  addition  to 
that  of  the  isatin. 

Action  of  chlorine  on  indigo.  —  In  the  dry  state  chlorine  has  no  action 
whatever  on  indigo,  even  at  the  temperature  of  212°  (100°C).  In  contact 
■with  water,  the  blue  colour  is  instantly  destroyed,  and  cannot  again  be  re- 
stored. The  same  thing  happens  with  the  blue  solution  of  sulphindylic  acid. 
When  chlorine  is  passed  into  a  mixture  of  powdered  indigo  and  water  until 


I  N  D  T  G  O  .  473 

the  colour  disappears,  &ni\  the  product  is  then  distilled  in  a  retort,  water 
containing  hydrochloric  acid  and  a  mixture  of  two  volatile  bodies,  trichlor- 
aniline,  Ci2(H4Cl3)N,  and  trichlorophenol,  C,2(H3C]3)02,  pass  over  into  the 
receiver,  while  the  residue  in  the  retort  is  found  to  contain  chlorisatin,  al- 
ready mentioned,  and  bichlorisatin,  Ci6(H3Cl2)N04,  much  resembling  that  sub- 
stance, but  more  freely  soluble  in  alcohol.  Both  these  bodies  yield  acids  in 
contact  with  boiling  solution  of  potassa,  by  assimilating  the  elements  of  water. 

The  action  of  bromine  on  indigo  is  very  similar. 

Anilic  and  picric  acids. — Anilic  or  indigotic  acid  is  prepared  by  adding 
powdered  indigo  to  a  boiling  mixture  of  1  part  of  nitric  acid  and  10  parts 
of  water,  until  the  disengagement  of  gas  ceases,  filtering  the  hot  dark- 
coloured  liquid,  and  allowing  it  to  stand.  The  impure  anilic  acid  so  ob- 
tained is  converted  into  the  lead-salt,  which  is  purified  by  crystallization  and 
the  use  x)f  animal  charcoal,  and  then  decomposed  by  sulphuric  acid.  Anilic 
acid  forms  fine  white  or  yellowish  needles,  which  have  a  feeble  acid  taste 
and  very  sparing  degree  of  solubility  in  cold  water.  In  hot  water  and  in 
alcohol  it  dissolves  easily.  It  melts  when  heated,  and  on  cooling  assumes 
a  crystalline  structure.  By  careful  management  it  may  be  sublimed  un- 
changed. Anilic  acid  contains  Ci4H4N09,HO=C,4(H4N04)05,HO.  It  has 
been  mentioned  that  the  same  acid  is  readily  prepared  from  salicylic  acid 
(see  page  406).     Hence  it  is  more  appropriately  called  nitro-salicylic  acid. 

Picric,  carbazotic,  or  nitrophenisic  acid,  is  one  of  the  ultimate  products 
of  the  action  of  nitric  acid  upon  indigo  and  numerous  other  substances,  as 
silk,  wool,  several  resins,  especially  that  of  Xanthorhcea  hastilis  (yellow  gum 
of  Botany  Bay),  salicin  and  some  of  its  derivatives,  cumarin,  and  certain 
bodies  belonging  to  the  phenyl-series.  It  may  be  prepared  from  indigo  by 
adding  that  substance  in  coarse  powder  and  by  small  portions  to  ten  or 
twelve  times  its  weight  of  boiling  nitric  acid  of  sp.  gr.  1-43.  When  the  last 
of  the  indigo  has  been  added,  and  the  action,  at  first  extremely  violent,  has 
become  moderated,  an  additional  quantity  of  nitric  acid  may  be  poured  upon 
the  mixture,  and  the  boiling  kept  up  until  the  evolution  of  red  fumes  nearly 
ceases.  When  cold,  the  impure  picric  acid  obtained  may  be  removed,  con- 
verted into  potassa-salt,  several  times  re-crystallized,  and,  lastly,  decom- 
posed by  nitric  acid.  In  the  pure  state  it  forms  beautiful  pale  yellow  scaly 
crystals,  but  slightly  soluble  in  cold  water,  and  of  insuppor^ably  bitter  taste. 
Picric  acid  is  used  in  dyeing ;  it  forms  a  series  of  crystallia^le  salts  of  yel- 
low or  orange  colour :  that  of  potassa  forms  brilliant  needl»»nd  is  so  little 
soluble  in  cold  water,  that  a  solution  of  picric  acid  is  occapHElly  used  as  a 
precipitant  for  that  base.  The  alkaline  salts  of  this  aciie^lode  by  heat 
with  extraordinary  violence.  The  crystals  of  picric  acic^contain  CioHoN, 
Oi3,HO. 

If  a  solution  of  picric  acid  be  distilled  with  hydrochlorite  of  lime,  or  a 
mixture  of  chlorate  of  potassa  and  hydrochloric  acid,  an  oily  liquid  of  a 
penetrating  odour  is  obtained,  having  a  sp.  gr.^of  1-665,  and  boiling  between 
237°  and  239°  (114°  and  115°C).  '  The  substance,  chloropicrin,  was  disco- 
vered by  Stenhouse,  who  gives  the  formula  C4CI7N2O10;  MM.  Gerhardt  and 
Cahours  assign  to  it  the  formula  C2CI3NO4.  According  to  the  latter  formula, 
which  is  more  probable,  chloropicrin  would  be  chloroform,  in  which  the  hy- 
drogen is  replaced  by  the  elements  of  hyponitric  acid : 

Chloroform  C2(HCl3) ;  Chloropicrin  C2(N04Cl3). 

Products  of  the  action  of  hydrate  of  potassa  upon  indigo. — One  of 
the  most  remarkable  of  these,  aniline,  has  been  already  described  (see  page 
459).  When  powdered  indigo  is  boiled  with  a  very  concentrated  solution  of 
caustic  potassa,  it  is  gradually  dissolved  with  the  exception  of  some  brown- 
ish flocculent  matter,  and  the  liquid  on  cooling  deposits  yellDW  crystals  of 
40* 


474  LICHENS. 

the  potassa-salt  of  a  new  acid,  the  chrysanilic,  which  can  be  procured  in  a 
purer  state,  by  dissolving  the  crystals  in  water,  filtering  from  reproduced 
indigo,  and  adding  a  slight  excess  of  mineral  acid,  Chrysanilic  acid  can  be 
obtained  in  indistinct  crystals  from  weak  alcohol ;  it  is  supposed  to  contain 
C28^^ioN2^5'HO,  but  it  is  very  probable  that  it  is  a  mixture  of  several  sub- 
stances, especially  isatinic  acid. 

When  this  substance  is  boiled  with  mineral  acids,  it  is  decomposed  into 
another  new  acid,  the  anthranilic,  which  remains  in  solution,  and  a  blue  in- 
soluble matter  resembling  indigo ;  a  similar  effect  is  slowly  produced  by  the 
action  of  the  air  upon  an  alcoholic  solution  of  chrysanilic  acid.  Anthranilic 
acid  is  colourless,  sparingly  soluble  in  cold  water,  easily  soluble  in  alcohol. 
It  melts  when  heated,  sublimes  under  favourable  circumstances,  but  decom- 
poses entirely  when  heated  in  a  narrow  tube  into  carbonic  acid  and  aniline. 
It  contains  Ci4HgN03,HO.  By  treatment  vnth  nitrous  acid,  anthranilic  acid 
is  converted  into  salicylic  acid  C,4HeN03,HO-fN03=Cj4H505,HO-f  H0-|-2N. 

According  to  M.  Cahours,  pure  indigo  can  also  be  converted  into  salicylic 
acid  by  fusion  with  hydrate  of  potassa  ;  a  particular  temperature  is  required, 
somewhat  above  570°  (298°C),  and  the  operation  is  by  no  means  always 
successful. 


Litmus  is  used  by  the  dyer  as  a  red  colouring  matter  ;  the  chemist  employs 
it  in  the  blue  state  as  a  test  for  the  presence  of  acid,  by  which  it  is  instantly 
reddened. 

In  preparing  test-papers  for  chemical  use  with  infusion  of  litmus,  good 
writing  or  drawing-paper,  free  from  alum  and  other  -acid  salts,  should  be 
chosen.  Those  sheets  which  after  drying  exhibit  red  spots  or  patches,  may 
be  reddened  completely  by  a  little  dilute  acetic  acid,  and  used,  with  much 
greater  advantage  than  turmeric-paper,  to  discover  the  presence  of  free 
alkali,  which  restores  the  blue  colour. 

Many  lichens,  when  exposed  in  a  moistened  state  to  the  action  of  ammonia, 
yield  purple  or  blue  colouring  principles,  which,  like  indigo,  do  not  pre- 
exist in  the  plant  itself.  Thus,  the  Roccella  tinctoria,  the  Variolai-ia  orcina, 
the  Lecanora  tartarea,  &c.,  when  ground  to  paste  with  water,  mixed  with 
putrid  urine  or  solution  of  carbonate  of  ammonia,  and  left  for  some  time 
freely  exposed  to  the  air,  furnish  the  archil,  litmus,  and  cudbear  of  commerce, 
very  similar  substances,  diflfering  chiefly  in  the  details  of  the  preparation. 
From  these  tb<M5olouring  matter  is  easily  extracted  by  water  or  very  dilute 
solution  of  ammonia. 

The  lichens  Mlve  been  extensively  examined  by  Schunk,  Stenhouse,  and 
several  other  chemists.  The  whole  subject  has  been  lately  revised  by  Dr. 
Strecker,  whose  formulae  have  been  adopted  in  the  following  succinct  ac- 
count:— 

Erythric  acid. — The  lichen  Roccella  tinctoria,  from  which  the  finest  kind 
of  archil  is  prepared,  is  boiled  with  milk  of  lime,  the  filtered  solution  is  pre- 
cipitated by  hydrochloric  acid,  and  the  precipitate  dried  and  dissolved  in 
warm,  not  boiling,  alcohol,  from  which  on  cooling  crystals  of  erythric  acid  are 
deposited.  This  is  a  very  feeble  acid,  colourless,  inodorous,  difficultly  solu- 
ble in  cold  and  even  in  boiling  water,  readily  soluble  in  ether.  Its  solution, 
when  mixed  with  chloride  of  lime,  assumes  a  blood-red  colour.  Boiled  with 
water  for  some  time,  erythric  acid  absorbs  2  eq.  and  yields  picro-erythrin,  a 
crystallizable,  bitter  principle,  and  a  new  acid  presently  to  be  described, 
which  is  termed  by  some  chemists  lecanoric,  by  others  orsellinic  acid.  If  the 
ebullition  be  continued,  the  orsellinic  acid  undergoes  a  farther  change,  being 
converted  into  a  crystalline  substance,  orcin,  of  which  mention  will  shortly 
be  made. 


LICHENS.  475 

The  composition  of  these  various  substances  is  expressed  by  the  following 
formuloB : — 

Erythric  acid C2oHjiOjq 

Orselliuic  acid CjgH  gO  g 

Picro-erythrin , C24HjeOj4 

Orcin C,4H  gO  4 

And  the  successive  changes  which  occur  by  ebullition  are  represented  by  the 
following  equation :  — 

2C2oHhO,o+2HO     =     CjeHgOg     +     C^T{,,0,, 
Erythric  acid.  Orsellinic  acid.    Picro-erythrin. 

CieHgOg    =     C,4H804     +     2C08 
Orsellinic  acid,        Orcin. 

Alphaorsellic  acid  is  obtained  from  the  South  American  variety  ol 
Roccella  tinctoria.  The  preparation  and  the  properties  of  this  substance  are 
perfectly  analogous  to  those  of  erythric  acid.  Alphaorsellic  acid  contains 
€3211,40,4  ;  by  boiling  with  baryta- water  it  likewise  furnishes  orsellinic  acid. 

Cyff,4_0^4-f2HO    =    2C,eHgOg 

Alphaorsellic  Orsellinic  acid, 

acid. 

If  the  ebullition  be  continued  too  long,  a  great  portion  of  the  orsellinic 
acid  is  converted  into  orcin. 

Orsellinic  acid,  formerly  frequently  called  lecanoric  acid,  whether  pre- 
pared from  erythric  or  alphaorsellic  acid,  forms  crystals  which  are  far  more 
soluble  in  water  than  either  of  the  acids  from  which  it  has  been  prepared. 
Its  taste  is  somewhat  bitter.  Boiled  with  water,  it  yields,  as  has  been 
stated,  orcin ;  under  the  influence  of  air  and  ammonia,  it  assumes  a  beauti- 
ful  purple  colour. 

If  the  lichens,  instead  of  being  treated  with  milk  of  lime,  be  exhausted 
with  boiling  alcohol,  the  erythric  and  alphaorsellic  acids  are  likewise  decom- 
posed; but  instead  of  orsellinic  acid,  the  ether  of  this  substance,  C4H5O, 
C16H7O7,  is  formed.  This  ether  was  formerly  described  under  the  name 
pseudo-erythrin  until  Mr.  Schunk  pointed  out  the  true  nature  of  the  sub- 
stance. Orsellinate  of  ethyl  may  be  likewise  produced  by  boiling  pure 
orsellinic  acid  with  alcohol.  It  crystallizes  in  colourless  lustrous  plates, 
which  are  readily  soluble  in  boiling  water,  alcohol,  and  ether. 

Betaoksellic  acid  is  found  in  Roccella  tinctoria  grown  at  the  Cape  ;  it  ia 
obtained  like  erythric  and  alphaorsellic  acid,  which  it  resembles  in  proper- 
ties. Betaorsellic  acid  contains  Cj^HjgOjg ;  by  boiling  with  water,  it  yields 
likewise  orsellinic  acid,  together  with  hair-like  crystals  of  a  silvery  lustre, 
of  a  substance  called  roccellinin,  which  has  the  composition  CigllgO,. 

^34^i6"i5         =         C,eHgOg         -f-         CjgHgOY 

Betaorsellic  acid.        Orsellinic  acid.  Roccellinin. 

The  decomposition  of  betaorsellic  acid  is  obviously  analogous  to  that  of 
erythric  acid,  the  roccellinin  representing  the  picro-erythrin. 

Evernic  acid  is  extracted  by  milk  of  lime  from  Evernia  prunastri,  which 
was  formerly  believed  to  contain  orsellinic  acid.  Evernic  acid  is  very  diffi- 
cultly soluble  even  in  boiling  water ;  it  assumes  a  yellow  colour  with  chlo- 


476  LICHENS. 

ride  of  lime.  When  boiled  with  the  alkalis,  it  yields  another  crystalline 
acid,  everninic  acid,  differing  from  the  preceding  by  its  free  solubility  in 
boiling  water.  The  composition  of  evernic  acid  is  represented  by  the  for- 
mula Cg^lIjgOj^,  that  of  everninic  acid  by  CigHigOg.  Evernic  acid,  when 
boiled  for  a  considerable  time  with  baryta,  yields  orcin ;  everninic  acid  does 
not  give  a  trace  of  this  substance  ;  it  is  therefore  probable  that  evernic  acid, 
under  the  influence  of  alkalis,  yields  in  addition  to  everninic  acid  likewise 
orsellinic  acid,  from  which  the  orcin  is  derived,  and  that  this  decomposition 
is  represented  by  the  equation : — 

C3^,eOH+2HO       =       C^HgOg^      +       CigHioOg 

Evernic  acid.  Orsellinic  aJid.     Everninic  acid. 

Pabellic  acid. — Lecanora  parella  contains  an  acid  probably  analogous  to 
erythric,  alphaorsellic,  betaorsellic,  and  evernic  acids,  the  composition  of 
which  is,  however,  still  unknown.  By  boiling  with  baryta  it  yields  orsellinic 
acid  &nd par ellic  acid,  CjgHgOg. 

Orcin  is  the  general  product  of  decompositions  of  the  acids  previously 
described  under  the  influence  of  heat  or  alkaline  earths. 

Orcin  is  best  prepared  by  boiling  lecanoric  or  orsellinic  acid,  pure  or  im- 
pure, with  baryta- water,  precipitating  the  excess  of  baryta  by  carbonic  acid, 
and  evaporating  the  filtered  liquid  to  a  small  bulk.  It  forms,  when  pure, 
large,  square  prisms,  which  have  a  slightly  yellowish  tint,  an  intensely 
sweet  taste,  and  a  high  degree  of  solubility  both  in  water  and  alcohol.  When 
heated,  orcin  loses  water  and  melts  to  a  syrupy  liquid  which  distils  un- 
changed.    The  crystals  of  orcin  contain  C]4H804,2HO. 

Orcein.  — When  ammonia  is  added  to  a  solution  of  orcin,  and  the  whole 
exposed  to  the  air,  the  liquid  assumes  a  dark  red  or  purple  tint,  by  absorp- 
tion of  oxygen  ;  a  slight  excess  of  acetic  acid  then  causes  the  precipitation 
of  a  deep  red  powder,  not  very  soluble  in  water,  but  freely  dissolving  in 
ammonia  and  fixed  alkalis,  with  a  purple  or  violet  colour.  This  is  an  azo- 
tized  substance,  formed  from  the  elements  of  the  ammonia  and  the  orcin, 
called  orcein  ;  it  probably  constitutes  the  chief  ingredient  of  the  red  dye- 
stuff  of  the  commercial  articles  before  mentioned.  The  composition  of 
orcein  is  less  certain  than  that  of  orcin;  it  probably  contains  C,4H7N0g, 
when  its  formation  from  orcin,  under  the  joint  influence  of  oxvgen  and 
ammonia,  would  be  represented  by  the  equation  : — 

C,4Hg04,2HO+60-fNH3    =     C,4H,N06-f6H0 

Orcin.  Orcein. 

Other  substances  are  occasionally  present  in  lichens;  thus,  the  Usnea 
barbata  and  several  other  lichens  contain  usnic  acid,  a  substance  crystallizing 
from  alcohol  in  fine  yellowish-white  needles  with  metallic  lustre,  having  the 
formula  C34HigOi4.  It  gives  no  orcin  by  distillation,  but  a  substance  similar 
to  it,  which  probably  contains  CggHjgOg,  and  has  been  designated  by  the 
name  of  betaorcin.  Its  formation,  which  is  attended  by  an  evolution  of  car- 
bonic acid,  is  represented  by  the  equation  ; — 

CssH  180,4       =       C34H,806-}-4C02 

Usnic  acid.  Betaorcin. 

The  Parmelia  parietina  furnishes  another  new  substance,  cTirysophanic  acid, 
crystallizing  in  fine  golden-yellow  needles  and  containing  CJ0H4O3.  It  is  a 
very  stable  substance,  and  may  be  sublimed  without  much  decomposition. 


RED    AND    YELLOW    D\   £S.  477 


BED   AND   YELLOW   DYES. 


Cochineal. — This  is  a  little  insect,  the  Coccus  cacti,  which  lives  on  several 
species  of  cactus,  which  are  found  in  warm  climates,  and  cultivated  for  the 
purpose,  as  in  Central  America.  The  dried  body  of  the  insect  yields  to  water 
and  alcohol  a  magnificent  red  colouring  matter,  precipitable  by  alumina  and 
oxide  of  tin  ;  carmine  is  a  preparation  of  this  kind.  In  cochineal  the  colour- 
ing matter  is  associated  with  several  inorganic  salts,  especially  phosphates 
and  nitrogenetted  substances.  Mr.  Warren  De  La  Rue,  who  has  published 
a  very  elaborate  investigation  of  cochineal,'  has  separated  the  pure  colouring 
matter,  which  he  calls  carminic  acid,  by  the  following  process.  The  aqueous 
decoction  of  the  insect  is  precipitated  by  the  acetate  of  lead,  and  the  impure 
carminate  of  lead  washed  and  decomposed  by  hydrosulphuric  acid  ;  the 
colouring  matter  thus  separated  is  submitted  again  to  the  same  treatment. 
A  solution  of  carminic  acid  is  thus  obtained,  which  is  evaporated  to  dryness, 
re-dissolved  in  absolute  alcohol,  and  digested  with  crude  carminate  of  lead, 
whereby  a  small  quantity  of  phosphoric  acid  is  separated,  and  lastly  mixed 
with  ether,  which  separates  a  trace  of  a  nitrogenetted  substance.  The 
residue  now  obtained  on  evaporation  is  pure  carminic  acid.  It  is  a  purple- 
brown  mass,  yielding  a  fine  red  powder,  soluble  in  water  and  alcohol  in  all 
proportions,  slightly  soluble  in  ether.  It  is  soluble  without  decomposition 
in  concentrated  sulphuric  acid,  but  readily  attacked  by  chlorine,  bromine, 
and  iodine,  which  change  its  colour  to  yellow.  It  resists  a  temperature  of 
276°-8  (136°C),  but  is  charred  when  heated  more  strongly.  Carminic  acid 
is  a  feeble  acid.  The  composition  of  the  substance,  dried  at  248°  (120°C), 
is  represented  by  CjgHi^Ojg,  which  formula  was  corroborated  by  the  analysis 
of  a  copper-compound,  CuOjCjgHj^Oig. 

By  the  action  of  nitric  acid  upon  carminic  acid,  together  with  oxalic  acid, 
a  splendid  nitrogenetted  acid,  crystallizing  in  yellow  rhombic  plates,  is  ob- 
tained. This  substance,  to  which  the  name  nitrococcusic  acid  was  given,  is 
bibasic ;  it  contains  Ci6H3N30,g,2HO.  It  is  soluble  in  cold,  and  more  so  in 
boiling  water,  readily  soluble  in  alcohol  and  ether.  Nitrococcusic  acid  is 
evidently  derived  from  a  non-nitrogenous  compound  in  which  part  of  the 
hydrogen  is  replaced  by  the  elements  of  hyponitric  acid.  Like  the  sub- 
stances of  this  class,  it  explodes  when  heated. 

In  the  mother-liquor,  from  which  the  carminic  acid  has  been  separated, 
Mr.  Warren  De  La  Rue  discovered  a  white,  crystalline,  nitrogenetted  sub- 
stance, for  which  he  established  the  formula  C,f,Hj,NOg,  This  substance  is 
identical  with  tyrosine,  which  will  be  mentioned  in  the  section  on  Animal 
Chemistry. 

Madder. — The  root  of  the  Rubia  tinctorum,  cultivated  in  southern  France, 
the  Levant,  &c.,  is  the  most  permanent  and  valuable  of  the  red  dye-stuffs. 
In  addition  to  several  yellow  colouring  matters,  which  are  of  little  impor- 
tance for  the  purposes  of  the  dyer,  madder  contains  two  red  pigments  which 
are  called  alizarin  and  purpurin.  These  substances  have  been  the  subject  of 
very  extensive  researches  by  Debus,  Higgins,  and  especially  by  Schunk.  The 
latest  papers  on  madder  have  been  published  by  Wolff  and  Strecker,  whose 
formulas  are  quoted  in  the  following  abstract. 

Alizarin. — The  aqueous  decoction  of  madder  is  precipitated  by  sulphuric 
acid,  and  the  precipitate  washed  and  boiled  with  sesquichloride  of  aluminum, 
which  dissolves  the  red  pigments;  an  insoluble  brownish  residue  remaining 
behind.  The  solution,  when  mixed  with  hydrochloric  acid,  yields  a  precipi- 
tate consisting  chiefly  of  alizarin,  however,  still  contaminated  with  purpurin. 
The  impure  alizarin  tlius  obtained  may  be  farther  purified  by  again  throwing 

*  Mem.  of  the  Chem.  Soc,  vol.  iii.  p.  454. 


478  RED    AND    YELLOW    DYES. 

down  the  alcdholic  solution  with  hydrate  of  alumina,  and  boiling  the  preci- 
pitate with  a  concentrated  solution  of  soda,  which  leaves  a  pure  compound 
of  alumina  and  alizarin  behind.  From  this  the  alizarin  is  separated  by 
hydrochloric  acid,  and  re-crystallized  from  alcohol.  Pure  alizarin  crystal- 
lizes in  splendid  red  prisms,  which  may  be  sublimed.  It  is  but  slightly  solu- 
ble in  water  and  in  alcohol,  but  dissolves  in  concentrated  sulphuric  acid  with 
a  deep  red  colour.  On  addition  of  water,  the  colouring  matter  is  re-precipi- 
tated unchanged.  It  is  also  soluble  in  alkaline  liquids,  to  which  it  imparts 
a  magnificent  purple  colour.  It  is  insoluble  in  cold  solution  of  alum.  Ali- 
zarin is  the  chief  colouring  matter  of  madder ;  it  contains  C2QHeO^-\-'iilO,  and 
is  a  feeble  acid  ;  but  a  few  definite  compounds  with  mineral  oxides  have  been 
prepared,  among  which  a  lime-compound,  C2oH60g,3CaO-|-3HO,  may  be 
quoted.  The  action  of  nitric  acid  upon  alizarin  gives  rise  to  the  formation 
of  oxalic  acid  and  phthalic  acid,  a  substance  which  will  again  be  men- 
tioned among  the  products  of  decomposition  of  naphthalin. 

C2oH606+2H04.80  =  2(C203.HO)-f  CieHeOs 

Alizarin.  Phthalic  acid. 

PuRPURiN.  —  Madder  is  allowed  to  ferment  and  then  boiled  with  a  strong 
solution  of  alum.  The  solution,  when  mixed  with  sulphuric  acid,  yields  a 
red  precipitate,  which  is  purified  by  re-crystallization  from  alcohol.  Purpurin 
thus  obtained  crystallizes  in  red  needles,  which  contain  Ci8H60g-{-2HO,  i.  e., 
2  eq.  of  carbon  less  than  alizarin.  When  treated  with  nitric  acid,  purpurin, 
like  alizarin,  furnishes  oxalic  and  phthalic  acids.  Purpurin  likewise  con- 
tributes to  the  tinctorial  properties  of  madder,  but  less  so  than  alizarin. 
Together  with  alizarin  and  purpurin,  several  other  substances  occur  in 
madder,  among  which  may  be  noticed  an  orange  pigment,  rubiacin,  convertible 
by  oxidizing  agents  into  a  peculiar  acid,  rubiacic  acid,  a  yellow  pigment, 
xanthin,  a  bitter  principle,  rubian,  sugar,  pectic  acid,  and  several  resins,  &c. 

Garancin  is  a  colouring  material,  which  is  produced  by  the  action  of  sul- 
phuric acid  upon  madder.  This  substance  possesses  a  higher  tinctorial  power 
than  madder  itself. 

The  beautiful  Turkey  red  of  cotton  cloth  is  a  madder-colour ;  it  is  given  by 
a  very  complicated  process,  the  theory  of  which  is  not  perfectly  elucidated. 
An  abstract  of  it  will  be  found  in  Prof.  Graham's  "  Elements  of  Chemistry." 

Safflower. — This  substance  contains  a  yellow  and  a  red  colouring  matter, 
the  latter  being  insoluble  in  water,  but  soluble  in  alkaline  liquids.  The  saf- 
flower may  be  exhausted  with  water  acidulated  with  acetic  acid,  and  the 
solution  mixed  with  acetate  of  lead,  and  filtered  from  the  dark-coloured 
impure  precipitate.  The  lead-compound  of  the  yellow  pigment  may  then  be 
thrown  down  by  addition  of  ammonia,  and  decomposed  by  sulphuric  acid. 
In  its  purest  form  the  yellow  matter  forms  a  deep  yellow,  uncrystallizable, 
and  very  soluble  substance,  very  prone  to  oxidation.  In  its  lead-compound 
it  has  probably  the  composition  03411,20,3. 

The  red  matter  or  carthamin  is  obtained  from  the  residual  saiflower  by  a 
dilute  solution  of  carbonate  of  soda ;  pieces  of  cotton  wool  are  immersed  in 
the  liquid,  and  acetic  acid  gradually  added.  The  dried  cotton  is  then  digested 
in  a  fresh  quantity  of  the  alkaline  solution,  and  the  liquid  supersaturated 
with  citric  acid,  which  throws  down  the  carthamin  in  carmine-red  flocks.  It 
forms,  when  pure  and  dry,  an  amorphous,  brilliant,  green  powder,  nearly 
insoluble  in  water,  but  soluble  in  alcohol  with  splendid  purple  colour.  It 
contains  C^^ll^O^. 

Brazil-wood  and  logwood  give  red  and  purple  infusions,  which  are  largely 
used  in  dyeing ;  the  colouring  principle  of  logwood  is  termed  hemaiozylinf 


RED    AND    YELLOW    DYES.  479 

and  has  been  obtained  in  crystals.  This  substance  contains  C4qH70,5-}-8HO, 
Acids  brighten  these  coloui's,  and  alkalis  render  them  purple  or  blue. 

Among  yellow  dyes,  quercitron-bark,  fustic-wood,  and  saffron  may  be  men- 
tioned, and  also  turmeric  ;  these  all  give  yellow  infusions  to  water,  and  furnish 
more  or  less  permanent  colours. 

Pwrree  or  Indian  yellow,  a  body  of  unknown  origin,  used  in  water-colour 
painting,  according  to  the  researches  of  Stenhouse  and  Erdmann,  is  a  com- 
poTind  of  magnesia  with  a  substance  termed  purreic  or  euxanthic  acid.  The 
latter,  when  pure,  crystallizes  in  nearly  colourless  needles,  sparingly  soluble 
in  cold  water,  and  of  sweetish  bitter  taste.  It  forms  yellow  compounds  with 
the  alkalis  and  earths,  and  is  decomposed  by  heat  with  production  of  a 
neutral  crystalline  sublimate,  pitrrenone  or  euxanthone.  Purreic  acid  contains 
C^gHjgOgi,  purrenone  0,311404.  By  the  action  of  chlorine,  bromine,  and  nitrio 
acid,  a  series  of  substitution-products  are  formed. 


Certain  of  the  products  of  the  action  of  nitric  acid  upop  aloes  resemble 
very  much  some  of  the  derivatives  of  indigo,  without,  however,  it  seems, 
being  identical  with  them.  Powdered  aloes,  heated  for  a  considerable  time 
with  excess  of  moderately  strong  nitric  "acid,  yields  a  deep  red  solution,  which 
deposits  on  cooling  a  yellow  crystalline  mass.  This,  purified  by  suitable 
means,  constitutes  chrysammic  acid;  it  crystallizes  in  golden-yellow  scales, 
which  have  a  bitter  taste,  and  are  but  sparingly  soluble  in  water.  Its  potassa- 
salt  has  a  carmine-red  tint,  and  exhibits  a  green  metallic  lustre,  like  that  of 
murexide.  The  formula  of  chrysammic  acid  is  not  perfectly  established.  It 
is  probably  Cj4HN20ii,HO.  Like  picric  acid,  "it  yields  with  chloride  of  lime, 
chloropicrin.  The  mother-liquor  from  which  the  chrysammic  acid  has  been 
deposited  contains  a  second  acid,  the  chrysolepic,  which  .also  forms  golden- 
yellow,  sparingly  soluble,  scaly  crystals.  The  potassa-salt  forms  small, 
yellow  prisms,  of  little  solubility.  It  explodes  by  heat.  Chrysolepic  acid 
contains  C,2H2N30,3,HO  ;  it  is  isomeric  and  possibly  identical  with  picric  acid. 

To  these  may  be  added  the  styphnic  acid  recently  described  by  MM. 
Boettger  and  Will,  produced  by  the  action  of  nitric  acid  of  sp.  gr.  1-2  upon 
assafcetida  and  several  ^tier  gum-resins  and  extracts.  Purree,  when  treated 
with  excess  of  nitric  acid,  likewise  yields  styphnic  acid.  It  crystallizes, 
when  pure,  in  slender,  yellowish-white  prisms,  sparingly  soluble  in  water, 
readily  dissolved  in  alcohol  and  ether.  It  has  a  purely  astringent  taste, 
and  stains  the  skin  yellow.  By  gentle  heat  it  melts,  and  on  cooling  becomes 
crystalline ;  suddenly  and  strongly  heated,  it  burns  like  gunpowder.  It  also 
furnishes  chloropicrin.  The  salts  of  this  substance  mostly  crystallize  in 
orange-yellow  needles,  and  explode  with  great  violence  by  heat.  Styphnic 
acid  contains  Ci2H2N30i5,HO,  i.  e.,  picric  acid-|-2  eq.  of  oxygen.  It  may  be 
viewed  as  a  nitro-substitute  of  the  same  acid,  CjgHgOjiHO,  which,  by  the  in- 
troduction of  chlorine  in  the  place  of  hydrogen,  furnishes  chloroniceic  acid 
(see  page  463). 

Hypothetical  niceic  acid Ci2H5,03,H0 

Chloroniceic  acid Ci2(H4Cl)03,HO 

Trinitroniceic  acid Ci2H2(N04)303,HO. 


480  OILSANDFATS. 


SECTION  VII 

OILS  AND  FATS. 


The  oils  and  fats  form  an  interesting  and  very  natural  group  of  substances, 
which  have  been  studied  with  great  success.  The  vegetable  and  animal  fats 
agree  so  closely  in  every  respect,  that  it  will  be  convenient  to  discuss  them 
under  one  head. 

Oily  bodies  are  divided  into  volatile  and  fixed:  the  former  are  capable  of 
being  distilled  without  decomposition,  the  latter  are  not.  When  dropped  or 
spread  upon  paper,  they  all  produce  a  greasy  stain ;  in  the  case  of  a  vola- 
tile oil,  this  stain  disappears  when  the  paper  is  warmed,  which  never  happens 
with  a  fixed  fatty  substance.  All  these  bodies  have  an  attraction,  more  or 
less  energetic,  for  oxygen :  this  in  some  cases  reaches  such  a  height  as  to 
occasion  spontaneous  inflammation,  as  in  the  instance  of  large  masses  of  cot- 
ton or  flax  moistened  with  rape  (ff  linseed  oil.  The  effect  of  this  absorption 
of  oxygen  leads  to  a  farther  classification  of  the  fixed  oils  into  drying  and 
non-drying  oils,  or  those  which  become  hard  and  resinous  by  exposure  to  air, 
and  those  which  thicken  slightly,  become  sour  and  rancid,  but  never  solidify. 
To  the  first  class  belong  the  oils  used  in  painting,  as  linseed,  rape,  poppy- 
seed,  and  walnut ;  and  to  the  second,  olive  and  palm-oils,  and  all  the  oils  and 
fats  of  animal  origin.  The  parts  of  plants  which  contain  the  largest  quanti- 
ties of  oil  are,  in  general,  the  seeds.  Olive-oil  is,  however,  obtained  from  the 
fruit  itself.  The  leaves  of  many  plants  are  varnished  on  their  upper  surface 
with  a  covering  of  waxy  fat.  Among  the  natural  orders,  that  of  the  crudfercR 
is  conspicuous  for  the  number  of  oil-bearing  species. 

The  fixed  oils  in  general  have  but  feeble  odour,  and  scarcely  any  taste ; 
irhenever  a  sapid  oil  or  fat  is  met  with,  it  is  invariably  found  to  contain  some 
volatile  oily  principle,  as  in  the  case  of  common  butter.  They  are  all  insolu- 
ble in  water,  and  but  slightly  soluble  in  alcohol,  with  the  exception  of  castor- 
oil  ;  in  ether  and  in  the  essential  oils,  on  the  other  hand,  they  dissolve  in 
large  quantity. 

The  consistence  of  these  substances  varies  from  that  of  the  thinnest  olive- 
oil  to  that  of  solid,  compact  suet;  and  this  difference  proceeds  from  the  vari- 
able proportions  in  which  the  proximate  solid  and  fluid  fatty  principles  are 
associated  in  the  natural  product.  All  these  bodies  may,  in  fact,  by  mere 
mechanical  means,  or  by  the  application  of  a  low  temperature,  be  separated 
into  two,  or  sometimes  three,  different  substances,  which  dissolve  in,  or  mix 
with  each  other,  in  all  proportions.  Thus,  olive  oil  exposed  to  a  cold  of 
40°  (4°-5C)  deposits  a  large  quantity  of  crystalline  solid  fat,  which  may  be 
separated  by  filtration  and  pressure ;  this  is  termed  margarin,  from  its  pearly 
aspect.  That  portion  of  the  oil  which  retains  its  fluidity  at  this,  or  even  an 
inferior  degree  of  cold,  has  received  the  name  olcin  or  elain.  Again,  a  solid 
animal  fat  may,  by  pressure  between  folds  of  blotting-paper,  be  made  much 
harder,  more  brittle,  and  more  difficult  of  fusion.  The  paper  becomes  im- 
pregnated with  a  permanently  fluid  oil,  or  olein,  while  the  solid  part  is  found 
to  consist  of  a  mixture  of  two  solid  fats,  one  resembling  the  margarin  of  olive- 


OILS     AND    FATS.  481 

oil,  and  the  other  having  a  much  higher  melting-point,  and  other  propertiei 
which  distinguish  it  from  that  substance ;  it  is  called  sfearin. 

Th-Bse  remarks  apply  to  all  ordinary  oils  and  fats :  it  is,  however,  by  no 
means  proved  that  the  olein  and  margarin  of  all  vegetable  and  animal  oils 
are  identical;  it  is  very  possible  that  there  may  be  essential  differences 
among  them,  more  especially  in  the  case  of  the  first-named  substance. 

Fixed  fatty  bodies,  in  contact  with  alkaline  solutions  at  a  high  tempera- 
ture, undergo  the  remarkable  change  termed  saponification.  When  stearin, 
margarin,  or  olein,  are  boiled  with  a  strong  solution  of  caustic  potassa  or 
soda,  they  gradually  combine  with  the  alkali,  and  form  a  homogeneous, 
viscid,  transparent  mass,  or  soap,  freely  soluble  in  warm  water,  although  in- 
soluble in  saline  solutions.  If  the  soap  so  produced  be  afterwards  decom- 
posed by  the  addition  of  an  acid,  the  fat  which  separates  is  found  completely 
changed  in  character ;  it  has  acquired  a  strong  acid  reaction  when  applied 
in  a  melted  state  to  test-paper,  and  it  has  become  soluble  with  the  greatest 
facility  in  warm  alcohol ;  it  is  in  fact  a  new  substance,  a  true  acid,  capable 
of  forming  salts,  and  a  compound  ether,  and  has  been  generated  out  of  the 
elements  of  the  neutral  fat  under  the  influence  of  the  base.  Stearin,  when 
thus  treated,  yields  stearic  acid,  margarin  gives  margaric  acid,  olein  gives 
oleic  acid,  and  common  animal  fat,  which  is  a  mixture  of  the  three  neutral 
bodies,  affords  by  saponification  by  an  alkali  and  subsequent  decomposition 
of  the  soap,  a  mixture  of  the  three  fatty  acids  in  question.  These  bodies 
are  not,  however,  the  only  products  of  saponification ;  the  change  is  always 
accompanied  by  the  formation  of  a  very  peculiar  sweet  substance,  called 
glycerin,  which  remains  in  the  mother-liquor  from  which  the  acidified  fat  has 
been  separated.  The  process  of  saponification  itself  proceeds  with  perfect 
facility  in  a  close  vessel ;  no  gas  is  disengaged ;  the  neutral  fat,  of  whatso- 
ever kind,  is  simply  resolved  into  an  alkaline  salt  of  the  fatty  acid,  or  soap, 
and  into  glycerin.' 

Stearin  and  stearic  acid.  —  Pure  animal  stearin  is  most  easily  obtained 
by  mixing  pure  mutton-fat,  melted  in  a  glass  flask,  with  several  times  its 
weight  of  ether,  and  suftering  the  whole  to  cool.  Stearin  crystallizes  out, 
while  margarin  and  olein  remain  in  solution.  The  soft  pasty  mass  may  then 
be  transferred  to  a  cloth,  strongly  pressed,  and  the  solid  portion  still  farther 
purified  by  re-crystallization  from  ether.  It  is  a  white  friable  substance,  in- 
soluble in  water,  and  nearly  so  in  cold  alcohol ;  boiling  spirit  takes  up  a 
small  quantity.  Boiling  ether  dissolves  it  with  great  ease,  but  when  cold 
retains  only  g^T.  of  its  weight.  The  meltiug-point  of  pure  stearin,  which  is 
one  of  its  most  important  physical  characters,  may  be  placed  at  about  130° 
(oi°-5C). 

When  stearin  is  saponified,  it  yields,  as  already  stated,  glycerin  and  stearic 
acid.  The  latter  crystallizes  from  hot  alcohol  in  milk-white  needles,  which 
are  inodorous,  tasteless,  and  quite  insoluble  in  water.  It  dissolves  in  its 
oTvn  weight  of  cold  alcohol,  and  in  all  proportions  at  a  boiling  heat ;  it  is 
likewise  soluble  in  ether.  Alkaline  carbonates  are  decomposed  by  stearic 
acid.  Exposed  to  heat,  it  fuses,  and  at  a  higher  temperature,  if  air  be  ex- 
cluded, volatilizes  unchanged.  The  melting-point  of  stearic  acid  is  about 
158°  (70°C). 

Margarin  and  margaric  acid.  —  The  ethereal  mother-liquor  from  which 
stearin  has  separated  in  the  process  just  described  yields  on  evaporation  a 
soft-solid  mixture  of  margarin  and  olein  with  a  little  stearin.     By  compres- 

'  We  are  indebted  to  M.  Chevreul  for  the  first  series  of  scientific  researches  on  the  fixed 
oils  and  fats,  and  on  the  theory  of  saponification.  These  admirable  investigations  are  detailed 
in  the  early  volumes  of  the  '•  Annales  de  Chimie  et  de  Physique,"  and  were  afterwards  pub- 
liphed  in  a  peparat**  form  in  1823,  under  the  title  of  '•  Eccherchet  chimiquit  sur  let  Corpt  grot 
dfOriffive  animale." 
41 


482  OILS     AND     FATS. 

sion  between  folds  of  blotting-paper,  and  re-solution  in  ether,  it  is  rendere<* 
tolerably  pure.  lu  this  state  margarin  very  much  resembles  stearin ;  it  is 
however,  more  fusible,  melting  at  116°  (46°-GC),  and  very  much  more  solu- 
ble in  cold  ether.  By  saponification  it  yields  glycerin  and  margaric  acid. 
The  properties  of  this  last-named  substance  resemble  in  the  closest  manne? 
those  of  stearic  acid ;  it  is  different  in  composition,  however,  more  solubl* 
in  cold  spirit,  and  has  a  lower  melting-point,  viz.,  140°  (60°C)  or  there- 
abouts.    Its  salts  also  resemble  those  of  stearic  acid. 

A  more  or  less  impure  mixture  of  stearic  and  margaric  acids  is  no^ 
very  extensively  used  as  a  substitute  for  wax  and  spermaceti  in  the  manu- 
facture of  candles.  It  is  prepared  by  saponifying  tallow  by  lime,  decom- 
posing the  insoluble  salt  so  formed  by  boiling  with  dilute  sulphuric  acid,  and 
then  pressing  out  the  fluid  or  oily  portion  from  the  acidified  fat. 

The  solid  part  of  olive-oil  is  said  to  be  a  definite  compound  of  true  mar- 
garin and  olein,  inasmuch  as  its  melting-point,  68°  (20°C),  is  constant;  it 
gives  by  saponification  a  mixture  of  margaric  and  oleic  acids. 

Olein  and  oleic  acid. — It  is  doubtful  whether  a  perfectly  pure  oleln  has 
yet  been  obtained ;  the  separation  of  the  last  portions  of  margarin,  with 
which  it  is  always  naturally  associated,  is  a  task  of  extreme  difficulty.  Any 
fluid  oil,  animal  or  vegetable,  which  has  been  carefully  decolorized,  and 
filtered  at  a  temperature  approaching  the  freezing-point  of  water,  may  be 
taken  as  a  representative  of  the  substance.  Oleic  acid  much  resembles  olein 
in  physical  characters,  being  colourless  and  lighter  than  water,  but  it  has 
visually  a  distinct  acid  reaction,  a  sharp  taste,  and  is  miscible  with  alcohol 
in  all  proportions.  "When  submitted  to  the  action  of  nitric  acid,  it  yields 
almost  the  whole  series  of  acids,  of  which  formic,  acetic,  propionic,  butyric, 
&c.,  are  members,  and  which  has  been  mentioned  in  a  previous  section  of 
this  work  (see  page  395). 

When  stearic  or  margaric  acid,  or  ordinary  animal  fats,  are  exposed  to 
destructive  distillation,  they  yield  margaric  acid,  a  fatty  body  incapable  of 
saponification,  termed  margarone,  a  liquid  carbide  of  hydrogen,  and  various 
permanent  gases.  The  neutral  fats  furnish  besides  an  extremely  pungent 
and  even  poisonous,  volatile  principle,  called  acrolein,  described  farther  on. 

In  the  manufacture  of  ordinary  soaps  both  potassa  and  soda  are  used  ;  the 
former  yielding  so//,  and  the  latter  hard  soaps.  Animal  and  vegetable  fats 
are  employed  indifferently,  and  sometimes  resin  is  added. 

Coviposition  of  the  preceding  Substances. — The  following  are  the  formulae  at 
present  assigned  to  the  fatty  acids  in  question :  they  are  chiefly  founded  on 
investigations  made  at  Giessen. 


Margaric  is  thus  seen  to  differ  from  stearic  acid  in  containing  1  eq.  of  oxy- 
gen more,  and  stearic  acid  can  actually  be  converted  into  margaric  by  the 
action  of  oxidizing  agents.  Stearic  acid  is  bibasic,  and  in  its  crystallized 
state  contains  2  eq.  of  water.  Margaric  acid,  as  represented  by  the  above 
formula,  is  likewise  bibasic,  but  many  chemists  consider  it  as  a  monobasic 
acid  034113303,110 ;  its  bibasic  nature  being,  in  fact,  by  no  means  so  we'.l 
established  as  that  of  stearic  acid.  The  subject  requires  farther  examina- 
tion, especially  since  an  opinion  has  lately  been  expressed,  that  stearic  and 
margaric  acids  are  isomeric  modifications  of  the  same  acid.' 

*  According  to  Iluntz,  mnrgraric  ndd  is  a  mixture  of  rtearic  and  palmitic  acids,  and  tli^t 
one  part  of  stearic  acid  mixed  with  9-10  parts  of  palmitic  acid  (meltinj^at  144°;  62°-2C),  pro- 
duced a  compound  fusing  at  140°  (_€0°C),  and  pos.^es.'sing  all  the  properties  and  ultimate  com- 
position of  margaric  acid.  Moteover,  when  margaric  acid  obtained fi-om  mutton-fat  was  actal 
OTi  by  acetate  of  baryta,  the  firtt  precipitate  gave  an  acid  melting  at  136°-5  (57°C),  and  soliii- 


OILS    AND    FATS.  483 

OUic  acid  fi'om  almond-oil,  butter,  and  beef-suet,  gave  results  agreeing 
pi.6tt^  f^rell,  and  leading  to  the  formula  035113303,110,  the  oleic  acid  of  goose- 
hxi,  nnd  olive-oil,  having  the  same  composition.  Former  researches  had  led 
to  different  results  which  are  explained  by  the  extreme  proneness  to  oxida- 
tion of  the  substauce  itself.  The  oleic  acid  obtained  from  linseed-oil  appears 
to  differ  from  the  preceding  substance ;  its  analysis  having  led  to  the  for- 
mula C46H3s05,HO.  (?) 

Margarone  probably  contains  CjsHjgO,  or  margaric  acid  minus  1  eq.  of 
carbonic  acid. 

The  composition  of  stearin,  margarin,  and  oleine  is  most  safely  deduced 
from  a  comparison  of  that  of  the  acids  to  which  they  give  rise,  and  of  gly- 
cerin, 

Margaric,  stearic,  and  oleic  acids  have  many  properties  in  common  ;  their 
salts  much  resemble  each  other,  those  of  the  alkalis  being  soluble  in  pure 
water  when  warm,  but  not  in  saline  solution.  A  large  quantity  of  cold  water 
added  to  an  alkaline  margarate  or  stearate  occasions  the  separation  of  a 
crystalline,  insoluble  acid  salt.  The  margarates,  stearates,  and  oleates  of 
lime,  baryta,  and  the  oxides  of  the  metals  proper  are  insoluble  in  water. 
They  are  easily  obtained  by  double  decomposition,  and  in  some  few  cases  by 
direct  action  on  the  neutral  fat.  A  solution  of  soap  in  alcohol  is  sometimes 
used  as  a  test  for  the  presence  and  quantity  of  lime,  &c.,  in  waters  under 
examination  (see  page  241). 

Glycerin. — This  substance  is  very  readily  obtained  by  heating  together 
olive  or  other  suitable  oil,  protoxide  of  lead,  and  water,  as  in  the  manufacture 
of  common  lead-plaster ;  an  insoluble  soap  of  lead  is  formed,  while  the  gly- 
cerin remains  in  the  aqueous  liquid.  The  latter  is  treated  with  sulphuretted 
hydrogen,  digested  with  animal  charcoal,  filtered,  and  evaporated  in  vacuo 
at  the  temperature  of  the  air.  In  a  pure  state,  glycerin  forms  a  nearly  colour- 
less and  very  viscid  liquid,  of  sp.  gr.  1-27,  which  cannot  be  made  to  crystal- 
lize. It  has  an  intensely  sweet  taste,  and  mixes  with  water  in  all  propor- 
tions ;  its  solution  does  not  undergo  the  alcoholic  fermentation,  but  when 
mixed  with  yeast  and  kept  in  a  warm  place,  it  is  gradually  converted  into 
propionic  acid  (see  page  377).  Glycerin  has  neither  basic  nor  acid  proper- 
ties. Exposed  to  heat,  it  volatilizes  in  part,  darkens,  and  becomes  destroyed, 
one  of  its  products  of  destruction  being  a  substance  possessing  a  most  power- 
fully penetrating  odour,  which  is  called  acrolein  (see  page  345).  Nitric  acid 
converts  it  into  oxalic  acid. 

Glycerin  is  composed  of  CgHgOg. 

Glycerin  combines  with  the  elements  of  sulphuric  acid,  forming  a  compound 
acid,  the  sulphogly eerie,  €611705,2803, HO,  which  gives  soluble  salts  with  lime, 
baryta,  and  protoxide  of  lead.' 

Palm  and  cocoa  oils. — These  substances,  which  at  the  common  tempera- 
ture of  the  air  have  a  soft-solid  or  buttei-y  consistence,  are  now  largely  con- 
sumed in  this  country.  Palm-oil  is  the  produce  of  the  Elais  guianeiuis,  and 
comes  chiefly  from  the  coast  of  Africa.  It  has,  when  fresh,  a  deep  orange- 
red  tint,  and  a  very  agreeable  odour ;  the  colouring  matter,  the  nature  of 

fied  without  crystallizing ;  the  other  one,  after  repeated  crystallization,  melted  at  142°'7  (61°*6 
C).  crystallized  in  needles,  and  exhibited  the  properties  of  palmitic  acid.  — R.  B. 

*  Glycerin  has  been  combined  with  acid.".  To  effect  this,  the  acid  is  mixed  with  the  glyce- 
rin, and  a  current  of  hydrochloric  acid  passed  through  the  mixture  for  several  hours.  This 
Is  set  aside  for  periods,  varying  from  a  few  days  to  several  weeks.  The  hydrochloric  acid  is 
saturated  by  carbonate  of  soda,  and  then  washed  repeatedly. 

These  compounds  are  oleaginous,  nearly  or  quite  insoluble  in  water,  do  not  unite  with 
carbonated,  but  are  slowly  decomposed  by  caustic  alkali,  the  glycerin  separating  unaltered. 

Acetate  of  glycerin  (acetine)  has  the  appearance  of  a  limpid,  colourless  oil,  of  a  taste,  at 
first,  swetit,  then  sharp,  the  odour  of  acetic  ether,  and  is  volatile,  without  decomposition. 

Valerate  of  glycerin  (valerene)  resembles  phoceuine,  with  which  it  should  be  ideuiicaL 

Benzoate  of  glycerin  (bea'ioicine;  has  an  aromatic  and  peppery  taate.  —  R.  B. 


484  OILS    AND    FATS. 

"Which  is  unknown,  is  easily  destroyed  by  exposure  to  light,  especially  at  r 
high  temperature,  and  also  by  oxidizing  agents.  The  oil  melts  at  80°  (26° -6 
C).  By  cautious  pressure  it  may  be  separated  into  a  fluid  olein  and  a  solid 
substance,  palmitin,  which,  when  purified  by  crystallization  from  hot  ether, 
is  perfectly  white,  fusible  at  118°  (47° -80),  soluble  to  a  small  extent  only  in 
boiling  alcohol,  and  convertible  by  saponification  into  palmitic  acid.  The  latter 
resembles  in  the  closest  manner  margaric  acid,  and  has  the  same  melting- 
point;  it  differs  in  composition,  however,  containing  H32C3,03,IIO.  By  keep- 
ing, palm-oil  seems  to  sufi'er  a  change  similar  to  that  produced  by  saponifi- 
fication;  in  this  state  it  is  found  to  contain  traces  of  glycerin,  and  a 
considerable  quantity  of  oleic  acid,  together  with  a  solid  fatty  acid,  first 
supposed  to  be  margaric,  which  is  probably  palmitic  acid.  The  oil  becomes 
harder  and  rancid,  and  its  melting-point  is  raised  at  the  same  time.  Cocoa- 
oil,  extracted  from  the  kernel  of  the  common  cocoa-nut,  is  white,  and  has  a 
far  less  agreeable  smell  than  the  preceding.  It  contains  olein  and  a  solid  fat, 
often  used  as  a  substitute  for  tallow  in  making  candles,  which  by  saponifica- 
tion gives  a  crystallizable  fatty  acid,  cocinic  acid,  having  the  usual  properties 
of  these  bodies,  and  melting  at  95°  (35°-5C).  It  is  composed  of  C26H2503,HO. 
Both  this  and  palmitic  acid  are  monobasic. 

The  solid  vegetable  fat  from  the  Myristica  moschata  contains  a  volatile  oil, 
a  fluid  olein,  and  a  solid,  crystallizable,  fatty  principle  ;  this,  when  saponified, 
which  occurs  with  difficulty,  yields  myristic  acid.  This  substance  has  been 
examined  by  Dr.  Playfair ;  it  melts  at  120°  (48°'8C),  and  contains  CagHa^Oj, 
HO.     It  is  monobasic. 

Cacao-butter,  extracted  from  the  crushed  beans  by  boiling  with  water, 
yields  by  saponification  a  fatty  acid,  identical,  according  to  Dr.  Stenhouse, 
with  the  stearic  acid  from  animal  fat, 

Elaidin  and  elaidic  acid. — When  olive-oil  is  mixed  with  a  small  quantity 
of  nitrous  acid,  nitric  acid  containing  that  substance,  or  solution  of  nitrate 
of  mercury  made  in  the  cold,  it  becomes  after  a  few  hours  a  yellowish,  soft- 
solid  mass,  which,  pressed  and  treated  with  alcohol,  furnishes  a  peculiar 
white,  crystalline,  fatty  substance,  termed  elaidin.  It  resembles  a  neutral 
fat  in  properties,  melts  at  90°  (32°-2C),  dissolves  with  difficulty  in  boiling 
alcohol,  easily  in  ether,  and  is  resolved  by  saponification  into  glycerin  and 
elaidic  acid,  which  much  resembles  margaric  acid.  Oleic  acid  is  directly  con- 
vertible by  nitrous  acid  into  elaidic  acid.  It  is  not  every  kind  of  oil  which 
furnishes  elaidin :  the  drying  oils,  as  those  of  linseed,  poppy-seed,  walnuts, 
&c.,  refuse  to  solidify;  almonds,  olive,  and  castor-oils  possess  the  property 
in  a  high  degree. 

Elaidic  acid  appears  to  have  the  same  composition  as  oleic  acid,  or  CoflH,, 
O3.HO. 

Suberic,  sticcintc,  and  sebacic  acids. — Suberic  acid  has  long  been  known 
as  a  product  of  the  oxidation  of  cork  by  nitric  acid  (see  page  345)  ;  succinic 
acid  is  obtained  by  the  dilution  of  amber,  a  fossil  resin.  Recently  both  have 
been  produced  by  the  long-continued  action  of  nitric  acid  upon  stearic  and 
margaric  acids.  Suberic  acid  is  a  white,  crystalline  powder,  sparingly  so- 
luble in  cold  water,  fusible  and  volatile  by  heat;  it  contains  C,gH,20g,2HO. 
Succinic  acid  forms  regular,  colourless  crystals,  soluble  in  5  parts  of  cold, 
and  in  half  that  quantity  of  boiling  water;  it  is  also  fusible  and  volatile 
without  decomposition,  and  contains  CgH40jj,2nO.  The  remarkable  pro- 
duction of  this  substance  from  malic  acid  by  a  process  of  fermentation  has 
been  already  mentioned  (see  page  415).  Sebacic  acid  is  a  constant  product 
of  the  destructive  distillation  of  oleic  acid,  olein,  and  all  fatty  substances 
containing  ttose  bodies;  it  is  extricated  by  boiling  the  distilled  matter  with 
water  ;  it  h,ts  also  been  lately  formed  by  the  action  of  potassa  on  castor  oil 
(see  page  488).     It  forms  small  pearly  crystals  resembling  those  of  benzoic 


OILS     AND    FATS.  485 

ft'^ifl.  It  has  a  faint  acid  taste,  is  but  little  soluble  in  cold  water,  melts  when 
heated,  and  sublimes  unchanged.  Sebacic  acid  is  composed  of  CigHgOj,!!© 
or  C2,U,,0„2l{0. 

Butter  ;  volatile  acids  of  butter. — Common  butter  chiefly  consists  of 
a  solid  crj^stallizable,  and  easily  fusible  fat,  a  fluid  oily  substance,  and  a 
yellow  colouring  matter,  besides  mechanical  impurities,  as  casein.  The  oily 
part  appears  to  be  a  mixture  of  olein  and  a  peculiar  odoriferous  fatty  prin- 
ciple, butyrin,  not  yet  isolated,  which  by  saponification  yields  fbur  distinct 
volatile  acids,  the  butyric,  the  caproic,  the  caprylic,  and  the  capric :  these  are 
most  easily  obtained  by  saponifying  butter  with  potassa  or  soda,  adding  an 
excess  of  sulphuric  acid,  and  distilling.  The  acid  watery  liquid  obtained 
may  then  be  saturated  with  an  alkali,  evaporated  to  a  small  bulk,  and  then 
distilled  with  excess  of  sulphuric  or  phosphoric  acid  in  a  retort.  The  mixed 
acids  are  separated  by  taking  advantage  of  the  unequal  solubility  of  their 
baryta-salts ;  the  less  soluble  salts  of  the  mixture,  amounting  to  about  J^ 
of  the  whole  mass,  contain  capric  and  caprylic  acids ;  the  larger  and  more 
soluble  portion,  the  caproic  and  butyric  acids. 

Butyric  acid,  when  pure,  is  a  thin  colourless  liquid,  of  pungent  rancid 
odour  and  sour  taste.  It  is  miscible  in  all  proportions  with  water  and  alcohol. 
Its  density  is  0-963,  and  it  boils  and  distils  unchanged  at  327°  (164°C).  It 
is  attacked  by  chlorine,  with  production  of  oxalic  acid  and  of  a  chlorinetted 
compound  not  examined.     Butyric  acid  contains  CgH^OsjHO. 

Caproic  acid  forms  a  colourless  liquid,  of  sp.  gr.  0-922,  boiling  at  388<»-4 
(198°C) ;  it  has  a  feeble  odour,  somewhat  resembling  that  of  acetic  acid,  Kud 
is  much  less  soluble  in  water  than  butyric  acid.  It  contains  CjjHuOj.HO. 
The  artificial  formation  of  this  acid  from  cyanide  of  amyl  has  been  already 
noticed  (see  page  390).  Caproic  acid  has  been  lately  submitted  to  the  action 
of  the  galvanic  current.  Messrs.  Brazier  and  Gossleth  have  proved  that  it 
is  analogous  to  that  of  valeric  acid,  and  that  the  principal  product  is  the  hydro- 
carbon amyl  CjqHi,  previously  obtained  by  Dr.  Frankland  by  the  action  of 
zinc  upon  iodide  of  amyl  (see  page  390). 

Caprylic  acid  is  chiefly  remarkable  for  exhaling  a  powerful  and  disgusting 
odour  of  perspiration.  It  contains  CjgHj-OgJIO.  This  acid  has  been  lately 
obtained  by  a  very  interesting  reaction,  namely,  by  the  oxidation  of  the  new 
caprylic  alcohol  discovered  by  M.  Bonis  among  the  products  of  decomposition 
of  castor  oil  (see  page  488). 

Capric  acid  much  resembles  the  caproic  ;  it  has  a  mixed  odour  of  acetic 
acid  and  the  smell  of  the  goat,  and  is  very  sparingly  soluble  in  water.  Ita 
formula  is  CjoHigOg.HO. 

The  simple  relation  existing  between  the  formulae  of  the  volatile  acids  of 
butter,  which  are  all  members  of  the  series  of  fatty  acids,  has  been  already 
pointed  out  (see  page  395). 

These  acids  exist  ready  formed  in  rancid  butter  and  in  cheese,  associated 
with  valeric  acid.  They  are  produced  in  small  quantity  by  the  saponifica- 
tion of  most  animal  and  some  vegetable  fats,  and  are  generated,  as  has  been 
mentioned  already  (see  page  482),  together  with  other  products,  by  the 
action  of  nitric  acid  upon  oleic  acid.  Butyric  acid  has  been  observed  also 
as  a  product  of  the  spontaneous  decomposition  of  fibrin,  and  pre-exists  in  the 
leguminous  fruit  known  as  St.  John's  bread. 

Whale  and  seal  oil  yield  by  saponification  a  volatile  acid  greatly  resembling 
the  preceding,  called  phocenic  or  delphinic  acid;  it  was  formerly  believed  to 
be  a  peculiar  acid,  but  it  is  according  to  recent  experiments  nothing  but 
valeric  acid. 

Butyric  acid  has  acquired  a  certain  degree  of  importance  from  the  curioua 
discovery  of  M.  Pelouze,  that  sugar,  under  particular  circumstances,  is  sus- 
ceptible of  becoming  converted  into  that  substance.     A  tolerably  strong 
41* 


486  OILS    AND     FATS. 

solution  of  common  sugar  mixed  with  a  small  quantity  of  casein  and  gome 
chalk,  and  exposed  for  some  time  to  a  temperature  of  95°  (35°C),  yields, 
by  a  species  of  fermentation,  in  which  the  casein  is  the  active  ferment,  a 
large  amount  of  butyrate  of  lime ;  carbonic  acid  and  hydrogen  gases  are 
extricated  during  the  whole  period.     This  change  may  be  thus  expressed — 

C24H28O28    =     4HO-f8H-f8CO,     -I-     2(C8H703,HO) 

Grape-sugar.  Butyric  acid. 

The  mixture  directed  for  lactic  acid  answers  well  (see  page  350)  ,•  lactate 
of  lime  is  first  formed  in  large  quantity,  and  afterwards  gradually  dissolved 
and  converted  into  butyrate,  which  may  be  decomposed  by  sulphuric  acid 
and  distilled.  This  is  an  exceedingly  interesting  case  of  the  hftlf-artificial 
formation  of  an  animal  product. 

Wax.  —  Common  bces-xvax,  freed  from  its  yellow  colouring  matter  by 
bleaching,  may  be  separated  by  boiling  alcohol  into  two  different  proximate 
principles,  cerin  and  myricin.  The  first  is  a  white  crystalline  substance, 
soluble  in  about  16  parts  of  boiling  spirit,  and  melting  at  144°  (62°-2C) :  it 
is  the  more  abundant  of  the  two.  It  is  easily  saponified  by  a  solution  of 
caustic  potassa.  According  to  Brodie's  valuable  experiments  it  consists 
chiefly  of  cerotic  acid  Cg^IIggOgjHO,  which  belongs  to  the  series  of  fatty 
acids  (see  page  395).  The  same  body  in  a  very  interesting  form  of  combi- 
nation exists  in  Chinese  wax,  which,  according  to  Brodie,  is  a  compound 
ether  containing  cerotic  acid  combined  with  the  ether  of  cerotylic  alcohol 
€5411550,110.  It  may  be  viewed  as  cerotate  of  oxide  of  cerotyl  C34H55O, 
C54H53O3  corresponding  to  the  acetic  ether  of  the  wine-alcohol-series.  When 
heated  with  potassa  it  undergoes  the  changes  peculiar  to  compound  ethers, 
yielding  on  the  one  hand  cerotate  of  potassa,  and  on  the  other  hand  cerotylic 
alcohol.  Myricin  is  very  much  less  soluble  in  alcohol,  and  rather  more 
fusible.  It  is  saponified  with  difficulty  by  a  dilute  solution  of  caustic 
potassa,  palmitic  acid  CgjHgiOg.HO  (see  page  484),  combines  with  the  po- 
tassa, and  a  substance  CggHgiOjUO,  belonging  to  the  series  of  alcohols,  is 
set  free,  which  has  been  termed  melissic  alcohol.  Hence  myricin  is  like- 
wise a  compound  ether,  namely,  palmitate  of  oxide  of  melissyl  ^^^0^^=. 

Spermaceti. — The  soft-solid  matter  found  in  very  large  quantity  in  a 
remarkable  cavity  in  the  head  of  the  spermacetic  whale,  when  submitted  to 
pressure,  yields,  as  is  well  known,  a  most  valuable  fluid  oil,  and  a  crystal- 
line, brownish  substance,  which,  when  purified,  becomes  the  beautiful  snow- 
white  article  of  commerce,  spermaceti.  This  substance  appears,  by  the 
most  recent  experiments,  to  be  a  neutral  fatty  body  of  the  constitution  of 
compound  ethers,  and  not,  as  formerly  supposed,  a  mixture  of  several  proxi- 
mate principles.  It  melts  at  120°  (48°  BC),  and  when  cooled  under  favour- 
able circumstances,  forms  distinct  crystals.  Boiling  alcohol  dissolves  it  in 
small  quantity,  and  ether  in  much  larger  proportion.  Spermaceti  is  sapo- 
nifie*'  with  great  difficulty :  two  products  are  obtained,  a  substance  C32H34O2 
belonging  to  the  series  of  alcohols  (see  page  394),  to  which  the  name  cetylic 
{ethalic)  alcohol  has  been  given,  and  cetylic  [ethalic)  acid  C32H32O4  ;  the  first  is 
a  crystallizable  fat,  whose  melting-point  is  nearly  the  same  as  that  of 
spermaceti  itself,  but  its  solubility  in  alcohol  is  much  greater ;  it  is  also 
readily  sublimed  without  decomposition.  Cetylic  acid  stands  to  cetylic 
alcohol  in  the  same  relation  as  acetic  acid  to  ordinary  alcohol,  and  may  be 
actually  procured  from  the  latter  by  oxidation  ;  it  resembles  in  many  re- 
Bpects  margaric  acid.  By  oxidation  by  nitric  acid,  spermaceti  yields  a  large 
(ruantity  of  succinic  acid. 
*  Spermaceti  is  compoued  of  ^^^^QfPi=^^^^i^^^^O,C'y^\{^yO^;    it  is  cetylate  of 


OILS    AND    FATS.  487 

oxide  of  cetyl,  and  represents  in  the  cetyl-series  the  acetic  ether  of  the 

common  alcohol-series.' 

Cholesterin. — This  substance  is  found  in  small  quantity  in  various  parts 
of  the  animal  system,  as  in  the  bile,  in  the  brain  and  nerves,  and  in  the 
blood ;  it  forms  the  chief  ingredient  of  biliary  calculi,  from  which  it  is  easily 
extracted  by  boiling  the  powdered  gall-stones  in  strong  alcohol,  and  filtering 
the  solution  while  hot ;  on  cooling,  the  cholesterin  crystallizes  in  brilliant, 
colourless  plates.  It  has  the  characters  of  a  fat,  is  insoluble  in  water,  taste- 
less and  inodorous  ;  it  is  freely  soluble  in  boiling  water,  and  also  in  ether. 
It  altogether  resists  saponification.  Cholesterin  melts  at  278"  (136°C),  and 
contains  probably  C26H220- 

Cantharidin,  the  active  principle  of  the  Spanish  fly,  may  be  here  men- 
tioned. It  is  a  colourless,  crystallizable,  fatty  body,  extracted  by  ether  or 
alcohol  from  the  insect ;  it  is  insoluble  in  water  and  dilute  acids,  and  vola- 
tile when  strongly  heated.  The  vapour  attacks  the  eyes  in  a  very  painful 
manner.     Cantharidin  contains  C,oH6^4. 

Acrolein.  —  When  a  neutral  fat  is  subjected  to  destructive  distillation,  it 
furnishes,  as  already  mentioned,  among  other  products,  an  excessively  vola- 
tile acrid  substance,  which  attacks  the  eyes  and  the  mucous  membrane  of 
the  nose  most  distressingly.  As  the  neutral  fats  alone  yield  this  body,  and 
the  fatty  acids  never,  it  is  known  to  arise  from  the  elements  of  the  glycerin ; 
and  glycerin  itself  under  certain  circumstances  may  be  made  to  produce 
acrolein  abundantly.  It  is  best  prepared  by  distilling  glycerin  with  bisul- 
phate  of  potassa ;  both  the  preparation  and  purification  are  attended  with 
great  difficulties. 

Pure  acrolein  is  a  thin,  colourless,  highly  volatile  liquid,  lighter  than 
water,  and  boiling  at  126°  (o2°-9C).  Its  vapour  is  irritating  beyond  descrip- 
tion. It  is  sparingly  soluble  in  water,  freely  in  alcohol  and  ether.  Accord- 
ing to  M.  Redtenbacher  it  contains  Qf^^fi^. 

When  exposed  for  some  time  to  the  air,  or  when  mixed  with  oxide  of 
silver,  acrolein  oxidizes  with  avidity,  and  passes  into  acrylic  acid,  which  re- 
sembles in  very  many  particulars  acetic  and  propionic  acids;  it  contains 
CgHgOjjHO.  Acrolein  by  keeping  undergoes  partial  decomposition,  yielding 
a  white,  flocculent,  indifferent  body,  disacryle ;  the  same  substance  is  some- 
times produced  together  with  acrylic  acid  by  exposure  to  the  air.  In  con- 
tact with  alkalis,  acrolein  suffers  violent  decomposition,  producing,  like 
aldehyde,  a  resinous  body. 

The  action  of  sulphuric  acid  upon  olive-oil  has  been  studied  by  M.  Fr^my. 
When  the  oil  is  slowly  and  cautiously  mixed  with  half  its  volume  of  concen- 
trated sulphuric  acid,  all  rise  of  temperature  being  avoided,  a  homogeneous 
liquid  is  obtained,  which,  when  mixed  with  a  little  water,  separates  into  two 
layers,  the  undermost  consisting  of  sulpho-glyceric  and  free-sulphuric  acid, 
and  the  upper  and  syrupy  portion  of  two  compound  acids,  the  mlphomargaric 
and  sulpholeic.  These  latter  dissolve  in  a  large  quantity  of  water,  but  after 
some  time  undergo  decomposition  into  sulphuric  acid  and  several  new  fatty 
acids,  to  which  the  names  metamargaric,  hydromargaric,  hydromargaritic, 
meioleic,  and  hydroleic  were  given.     The  first  three  are  derived  from  the  ele- 

*  According  to  the  investigations  of  Ileintz,  the  composition  of  spermaceti  is  of  a  very 
co0-plex  character,  consisting  of  a  series  of  acids  differing  in  constitution  by  C2H2  combineU 
with  ethal.  viz. : — 

Margetlial    =  margarate  of  oxide  of  cetyl C34H330a,C32irs30 

Palmethai    =  palmitate C32n.,,03,C3-.H330 

Cetcthal        =  cetate CsoHMCii.CsaHaaO 

Myristethal  =  myriftate On8H270!),Cs2n3sO 

Cocethal       -=  cociuate C2tiH2sOa,Cx.H330.— R.  B, 


488  OILS     AND     PATS. 

ments  of  the  sulphomargaric  acid ;  they  are  solid  and  crystallizable,  and 
much  resemble  ordinary  margaric  acid,  diflfering  slightly  from  that  substance 
and  from  each  other  in  their  melting-points,  degree  of  solubility  in  alcohol, 
&c.  The  metoleic  and  hydi-oleic  acids  are  fluid,  and  are  derived  ft-om  the 
eulpholeic  acid  of  the  mixture.  They  yield  carbonic  acid  and  liquid  hydro- 
carbons by  destructive  distillation.  The  composition  of  these  fatty  acids  is 
yet  uncertain,  but  in  all  probability  they  only  differ  from  margaric  and  oleic 
acids  by  the  elements  of  water.  The  action  of  sulphuric  acid  upon  the  oil 
is  thus  somewhat  similar  to  the  effect  of  saponification,  the  neutral  fat  being 
resolved  into  margaric  and  oleic  acids  and  glycerin,  the  whole  of  which 
then  combine  with  the  elements  of  sulphuric  acid  to  form  compounds  belong- 
ing to  the  large  group  of  substances  of  which  sulphovinic  acid  is  the  typical 
member. 

The  sulphuric  saponification  of  fatty  bodies  is  now  carried  out  on  &  very 
large  scale  for  producing  cheaper  varieties  of  ^'stearin  candles."  For  this 
purpose,  inferior  fatty  bodies,  such  as  palm-oil,  are  mixed  with  5  or  6  per 
cent,  of  concentrated  sulphuric  acid,  and  exposed  to  a  temperature  of  350" 
(177°C)  produced  by  overheated  steam.  After  cooling,  the  black  mass  thus 
obtained  crystallizes  to  a  tolerably  solid  fat,  which  is  washed  once  or  twice 
with  water,  and  then  submitted  to  distillation  by  the  aid  of  steam,  heated  to 
about  560°  (293° -50).  The  product  of  the  distillation,  which  is  beautifully 
white,  may  be  at  once  used  for  making  candles ;  frequently,  however,  it  un- 
dergoes the  processes  of  cold  and  hoi  pressing,  whereby  a  much  more  solid 
fat  is  obtained. 

Castor  oil,  which  differs  in  some  respects  from  the  ordinary  vegetable 
oils,  yields,  by  oxidation  with  nitric  acid,  a  peculiar  product,  namely,  a  vola- 
tile fatty  acid  to  which  the  term  cenanlhylic  has  been  applied.  It  forms  a 
colourless,  oily  liquid  of  aromatic  odour  and  burning  taste,  and  slightly 
soluble  in  water.  It  refuses  to  solidify  at  a  very  low  temperature,  and  can- 
not be  distilled  alone  without  some  decomposition,  although  its  vapour  passes 
over  readily  with  that  of  water.  This  body  has  distinct  acid  properties, 
forms  a  series  of  salts  and  an  ether,  and  contains  €,411,303, HO.  Under  the 
influence  of  the  galvanic  current  it  undergoes  a  decomposition  similar  to 
that  of  valeric  acid,  according  to  Messrs,  Brazier  and  Gossleth,  the  principal 
product  being,  together  with  a  hydrocarbon  containing  equal  equivalents  of 
carbon  and  hydrogen,  an  oily  substance  CjgHig,  boiling  at  395''-6  (202°C),  to 
which  the  name  caprogl  has  been  given,  and  which  may  be  viewed  as  the 
radical  of  the  alcohol  of  caproic  acid  C,2H,30,HO,  still  to  be  discovered. 

Castor-oil  has  lately  become  the  source  of  a  new  alcohol  in  the  hands  of 
M,  Bonis,  According  to  his  researches,  there  is  present  in  castor-oil  a  pecu- 
liar oleic  acid,  ricinoleic^  acid,  which  contains  C3gFl3gOg,HO,  i,  e,,  2  eq.  of 
oxj'gen  more  than  common  oleic  acid.  If  this  acid,  or  more  conveniently 
castor-oil  itself,  be  heated  with  solid  hydrate  of  potassa,  an  oily  liquid  distils 
over,  boiling  at  356°  (180°C).  which  is  the  alcohol  of  caprylic  acid.  It  con- 
tains C,8H,70,HO,  and  is  readily  converted  into  caprylic  acid  (see  page  485), 
by  treatment  with  oxidizing  agents.  The  residue  in  the  retort  contains 
sebacate  of  potassa.  This  transformation  is  represented  by  the  following 
equation : — 

C36H3505,H0  -f  2(K0,H0)  =  2KO,C2oH,606  -f  0,^^,.,0,nO  -f  2H 

Ricinoleic  acid.  Sebacate  of  potassa.  Caprylic  alcohol. 

VOLATILE    OILS. 

The  volatile  oils  of  the  vegetable  kingdom  are  exceedingly  numerous ;  they 
are  secreted  by  plants,  and  confer  upon  their  flowers,  fruits,  leaves,  and 


VOLATILE    OILS.  489 

wood  their  peculiar  odours.  These  substances  are  mostly  procured  by  dis- 
tilling the  plant,  or  part  of  the  plant,  with  water ;  their  points  of  ebullition 
always  lie  above  that  of  water;  nevertheless,  at  212°  (100°C)  the  oils  emit 
vapour  of  very  considerable  tension,  which  is  carried  over  mechanically,  and 
condensed  with  the  steam.  The  milky,  or  turbid  liquid  obtained,  when  left 
at  rest,  separates  into  oil  and  water.  Sometimes  the  oil  is  heavier  than  the 
water,  and  sinks  to  the  bottom ;  sometimes  the  reverse  happens. 

The  volatile  oils,  when  pure,  are  colourless ;  they  very  frequently,  how- 
ever, have  a  yellow,  and  in  rarer  cases,  a  green  colour,  from  the  presence 
of  impurity.  The  odour  of  these  substances  is  usually  powerful,  and  their 
taste  pungent  and  burning.  They  resist  saponification  completely,  but  when 
exposed  to  the  air  frequently  become  altered  by  slow  absorption  of  oxygen, 
and  assume  the  character  of  resins.  They  mix  in  all  proportions  with  fat 
oils,  and  dissolve  freely  both  in  ether  and  alcohol ;  from  the  latter  solvent 
they  are  precipitated  by  the  addition  of  water.  As  already  mentioned,  the 
volatile  oils  communicate  a  gi-easy  stain  to  paper,  which  disappears  by  warm- 
ing ;  by  this  character  any  adulteration  with  fixed  oils  can  be  at  once  de- 
tected. A  solid,  crystalline  matter,  corresponding  to  the  margarine  of  the 
common  oils,  frequently  separates  from  these  bodies ;  it  bears  the  general 
name  of  stearoptene,  and  differs  probably  in  almost  every  case. 

The  essential  oils  may  be  conveniently  divided  into  three  classes;  viz., 
those  consisting  of  carbon  and  hydrogen  only  ;  those  consisting  of  carbon, 
hydrogen,  and  oxygen ;  and  those  containing  in  addition  sulphur  and  nitrogen. 

Oils  composed  of  Carbon  and  Hydrogen. 

Oil,  or  essence  of  turpentin. — This  substance  may  be  taken  as  the  type 
or  representative  of  the  class  ;  it  is  obtained  by  distilling  with  water  the  soft 
or  semi-fluid  balsam  called  in  commerce  crude  turpentine,  which  exudes  from 
various  pines  and  firs,  or  flows  from  wounds  made  for  the  purpose  in  the 
wood.  The  solid  product  left  after  distillation  is  common  resin.  Oil  of  tur- 
pentin,  when  farther  purified  by  rectification,  is  a  thin,  colourless  liquid, 
of  powerful  and  well-known  odour:  its  density  in  the  liquid  state  is  0-865, 
and  that  of  its  vapour  4-764;  it  boils  at  312°  (155o-5C).  In  water  it  dis- 
solves to  a  small  extent,  and  in  strong  alcohol  and  ether  much  more  freely ; 
with  fixed  oils  it  mixes  in  all  proportions.  Strong  sulphuric  acid  chars  and 
blackens  this  substance  ;  concentrated  nitric  acid  and  chlorine  attack  it  with 
such  violence  that  inflammation  sometimes  ensues. 

Oil  of  turpentin  is  composed  of  C5II4  or  G^o^i^. 

With  hydrochloric  acid  the  oil  forms  a  curious  compound,  which  has  been 
called  artificial  camphor  from  its  resemblance  in  odour  and  appearance  to  that 
substance.  It  is  prepared  by  passing  dry  hydrochloric  acid  gas  into  the 
pure  oil,  cooled  by  a  freezing  mixture.  After  some  time,  a  white,  crys- 
talline substance  separates,  which  may  be  strained  from  the  supernatant 
brown  and  highly  acid  liquid,  and  purified  by  alcohol,  in  which  it  dissolves 
very  freely.  This  substance  is  neutral  to  test-paper,  does  not  affect  nitrate 
of  silver,  and  sublimes  without  much  decomposition  ;  it  contains  Q^^^,C\, 
or  perhaps  CjoHig.HCl.  The  dark  mother-liquid  contains  a  somewhat  similar, 
but  fluid  compound.  Different  specimens  of  oil  of  turpentin  yield  very 
vrtriable  quantities  of  these  substances,  which  may,  perhaps,  arise  from  the 
co-existence  of  trvo  very  similar  and  isomeric  oils  in  the  ordinary  ai'ticle. 
When  these  hydrochlorates  are  decomposed  by  distillation  with  lime,  they 
yield  liquid  oily  products  differing  in. some  particulars  from  the  original  oil 
of  turpentin,  but  have  the  same  composition  as  that  substance.  That  from 
the  solid  has  received  the  name  of  caviphylene,  and  that  from  the  liquid  conk^ 
pound  lerehylene.     The  hypothetical  and  non-isolable  modifications  of  the  oil 


490  VOLATILE    OILS. 

supposed  to  exist  in  the  solid  comphor  are  termed  respectively  camphene  and" 
terebene. 

Anothef  isomeric  compound,  colophene,  is  produced  by  distilling  oil  of  tur- 
pentin  with  coucentrated  sulphuric  acid.  It  is  a  viscid,  oily,  colourless 
liquid,  of  high  boiling-point,  and  exhibiting  by  reflected  light  a  deep  bluish 
tint, — a  phenomenon  often  remarked  in  bodies  of  this  class. 

Bromine  and  iodine  also  form  compounds  -with  oil  of  turpentin. 

Oil  of  turpentin  is  very  largely  used  in  the  arts,  in  painting,  and  as  a  sol- 
vent for  resins  in  making  varnishes. 

Bottles  in  v^hich  rectified  oil  of  turpentin,  not  purposely  rendered  anhy- 
drous, has  been  preserved,  are  often  studded  in  the  interior  with  groups  of 
beautiful,  colourless,  prismatic  crystals,  which  form  spontaneously.  These 
have  the  composition  of  a  hydrate  of  oil  of  turpentin.    These  crystals  contain 

Oil  of  lemons  is  expressed  from  the  rind  of  the  fruit,  or  obtained  by  dis- 
tillation with  water.  This  oil  differs  very  much  from  the  last  in  odour,  but 
closely  resembles  it  in  other  respects.  It  has  the  same  composition  as  oil 
of  turpentin,  and  forms  with  hydrochloric  acid  two  compounds ;  one  solid 
and  crystalline,  the  other  fluid.     The  solid  contains  Ci„HgHCl. 

The  oils  of  orange-peel,  bergamot,  pepper,  cubebs,  Juniper,  capivi,  elemi,  the 
laurel-oil  of  Guiana,  the  East  Indian  grass-oil,  and  the  principal  part  of  hop- 
oil,  are  hydrocarbons,  isomeric  with  the  oils  of  turpentin  and  lemons. 

Essential  Oils  containing  Oxygen. 

The  essential  oils  containing  oxygen  are  very  numei-ous,  and  in  fact  make 
up  the  great  bulk  of  the  bodies  of  this  class  employed  in  medicine  and  per- 
fumery. They  are  seldom  homogeneous,  and  in  consequence  do  not  often 
exhibit  fixed  boiling-points.  Some  of  these  oils  have  been  made  the  subjects 
of  much  chemical  research,  but  the  majority  yet  require  examination.  Tl-ree 
of  the  most  interesting,  viz.,  those  of  bitter  almonds,  cinnamon,  and  the 
Spircea  ulmaria  have  been  already  described. 

Oil  of  aniseed. — The  oil  distilled  from  the  seeds  of  the  Pimpinella  anisum 
consists  of  two  substances,  one  of  which  is  a  fluid  oil,  and  the  other  a  solid 
crystalline  substance,  so  abundant  as  to  cause  the  whole  to  solidify  at  a  tem- 
perature of  60°  (10°C).  By  pressure  between  folds  of  bibulous  paper  and 
crystallization  from  alcohol,  the  solid  essence  may  be  obtained  pure.  It 
forms  colourless  pearly  plates,  more  fragrant  in  odour  than  the  crude  oil, 
which  melt  when  gently  heated,  and  distil  at  a  high  temperature.  It  con- 
tains CjoHijOa-  This  substance  is  attacked  energetically  by  chlorine,  bro- 
mine, and  nitric  acid ;  it  combines  with  hydrochloric  acid,  but  is  unaffected 
by  solution  of  caustic  potassa.  With  bromine  the  solid  essence  yields  a 
white  inodorous  crystallizable  compound,  bromanisal,  containing  C2o(HgBr3)Og. 
The  action  of  chlorine  is  more  complex,  several  successive  compounds  being 
produced.  With  sulphuric  acid  two  products  are  obtained,  a  compound  acid 
analogous  to  sulphovinic  acid,  and  a  white,  solid  neutral  substance,  anisoin, 
isomeric  with  the  essence. 

The  products  of  the  action  of  nitric  acid  vary  with  the  strength  of  the 
acid  employed ;  the  most  important  are  hydride  of  anisyl ;  anisic  acid,  a  sub- 
■stance  very  much  resembling  salicylic  acid  in  properties,  sparingly  soluble 
in  cold  water,  freely  in  alcohol  and  ether ;  nitranisic  acid,  a  yellowish- white, 
crystalline  sparingly-soluble  powder ;  and  nitraniside,  a  resinous  body  pro- 
duced by  fuming  nitric  acid. 

The  hydride  of  anisyl  in  a  pure  state  is  a  yellowish  oily  liquid,  having  an 
uromatic  odour  of  hay ;  it  is  heavier  than  water,  and  boils  at  400°  (254°-oC). 
Caustic  potassa,  concentrated  and  boiling,  slowly  decomposes  it;  with  fused 


VOLATILE    OILS.  491 

hydrate  of  potassa,  it  is  instantly  converted  into  anisic  acid  with  disengage 
ment  of  hydrogen ;  air  and  oxidizing  bodies  in  general  produce  the  same 
effect.  Ammonia  forms  with  it  a  crystalline  compound  analogous  to  hydro- 
benzaraide.     Hydride  of  anisyl  contains  CigHgO^. 

Anisic  acid  contains  €,611705, HO,  i.  e.,  hydride  of  anisyl  and  2  eq.  of 
oxygen.  When  treated  with  an  excess  of  lime  or  baryta,  it  suffers  a  decom 
position,  analogous  to  that  of  benzoic  and  salicylic  acid,  losing  2  eq.  of  car- 
bonic acid,  and  being  converted  into  an  oxygenated  oil,  boiling  at  302" 
(150°C),  to  which  the  name  anisol  has  been  given. 

C,6H70„HO+2CaO=2(CaO,C02)  +  C,4HgOa 

Anisic  acid.  Anisol. 

Nitranisic  acid  is  the  nitro-substitute  of  anisic  acid;  it  contains  Cie(H, 
N04)05,HO. 

The  solid  portion  of  the  oils  of  bitter  fennel  and  badian  is  identical  with 
that  of  oil  of  aniseed.  The  fluid  component  of  the  fennel-oil  is  isomeria 
with  oil  of  turpentin. 

Draconic  acid,  obtained  by  the  action  of  nitric  acid  upon  the  oil  of  Arte' 
misia  dracunculus,  is  identical  with  anisic  acid. 

The  various  substances  belonging  to  this  group  are  homologous  to  thi 
members  of  the  salicyl-series,  described  in  a  former  part  of  the  Manual 
(see  page  404),  as  may  be  seen  from  the  following  comparison : — 

Hydride  of  salicyl 0,4     Hg       O4;  C,g     Hg       O4  Hydride  of  anisyl. 

Salicylic  acid  C14     Hg       Og;C,g     Hg       Og  Anisic  acid. 

""■"dr::?!:'.!.!!!."!!!....  }  ^u  {  \  }  O,  ■,  C,  {  \ ]  O.  Nitra„isi.  acid. 
^''n7)\!!'.!.'!?!!.°'.y:^!:}c..    «>      0,;C„    H,       CArnsol. 

Oil  of  cumin  is  a  mixture  of  two  bodies,  separable  in  great  measure  by 
distillation,  cr/mol,  a  liquid  hydrocarbon,  containing  C2oH,4,  the  most  volatile 
portion  of  the  oil,  and  cuminol,  a  colourless  transparent  oil,  of  powerful  odour, 
easily  changed  in  the  air,  and  only  to  be  distilled  in  a  current  of  carbonic  acid 
gas.  Cuminol  contains  CgoHijOg,  and  is  consequently  isomeric  with  the  solid 
essence  of  aniseed.  By  oxidation,  this  substance,  which  is  homologous  to  oil 
of  bitter  almonds,  yields  cumicacid,  a  white,  fatty,  volatile  substance,  insolu- 
ble in  water,  having  but  little  odour,  and  crystallizing  in  prismatic  tables. 
It  contains  CgoHijOg.HO  (see  homologues  of  benzoic  acid,  page  403). 

Oil  of  cedar-wood,  in  like  manner,  contains  two  substances,  a  solid  crys- 
talline compound,  having  the  formula  C32H2g02,  and  a  volatile  liquid  hydro- 
carbon, cedrene,  C32H24,  which  can  also  be  obtained  by  distilling  the  solid 
with  anhydrous  phosphoric  acid. 

Oil  of  gaultheria  procumbens. — This  very  remartable  substance  is  now 
known  in  commerce  under  the  name  of  winter-green-oil ;  it  consists  almost 
wholly  of  a  definite  principle  which  distils  unchanged  at  435°  (223° -80),  and 
contains,  according  to  the  analysis  of  M.  Cahours,  CigHgOg.  When  mixed  with 
dilute  caustic  potassa,  it  solidifies  to  a  crystalline  mass,  which  is  a  potassa- 
salt,  gaultherate  of  potassa,  and  from  which  the  oil  may  be  separated  again 
unchanged  on  the  addition  of  an  acid.  When  distilled,  however,  with  a  con- 
centrated solution  of  caustic  potassa,  the  oil  of  gaultheria  is  resolved  into 
salicylic  acid  and  wood-spirit,  thus  exactly  resembling  in  its  behaviour  the 
compound  ethers  which  have  been  described  in  a  previous  section  of  the 
Manual  (see  page  352).  This  oil  is,  in  fact,  a  veritable  compound  ether, 
salicylate  of  oxyde  of  methyl,  C2N30,Ci4H505=:C,gng06,  furnished  by  nature 
herself.  With  ammonia  the  oil  jHields  salicylamide,  C,4n7N04=C,4Hg04,NH2, 
isomeric  with  anthranilic  acid  (see  page  474),  which  is  converted  by  fuming 


492  VOLA.TILE    OILS. 

nitric  acid  into  the  nitro-substitute,  nitro-salicylamide  (anilamide)  Cj^CH^ 
N04.)()^,NH2,  crj'stalliziug  in  yellowish-white  needles.  Gaultheria  oil  is  iso- 
meric with  anisic  acid  (see  page  491),  and  yields  by  distillation  at  a  high  tem- 
perature with  anhydrous  lime  and  baryta,  anisol  C,4Hg05,  the  same  volatile 
oily  liquid  which  is  obtained  from  anisic  acid  by  a  similar  process. 

Oil  of  valerian. — The  oil  obtained  by  distilling  valerian-root  with  water 
has  usually  a  viscid  consistence,  a  yellowish  colour,  and  a  powerful  and  dis- 
agreeable odour.  It  consists  of  at  least  three  principles,  namely,  valeric  acid, 
borneene  (see  camphor),  a  light  volatile  liquid  hydrocarbon,  much  resembling 
and  isomeric  with  oil  of  turpentin,  and  valerol,  a  neutral  oily  body,  much 
less  volatile  than  the  preceding,  of  feeble  odour,  and  convertible  by  oxidizing 
agents  into  valeric  acid.  It  contains  Cj^Hj^O^.  Borneene,  under  certain 
circumstances  not  well  understood,  assimilates  the  elements  of  water  and 
yields  the  solid  camphor  of  Borneo,  or  horneol. 

Camphob. — Common  camphor  yields  a  good  example  of  a  concrete  essen- 
tial oil ;  it  is  obtained  by  distilling  with  water  the  wood  of  the  Laurus  cam- 
phora.  When  pure,  it  forms  a  solid,  white,  crystalline,  and  translucent 
mass,  tough,  and  diflBcult  to  powder,  and  having  a  powerful  and  very  fami- 
liar odour.  It  melts  when  gently  heated,  and  boils,  distilling  unchanged  at 
a  high  temperature.  It  slowly  sublimes  at  the  temperature  of  the  air,  and 
often  forms  beautiful  crystals  on  the  sides  of  bottles  or  jars  containing  it 
exposed  to  the  light.  Camphor  is  very  sparingly  soluble  in  water,  but  readily 
soluble  in  alcohol,  ether,  and  strong  acetic  acid.     It  contains  CjoHgO,  or 

^20^16^2- 

By  the  action  of  nitric  acid  aided  by  heat,  camphor  is  gradually  oxidized 
and  dissolved  with  production  of  camphoric  acid;  this  substance  forms  small 
colourless  needles  or  plates,  of  acid  and  bitter  taste,  sparingly  soluble  in 
cold  water,  and  containing  CioH703,HO.  It  melts  when  heated,  and  yields 
by  distillation  a  colourless,  crystalline,  neutral  substance,  containing  CiqH, 
O3,  improperly  termed  anhydrous  camphoric  acid. 

When  camphorate  of  lime  is  submitted  to  distillation,  it  yields  a  volatile 
oil  containing  oxygen,  in  its  formation  and  constitution  similar  to  acetone 
(page  376)  or  benzophenone  (page  898).  This  substance,  jpAorone,  contains 
Cgtl^O  or  C, 8111402.  By  the  action  of  anhydrous  phosphoric  acid  it  loses 
water  and  furnishes  the  hydrocarbon  cumol,  CigHjj  (see  page  403). 

When  camphor  in  vapour  is  passed  over  a  mixture  of  hydrate  of  potassa 
and  quicklime  strongly  heated  in  a  tube,  it  is  resolved  without  disengage- 
ment of  gas  into  an  acid  body  termed  camphoUc  acid,  white,  crystalline,  and 
sparingly  soluble  in  water,  containing  CjoHj^OgJIO.  By  distillation  with 
anhydrous  phosphoric  acid,  this  acid  gives  a  volatile  hydrocarbon,  campko- 
lene.  Camphor  itself,  by  a  similar  mode  of  treatment,  yields  a  colourless 
volatile  liquid,  CjoH,^,  formerly  called  camphogen,  but  since  found  to  be  iden- 
tical with  the  hydrocarbon,  cymol,  occurring  in  oil  of  cumin. 

The  camphor  of  Borneo,  procured  from  the  Dryahalanops  camphora,  contains 
CgoHjgOg ;  it  is  accompanied  by  borneene,  identical  with  that  of  the  oil  of 
valerian,  and  yields  the  same  substance  when  distilled  with  anhydrous  phos- 
phoric acid.     Nitric  acid  converts  it  into  common  camphor. 

The  oils  of  peppermint,  lavender,  rosemary,  orange-flowers,  rose-petals,  and 
manv  others,  belong  to  the  class  of  oxygenated  essential  oils. 

Essential  Oils  containing  Sulphur. 

In  the  preparation  of  the  sulphuretted  volatile  oils,  distillatory  vessels  of 
copper,  tia,  or  lead  must  be  avoided,  as  those  metals  are  attacked  by  the 
Rulphur.     In  other  respects  their  manufacture  offers  no  peculiarities. 

Oil  of  mustabd. — The  most  remarkable  member  of  the  class  is  the  oil 
obtained  by  distillation  from  black  mustard-seed.     White  mustard  yields 


RESINS    AND    BALSAMS.  493 

sone.  Both  varieties  give,  by  expression,  a  bland  fat  oil.  The  volatile  oil 
doeri  not  pre-exist  in  the  seed,  but  is  formed  in  the  same  manner  as  bitter- 
almond-oil,  by  the  joint  action  of  water  and  a  peculiar  coagulable  albuminous 
matter  upon  a  substance  yet  inperfectly  known,  present  in  the  grain,  and 
termed  myronic  acid. 

The  distilled  oil,  when  pure,  is  colourless ;  it  has  a  most  powerful,  pungent 
and  suffocating  smell,  and  a  density  of  1-015.  Applied  to  the  skin,  it  pro- 
duces almost  instant  vesication.  It  boils  at  289°  (145° -80).  Water  dis- 
solves it  in  small  quantity,  and  alcohol  and  ether  very  freely.  The  oil  itself, 
at  a  high  temperature,  dissolves  both  sulphur  and  phosphorus,  and  deposits 
them  in  a  crystalline  form  on  cooling.  It  is  oxidized  with  violence  by  nitric 
acid,  and  by  aqua  regia.  Alkalis  decompose  it  by  the  aid  of  heat,  with  pro- 
duction of  ammonia,  an  alkaline  sulphide,  and  a  sulphocyanide.  The  re- 
markable compound  with  ammonia,  thiosinnamine,  has  been  already  described 
(see  page  466.) 

Mustard-oil  gives  by  analysis  CgHgNSg." 

The  oil  of  horse-radish,  and  that  obtained  from  the  roots  of  the  Alliaria 
officinalis  by  distillation  with  water,  are  identical  with  the  oil  of  black  mus- 
tard-seed. 

Oil  op  garlic.  —  The  crude  oil  procured  by  distilling  the  sliced  bulbs  with 
water  is  not  a  homogeneous  product;  by  the  action  of  metallic  potassium, 
however,  renewed  until  it  is  no  longer  tarnished,  a  small  portion  of  oxyge- 
netted  oil  which  it  contains  may  be  decomposed  and  withdrawn,  after  which 
the  sulphuretted  compound  may  be  obtained  pure  by  re-distillation.  In  this 
state  it  forms  a  colourless  liquid,  lighter  than  water,  of  high  refractive  power, 
possessing  in  a  high  degree  the  peculiar  odour  of  the  plant,  and  capable  of 
being  distilled  without  decomposition.  It  contains  CgHjS.  Garlic-oil  dis- 
solved in  alcohol,  and  mixed  with  solutions  of  platinum,  silver,  and  mercury, 
gives  rise  to  crystalline  compounds  having  the  characters  of  double  salts, 
containing  the  elements  of  the  oil  with  the  sulphur  replaced  by  oxygen  or 
chlorine. 

A  curious  and  interesting  relation  exists  between  the  oils  of  mustard  and 
garlic :  in  both  these  substances,  we  may  assume  the  existence  of  a  radical 
CgHg,  to  which  the  name  allyl  has  been  given,  when  mustard-oil  becomes  the 
sulphocyanide,  and  garlic-oil  the  sulphide  of  allyl. 

Mustard-oil  CgHjNS  =C6n5C2NS2.         Sulphocyanide  of  allyl. 
Garlic-oil      CgH^S     =061158.  Sulphide  of  allyl. 

This  relation  has  been  experimentally  established.  By  mixing  the  oil 
with  hydrate  of  soda  and  quicklime,  and  exposing  the  whole  in  an  hermeti- 
cally-sealed tube  to  a  temperature  superior  to  that  of  boiling  water,  sulpho- 
cyanide of  sodium  is  produced,  together  with  an  oily  substance  which  is  oxide 
of  allyl,  a  substance  chiefly  known  in  combination,  and  which  is  the  oxyge- 
netted  constituent  of  crude  garlic-oil.  Again,  if  mustard-oil  be  treated  in  a 
similar  manner  with  sulphide  of  potassium,  sulphocyanide  of  potassium  and 
garlic-oil  are  formed.  On  the  other  hand,  when  the  compound  of  garlic-oil 
and  chloride  of  mercury  is  gently  heated  with  sulphoc3''anide  of  potassium, 
mustard-oil,  with  all  its  characteristic  properties,  is  called  into  existence. 

The  oils  of  assafostida,  and  onions,  contain  sulphur,  and  consequently  belong 
to  the  same  series  ;  they  have  not  yet  been  thoroughly  examined. 

RESINS    AND    BALSAMS. 

Common  resin,  or  colophony,  furnishes  perhaps  the  best  example  of  the 
class.     The  origin  of  this  substance  has  been  already  described.     It  is  a 
mixture  of  two  distinct  bodies,  having  acid  properties  j  cailled  j)inic  and  sylvie 
42 


494  RESINS     AND    BALSA  IMS. 

aeids,  separable  from  each  other  by  their  difference  of  solubility  in  cold  an  J 
somewhat  dilute  alcohol,  the  former  being  by  far  the  more  soluble  of  the 
two.  Pure  sylvic  acid  crystallizes  in  small,  colourless,  rhombic  prisms,  inso- 
luble in  water,  soluble  in  hot,  strong  alcohol,  in  volatile  oils,  and  in  ethei*. 
It  melts  when  heated,  but  cannot  be  distilled  without  decomposition.  The 
properties  of  pinic  acid  are  very  similar.  Both  have  the  same  composition, 
viz.,  CgoHijOj.  A  third  resin-acid,  also  isomeric  with  the  preceding,  the 
pimaric,  has  been  found  in  the  turpentin  of  the  Pinus  maritima  of  Bordeaux. 

Lac  is  a  very  valuable  resin,  much  harder  than  colophony,  and  easily  so- 
luble in  alcohol;  three  varieties  are  known  in  commerce,  viz.,  stick-lac,  seed- 
lac,  and  shellac.  It  is  used  in  varnishes,  and  in  the  manufacture  of  hats,  and 
very  largely  in  the  preparation  of  sealing-wax,  of  which  it  forms  the  chief 
ingredient.  Crude  lac  contains  a  red  dye  which  is  partly  soluble  in  water. 
Lac  dissolves  in  considerable  quantity  in  a  hot  solution  of  borax ;  Indian  ink, 
rubbed  up  with  this  liquid,  forms  a  most  excellent  label-ink  for  the  laboratory, 
as  it  is  unaffected  by  acid  vapours,  and,  when  once  dry,  becomes  nearly  in- 
soluble in  water. 

Mastic,  Dammar-resin,  and  sandarac  are  resins  largely  used  by  the  varnish- 
maker.  Dragon's-blood  is  a  resin  of  a  deep  red  colour.  Copal  is  also  a  very 
valuable  substance ;  it  differs  from  the  other  resins,  in  being  with  difficulty 
dissolved  by  alcohol  and  essential  oils.  It  is  miscible,  however,  in  the  melted 
state  with  oils,  and  is  thus  made  into  varnish.  Amber  appears  to  be  a  fossil 
resin ;  it  is  found  accompanying  brown-coal  or  lignite. 

Caoutchouc. — This  curious,  and  now  most  useful  substance,  is  the  produce 
of  several  trees  of  tropical  countries,  which  yield  a  milky  juice,  hardened  by 
exposure  to  the  air.  In  a  pure  state,  it  is  nearly  white,  the  dark  colour  of 
commercial  caoutchouc  being  due  to  the  effects  of  smoke  and  other  impuri- 
ties. Its  physical  characters  are  well  known.  It  is  softened,  but  not  dis- 
solved by  boiling  water ;  it  is  also  insoluble  in  alcohol.  In  pure  ether, 
rectified  native  naphtha,  and  coal-oil,  it  dissolves,  and  is  left  unchanged  on 
the  evaporation  of  the  solvent.  Oil  of  turpentin  also  dissolves  it,  forming 
a  viscid,  adhesive  mass,  which  dries  very  imperfectly.  At  a  temperature  a 
little  above  the  boiling-point  of  water  caoutchouc  melts,  but  never  afterwards 
returns  to  its  former  elastic  state.  Few  chemical  agents  affect  this  substance  ; 
hence  its  great  practical  use,  in  chemical  investigations,  for  connecting  ap- 
paratus, &c.  Analysis  shows  it  to  contain  nothing  but  carbon  and  hydrogen. 

By  destructive  distillation  caoutchouc  yields  a  large  quantity  of  thin  vola- 
tile oily  liquid,  of  naphtha-like  odour,  to  which  the  name  caoutchoucin  has 
been  applied.  This  is  probably  a  mixture  of  several  hydrocarbons,  scarcely 
to  be  separated  from  each  other  by  distillation  or  otherwise.  It  dissolves 
caoutchouc  with  facility. 

A  substance  much  resembling  caoutchouc  in  certain  respects,  and  of  simi- 
lar origin,  has  lately  been  introduced  under  the  name  of  guttapercha.  It  is 
capable  of  many  useful  applications  in  the  laboratory. 

Most  of  the  resins,  when  exposed  to  destructive  distillation,  yield  liquid, 
oily  pyro-products,  usually  carbides  of  hydrogen,  which  have  been  studied 
with  partial  success.  Great  difficulties  occur  in  these  investigations  ;  the 
task  of  separating  from  each  other,  and  isolating  bodies  which  scarcely  differ 
but  in  their  boiling-points,  is  exceedingly  troublesome. 

Balsams  are  also,  as  before  hinted,  natural  mixtures  of  resins  with  volatile 
oils.  These  differ  very  greatly  in  consistence,  some  being  quite  fluid,  others 
solid  and  brittle.  By  keeping,  the  softer  kinds  often  become  hard.  Balsams 
may  be  conveniently  divided  into  two  classes,  viz.,  those  which,  like  common 
and  Venice  turpentin,  Canada  balsam,  copaiba  balsam,  &c.,  are  merely  natural 
varnishes,  or  solutions  of  resins  in  volatile  oils,  and  those  which  contain  beu- 


BESINS    AND    BALSAMS.  495 

«oic  or  cinnamic  acid  in  addition,  as  Peru  and  Tolu  balsams^  and  the  solid 
resinous  benzoin  commonly  called  gum-benzoin. 

Tolu-balsam,  by  distillation  with  water,  yields  three  products;  namely, 
benzoic  acid,  cinnamein,  and  tolene,  a  volatile  colourless  hydrocarbon,  boiling  at 
338°  (170°C),  and  containing  CjoHg.  The  balsam  freed  in  this  manner  from 
essential  oils,  exposed  to  destructive  distillation,  yields  in  succession  a  vis- 
cous liquid  which  crystallizes  in  the  receiver,  and  a  thin  liquid  heavier  than 
water  ;  carbonic  acid  and  carbonic  oxide  are  largely  evolved,  and  the  retort 
is  afterwards  found  to  contain  a  residue  of  charcoal.  The  solid  product  is 
chiefly  a  mixture  of  benzoic  and  cinnamic  acids ;  the  volatile  oil  contains  at 
least  two  substances  differing  in  their  boiling-points,  and  easily  separated, 
namely,  toluol  (benzoene),  which  has  been  mentioned  already  as  a  derivjitive 
of  toluylic  acid  (see  page  403),  and  an  oily  liquid  heavier  than  water,  of  high 
boiling-point,  and  having  the  composition  and  characters  of  benzoic  ether. 

Toluol  is  a  thin,  colourless  liquid,  insoluble  in  water,  sparingly  soluble  in 
alcohol,  more  freely  in  ether ;  it  has  the  odour  of  benzol ;  its  sp.  gr.  is  0-870, 
and  it  boils  at  226°  (107°-5C).  The  density  of  its  vapour  is  3-26,  and  its  for- 
mula C,4H^.  It  combines  with  fuming  sulphuric  acid  to  the  compound  sul- 
photuolic  acid:  with  nitric  acid  it  yields  two  products,  nilrotoluol,  C14H7NO4, 
and  biniirotoluol,  Cj4HgN208.  The  former  is  fluid,  heavier  than  water,  and 
bears  a  great  resemblance  in  odour  and  other  properties  to  nitrobenzol ;  the 
latter  is  a  solid,  fusible,  crystallizable  substance.  The  conversion  of  nitro- 
toluol  into  the  organic  base  toluidine,  has  been  already  described  (see  page 
462). 

Liquid siorax  distilled  with  water,  holding  in  solution  a  little  carbonate  of 
soda,  yields  a  small  and  variable  quantity  of  volatile  oil,  not  homogeneous, 
but  from  which,  by  careful  distillation,  a  liquid  volatile  hydrocarbon,  termed 
styrol,  can  be  extracted  in  a  state  of  purity.  It  is  thin  and  colourless,  of 
powerful  aromatic  odour,  refuses  to  solidify  when  cooled  to  0°  ( — 17°-8C), 
and  boils  at  293°  (145° -C).  Its  sp.  gr.  is  0-924;  it  is  nearly  insoluble  in 
water,  but  mixes  freely  with  alcohol  and  ether.  Styrol  contains  CjgHg,  and 
is  consequently  isomei-ic  with  benzol.  This  substance  is  also  produced  by 
the  action  of  lime  or  baryta  upon  cinnamic  acid  (see  page  408),  whence  it  is 
more  appropriately  termed  cinnamol. 

When  a  portion  of  styrol  is  hermetically  sealed  in  a  glass  tube,  and  then 
exposed  for  half  an  hour  to  a  temperature  approaching  400°  (204° -50)  by 
means  of  an  oil-bath,  it  undergoes  a  most  remarkable  change,  becoming  con- 
verted into  a  solid,  transparent,  glassy,  fusible  substance,  called  metastyrol, 
isomeric,  as  might  be  expected,  with  styrol  itself.  The  same  change  is 
slowly  produced  by  the  influence  of  sunshine.  A  portion  of  metastyrol  is 
always  formed  when  styrol  is  distilled  in  a  retort  without  water.  Metastyrol 
is  again  convertible  by  distillation  at  a  high  temperature  into  liquid  styrol. 

Certain  of  the  products  of  the  distillation  of  dragon's-blood  appear  to  be 
identical  with  these  bodies. 


496     COMPONENTS  OF  THE  ANIMAL  BODY. 


SECTION    VIII. 
COMPONENTS   OF    THE   ANIMAL   BODY. 


Albuminous  principles,  albumin.  —  The  fluid  portion  of  blood  which 
has  been  some  time  drawn  from  the  living  body,  and  the  white  of  eggs,  con- 
tain this  substance  as  their  chief  and  characteristic  ingredient.  In  the 
purest  form  in  which  albumin  has  yet  been  obtained  it  is  insoluble,  or  nearly 
80,  in  water.  If  clear  serum  of  blood,  or  white  of  egg  mixed  with  a  little 
water  and  filtered,  be  exactly  neutralized  by  acetic  acid,  and  then  largely 
diluted  with  pure  cold  water,  a  copious  flocculent  precipitate  falls,  which 
may  be  collected  on  a  filter,  and  washed.  In  this  state  it  is  nearly  colour- 
less, inodorous,  and  tasteless ;  it  dissolves  with  facility  in  water  containing 
an  exceedingly  small  quantity  of  caustic  alkali,  and  gives  a  solution  which 
has  all  the  characters  of  the  original  liquid.  When  dried  by  gentle  heat, 
it  shrinks  to  a  very  small  bulk,  and  becomes  a  translucent,  horny  mass, 
which  softens  in  water,  and  exhales  when  exposed  to  heat  the  usual  ammo- 
niacal  products  of  animal  matter,  leaving  a  bulky  coal,  very  difficult  of  com- 
bustion. When  white  of  egg  is  thinly  spread  upon  a  plate  and  exposed  to 
evaporation  in  a  warm  place,  it  dries  up  to  a  pale  yellow,  brilliant,  gum-like 
substance,  destitute  of  all  traces  of  crystalline  structure.  In  this  state  it 
may  be  preserved  unchanged  for  any  length  of  time,  the  presence  of  water 
being  in  all  cases  necessary  to  putrefactive  decomposition.  The  dried  white 
of  egg  may  also  be  exposed  to  a  heat  of  212°  (100°C)  without  alteration 
of  properties.  When  put  into  slightly  warm  water,  it  softens,  and  at  length 
in  great  measure  dissolves.  When  reduced  to  fine  powder  and  washed  upon 
a  filter  with  cold  water,  common  salt,  sulphate,  phosphate,  and  carbonate 
of  soda  are  dissolved  out,  together  with  mere  traces  of  organic  matter,  while 
a  soft  swollen  mass  remains  upon  the  filter,  which  has  all  the  characters  of 
pure  albumin  obtained  by  precipitation.  When  dried  and  incinerated,  this 
leaves  nothing  but  a  little  phosphate  of  lime. 

It  thus  appears  likely  that  albumin  is  really  an  insoluble  substance,  and 
that  its  soluble  state  in  the  animal  system  is  due  to  the  presence  of  a  little 
alkali. 

When  natural  albumin  is  exposed  to  heat  it  solidifies,  or  coagulates.  The 
temperature  required  for  this  purpose  varies  with  the  state  of  dilution.  If 
the  quantity  of  albumin  be  so  great  that  the  liquid  has  a  slimy  aspect,  a 
heat  of  145°  or  150°  (62°-5  or  69°-5C)  suffices,  and  the  whole  becomes  solid, 
white,  and  opaque ;  in  a  very  dilute  condition,  boiling  is  required,  and  the 
albumin  then  separates  in  light,  finely  divided  flocks.  Thus  changed  by 
heat,  albumin  becomes  quite  insoluble  in  water;  it  dries  up  to  a  yellow, 
transparent,  horny  substance,  which  when  macerated  in  water  resumes  its 
former  whiteness  and  opacity.  In  dilute  caustic  alkali  it  dissolves  with 
facility,  and  in  this  respect  resembles  the  insoluble  albumin  just  desci'ibed; 
it  differs,  however,  from  the  latter  in  not  being  soluble  in  a  strong  solution 


COMPONENTS  OF  THE  ANIMAL  BODY.     497 

of  nitrate  of  potassa,  -which  dissolves  with  great  ease  that  substance.  The 
or>ly  chemical  change  that  can  be  traced  in  the  act  of  coagulation  is  the  loss 
of  alkali  and  soluble  salts,  which  are  removed  by  the  hot  water. 

A  solution  of  ordinary  albumin  gives  precipitates  with  excess  of  sulphuric, 
hydrochloric,  nitric,  and  Twe'a-phosphoi'ic  acids ;  but  neither  with  acetic  nor 
with  common  or  tribasic  phosphoric  acid.  These  precipitates,  which,  though 
soluble  in  water,  are  insoluble  in  an  excess  of  dilute  acid,  are  looked  upon 
as  direct  compounds  of  albumin  with  the  acids  in  question.  Most  of  the 
metallic  salts,  as  those  of  copper,  lead,  mercury,  &c.,  form  insoluble  com 
pounds  with  albumin,  and  give  precipitates  with  its  solution ;  hence  the 
value  of  white  of  egg  as  an  antidote  in  cases  of  poisoning  with  corrosive 
sublimate.  Alcohol,  added  in  large  quantity,  precipitates  albumin.  Tannic 
acid,  or  infusion  of  galls,  gives  with  it  a  copious  precipitate.  By  these  cha- 
racters the  presence  of  albumin  may  be  readily  discovered,  and  its  identi- 
tication  effected ;  a  very  feebly  alkaline  liquid,  if  containing  albumin,  coagu- 
lates by  heat,  becomes  turbid  on  the  addition  of  nitric  acid,  and  previously 
acidulated  by  acetic  acid,  gives  a  precipitate  with  solution  of  corrosive 
sublimate.  It  must  be  remembered,  that  a  considerable  quantity  of  alkali, 
and  very  minute  quantities  of  the  mineral  acids,  prevent  coagulation  by  heat, 
and  the  addition  of  acetic  acid,  indispensable  to  the  mercury-test,  produces 
the  same  effect. 

The  chemical  composition  of  albumin  has  been  carefully  studied  ;  it  con- 
tains in  100  parts  : — 

Carbon 63'5 

Hydrogen 7-0 

Nitrogen 15-5 

Oxygen 22  0 

Phosphorus 0-4 

Sulphur 1-6 


1000 


The  existence  of  unoxidized  sulphur  in  albumin  is  easily  shown ;  a  boiled 
egg  blackens  a  silver  spoon  from  a  trace  of  alkaline  sulphide  formed  or  sepa- 
rated during  the  coagulation  ;  and  a  solution  of  albumin  in  excess  of  caustic 
potassa,  mixed  with  a  little  acetate  of  lead,  gives  on  boiling  a  black  preci- 
pitate containing  sulphide  of  lead. 

FiBKiN. — This  substance  is  found  in  solution  in  the  blood.  It  is  procured 
by  washing  the  coagulum  of  blood  in  a  cloth  until  all  the  soluble  portions 
are  removed,  or  by  agitating  fresh  blood  with  a  bundle  of  twigs,  when  the 
fibrin  attaches  itself  to  the  latter,  and  is  easily  removed  and  cleansed  by 
repeated  washing  with  cold  water.  The  only  impurity  then  remaining  is  a 
small  quantity  of  fat,  which  can  be  extracted  by  ether.  In  the  fresh  state 
tibrin  forms  long,  white,  elastic  filaments;  it  is  quite  tasteless,  and  inso- 
luble in  both  hot  and  cold  water.  By  long-continued  boiling  it  is  partly 
dissolved.  When  dried  in  vacuo,  or  at  a  gentle  heat,  it  loses  about  80  per 
cent,  of  water,  and  becomes  translucent  and  horny ;  in  this  state  it  closely 
resembles  coagulated  albumin.  Fresh  fibrin  wetted  with  concentrated  acetic 
acid,  forms,  after  some  hours,  a  transparent  jelly,  which  slowly  dissolves 
in  pure  water ;  put  into  a  very  dilute  caustic  alkali,  fibrin  dissolves  com- 
pletely, and  the  solution  exhibits  many  of  the  characters  of  albumin.  Phos- 
phoric acid  produces  a  similar  effect.  Boiled  with  strong  hydrochloric  acid 
for  several  hours,  fibrin  is  converted  into  a  mixture  of  leucine  ('see  page  477) 
and  tyrosine  (see  page  500). 

The  fibrin  of  arterial  and  venous  blood  is  not  absolutely  the  same  ;  wnen 
the  venous  fibrin  of  human  blood  is  triturated  in  a  mortar  with  1  \  times  its 
42  * 


498  COMPONENTS    OF    THE    ANIMAL    BODY. 

weight  of  water  and  J  of  its  weight  of  nitrate  of  potassa,  and  the  mixture  ia 
left  24  hours  or  more  at  a  temperature  of  100°— 120°  (37°-7— 48°-8C),  it 
becomes  gelatinous,  slimy,  and  eventually  entirely  liquid ;  in  this  condition 
it  exhibits  all  the  properties  of  a  solution  of  albumin  which  has  been  neu- 
tralized by  acetic  acid.  It  coagulates  by  heat,  it  is  precipitated  by  alcohol, 
corrosive  sublimate,  &c,,  and  when  largely  diluted  it  deposits  a  flocculent 
substance,  not  to  be  distinguished  from  insoluble  albumin,'  With  arterial 
fibrin,  on  the  contrary,  no  such  liquefaction  happens,  and  even  the  fibrin  of 
venous  blood,  when  long  exposed  to  the  air,  or  to  oxygen  gas,  loses  the  pro- 
perty in  question. 

In  the  soluble  state,  fibrin  is  in  great  measure  unknown ;  when  withdrawn 
from  the  influence  of  life,  it  coagulates  spontaneously  after  a  certain  interval, 
giving  rise  to  the  production  of  the  clot  which  appears  in  blood  left  to  itself, 
and  which  consists  of  a  kind  of  fine  net-work  of  fibres,  swollen  with  liquid 
serum,  and  inclosing  the  little  red  colouring  particles  of  the  blood,  hereafter 
to  be  described. 

Mr.  Mulder  found  dried  fibrin,  carefully  freed  from  fat,  to  be  composed  as 
follows : — 

Carbon  52-7 

Hydrogen 6-9 

Nitrogen 15-4 

Oxygen 235 

Phosphorus 0-3 

Sulphur 1-2 

100-0 

The  ash,  or  incombustible  portion  of  fibrin,  varying  from  0*7  to  2-5  per 
cent,  consists  chiefly  of  the  phosphate  of  lime. 

Casein.  — This  is  the  characteristic  azotized  component  of  milk,  and  the 
basis  of  the  various  preparations  termed  cheese ;  it  is  not  known  to  occur  in 
any  other  secretion.  Casein  very  closely  resembles  albumin  in  many  par- 
ticulars, and  may  even  be  occasionally  confounded  with  it.  Like  that  sub- 
stance, it  is  insoluble  in  water  when  in  a  state  of  purity,  and  only  assumes 
the  soluble  condition  in  the  presence  of  free  alkali,  of  which,  however,  a  very 
small  quantity  suffices  for  the  purpose.  To  prepare  casein,  fresh  milk  is 
gently  warmed  with  dilute  sulphuric  acid,  the  coagulum  produced  well  washed 
with  water,  dissolved  in  a  dilute  solution  of  carbonate  of  soda,  and  placed  in 
a  warm  situation  to  allow  the  fat  or  butter  to  separate  from  the  watery 
liquid.  The  latter  is  then  removed  by  a  siphon,  and  re-precipitated  by  sul- 
phuric acid.  These  precipitations  and  re-solutions  in  dilute  alkali  are  several 
times  repeated.  Lastly,  the  insoluble  casein  is  well  washed  with  boiling 
water,  and  treated  with  ether  to  remove  the  last  traces  of  fat.  In  this  state 
it  is  a  white  curdy  substance,  not  sensibly  soluble  in  pure  water  or  in  alcohol, 
but  dissolved  with  great  ease  by  water  containing  a  little  caustic  or  carbo- 
nated alkali.  It  is  also  soluble  to  a  certain  extent  in  dilute  acids,  from 
which  it  may  be  precipitated  by  cautious  neutralization.  The  precipitate 
formed  by  an  acid  in  a  strong  solution  of  casein  contains  acid  in  combination, 
which,  however,  may  be  entirely  removed  by  washing.  In  the  moist  state 
casein  reddens  litmus-paper,  and  masks  the  reaction  of  an  alkaline  car- 
bonate When  incinerated,  it  leaves  about  0-3  per  cent,  of  incombustible 
matter. 

A  solution  of  casein  in  very  dilute  alkali,  as  in  milk,  does  not  coagulate 
on  boiling.     On  evaporation  the  surface  becomes  covered  by  a  skin,  and  the 

'  Liebig,  llandwcirterbtich  der  Cbemie,  i.  881. 


COMPONENTS  OF  THE  ANIMAL  BODY.    499 

•whole  eventually  dries  up  to  a  translueent  mass.  Acetic  acid  precipitates 
casein,  which  is  a  distinctive  character  between  that  substance  and  albumin. 

By  fusion  with  hydrate  of  potassa  casein  yields  valerianic  and  butyric 
acids,  besides  other  products. 

The  most  striking  property  of  casein  is  its  coagulability  by  certain  animal 
membranes.  This  is  well  seen  in  the  process  of  cheese-making,  in  the  pre- 
paration of  the  curd.  A  piece  of  the  stomach  of  the  calf,  with  its  mucous 
membrane,  is  slightly  washed,  put  into  a  large  quantity  of  milk,  and  the 
whole  slowly  heated  to  about  122°  (50'^C).  In  a  short  time  after  this  tem- 
perature has  been  attained,  the  milk  is  observed  to  separate  into  a  solid, 
white  coagulum,  or  mass  of  curd,  and  into  a  yellowish,  translucent  liquid 
called  whey.  The  curd  contains  all  the  casein  of  the  milk,  much  of  the  fat, 
and  much  of  the  inorganic  matter  ;  the  whey  retains  the  milk-sugar  and  the 
soluble  salts.  It  is  just  possible  that  this  mysterious  change  may  be  really 
due  to  the  formation  of  a  little  lactic  acid  from  the  milk-sugar,  under  the 
joint  influence  of  a  slowly  decomposing  membrane  and  the  elevated  tempe- 
rature, and  that  this  acid  may  be  sufficient  in  quantity  to  withdraw  the 
alkali  which  holds  the  casein  in  solution,  and  thus  occasion  its  precipitation 
in  the  insoluble  state.  The  loss  of  weight  the  membrane  itself  suffers  in  this 
operation  is  very  small ;  it  has  been  found  not  to  exceed  y^'o^  part. 

Casein  has  been  carefully  analysed  by  Mulder ;  it  contains  in  100  parts — 

Carbon  53-83 

Hydrogen 7-15 

Nitrogen  15-65 

Oxygen  \  00.07 

Sulphur/ "^^"^^ 

100-00 

When  precipitated  by  acetic  acid  and  washed  with  alcohol  and  ether  it 
contains  about  1  per  cent,  of  sulphur.  When  not  treated  with  acid  it  con- 
tains about  6  per  cent,  of  phosphate  of  lime. 

A  comparison  of  the  composition  of  these  three  bodies  described  is  very 
remarkable,  as  it  shows  that  they  are  very  closely  related  in  composition. 
The  fibrin  contains  rather  a  larger  quantity  of  oxygen  than  the  albumin,  and 
the  casein  contains  no  phosphorus.  As,  however,  it  is  very  doubtful  whether 
these  substances  have  been  obtained  in  an  unmixed  and  pure  state  no  for- 
mulae can  be  given. 

Protein. — Mulder  observed  that  when  albumin,  fibrin,  or  casein  was  dis- 
solved in  a  moderately  strong  solution  of  caustic  alkali,  and  digested  at  140° 
((30° -C),  or  thereabouts,  in  an  open  vessel  until  the  liquid  ceased  to  blacken 
with  a  salt  of  lead,  and  then  filtered,  and  mixed  with  a  slight  excess  of 
acetic  acid,  a  copious,  snow-white  flocculent  precipitate  fell,  and  a  faint  odour 
of  sulphuretted  hydrogen  was  evolved.  The  new  substance  he  called  pro- 
tein.' He  stated  that  it  was  free  from  sulphur  and  phosphorus,  and  that  it 
was  by  the  combination  of  different  quantities  of  these  elements  with  pro- 
tein, that  albumin,  fibrin,  and  casein,  were  produced,  the  protein  pre-existing 
in  each  of  these  substances.  It  is,  however,  now  admitted,  that  neither  by 
the  above-mentioned  treatment,  nor  in  any  way,  can  a  substance  free  from 
sulphur  be  obtained,  and  the  protein  must  therefore  be  considered  as  one  of 
the  first  products  of  the  decomposition  of  albumin,  fibrin,  and  casein,  by 
moderately  strong  caustic  alkali. 

When  albumin,  fibrin,  or  casein,  are  boiled  in  strong  solution  of  potai*pa 

•  So  called  from  rpwrtt'd),  Iial:e  the  first  pUi£i;  in  allusion  to  its  alleged  important  relationo 
te  tb«  iilbumiuous  principles. 


500     COMPONENTS  OF  THE  ANIMAL  BODY. 

as  long  as  ammoniacal  vapours  are  given  off,  the  liquid  then  neutralized 
with  sulphuric  acid,  evaporated  to  dryness,  and  the  product  exhausted  by 
boiling  alcohol,  three  compounds  are  dissolved  out,  viz.,  a  soluble,  brown 
extract-like  substance,  err/throprotide  ;  a  soluble  straw-yellow  substance,  joro- 
tide,  and  a  curious  crystallizable  principle,  leucine,  which  forms  small  colour- 
less scales,  destitute  of  taste  and  odour,  soluble  in  water  and  alcohol,  and  in 
concentrated  sulphuric  acid  without  decomposition.  When  heated,  it  sub- 
limes unchanged.     Leucine  contains  CiaHjgNO^,  (see  page  501). 

Binoxide  and  Teroxide  of  Protein.  — These 'names  were  given  by  Mulder  to 
products  of  the  long-continued  action  of  boiling  water  upon  fibrin  in  contact 
with  air;  they  are  said  to  be  the  chief  ingredients  also  of  the  buffy  coat  of 
blood  in  a  state  of  inflammation,  being  produced  at  the  expense  of  the 
fibrin.'  They  cannot  be  obtained  free  from  sulphur.  Binoxide  of  protein  is 
quite  insoluble  in  water,  but  dissolves  in  dilute  acids ;  when  dry,  it  is  dark 
»;oloured.  The  soluble  part  of  the  fibrin-decoction  contains  teroxide  of  protein, 
which  somewhat  resembles,  and  has  been  confounded  with,  gelatin.  It  is 
freely  soluble  in  boiling  water,  and  in  dilute  alkalis.  Coagulated  albumin 
is  slowly  dissolved  by  boiling  water,  and  said  to  be  converted  into  this  sub- 
stance. The  solution  in  cold  water  gives  a  precipitate  with  nitric  acid  which 
is  re-dissolved  on  the  application  of  heat,  and  re-precipitated  when  cooled. 
A  substance  closely  resembling  this  in  its  reactions  and  composition  has  been 
found  in  the  urine  of  a  patient  suffering  from  molleiies  ossium.'* 

When  chlorine  gas  is  passed  to  saturation  into  a  solution  of  ordinary  albu- 
min, or  either  fibrin  or  casein  dissolved  in  ammonia,  a  white,  flocculent,  in- 
soluble substance  falls,  which,  when  washed  and  dried,  becomes  a  soft  yel- 
lowish powder.  This  is  supposed  to  be  a  compound  of  chlorous  acid  and 
protein ;  when  digested  with  ammonia,  it  yields  sal-ammoniac  and  teroxide 
of  protein. 

Gelatin  and  chondrin. — Animal  membranes,  skin,  tendons,  and  even 
bones,  dissolve  in  water  at  a  high  temperature  more  or  less  completely,  but 
with  very  different  degrees  of  facility,  giving  solutions  which  on  cooling  ac- 
quire a  soft-solid,  tremulous  consistence.  The  substance  so  procured  is 
termed  gelatin ;  it  does  not  pre-exist  in  the  animal  system,  but  is  generated 
from  the  membranous  tissue  by  the  action  of  hot  water.  The  jelly  of  calves' 
feet,  and  common  size  and  glue,  are  familiar  examples  of  gelatin  in  different 
conditions  of  purity.  Isinglass,  the  dried  swimming-bladder  of  the  stur- 
geon, dissolves  in  water  merely  warm,  and  yields  a  beautifully  pure  gelatin. 
Jn  this  state  it  is  white  and  opalescent,  or  translucent,  quite  insipid  and  in- 
odorous, insoluble  in  cold  water,  but  readily  dissolving  by  a  slight  elevation 
of  temperature.  Cut  into  slices  and  exposed  to  a  current  of  dry  air,  it 
shrinks  prodigiously  in  volume,  and  becomes  a  transparent,  glassy,  brittle 
mass,  which  is  soluble  in  warm  water,  but  insoluble  in  alcohol  and  ether. 
Exposed  to  destructive  distillation,  it  gives  a  large  quantity  of  ammonia,  in- 
flammable gases,  nauseous  empyreumatic  oil,  and  leaves  a  bulky  charcoal 
containing  nitrogen.  In  a  dry  state,  gelatin  maybe  kept  indefinitely;  in 
contact  with  water,  it  putrefies.  Long-continued  boiling  gradually  alters  it, 
and  the  solution  loses  the  power  of  forming  a  jelly  on  cooling.  1  part  of 
dry  gelatin  or  isinglass  dissolved  in  100  parts  of  water  solidifies  on  cooling. 

An  aqueous  solution  of  gelatin  is  precipitated  by  alcohol,  which  withdraws 
the  water ;  corrosive  sublimate  in  excess  gives  a  white  flocculent  precipitate, 
and  the  same  happens  with  solution  of  nitrate  of  the  sub-  and  protoxide  of 
mercury  ;  neither  alum,  acetate,  nor  basic  acetate  of  lead  affect  a  solution 
of  gelatin.     With  tannic  acid  or  infusion  of  galls,  gelatin  gives  a  copious, 

>■  Mr.ldpr,  Annalen  der  Chemie  und  Pharmade,  xlvii.  323. 
»  Se«  Philosophical  Trans.  1818. 


COMPONENTS    OP    THE   ANIxMAL    BODY.  601 

whitish,  curdy  precipitate,  which  coheres  on  stirring  to  an  elastic  mass, 
quite  insoluble  in  water,  and  incapable  of  putrefaction. 

Chlorine  passed  into  a  solution  of  gelatin  occasions  a  dense  white  precipi- 
tate of  chlorite  of  gelatin,  which  envelopes  each  gas-bubble,  and  ultimately 
forms  a  tough,  elastic,  pearly  mass,  somewhat  resembling  fibrin.  Boiling 
with  strong  alkalis  converts  gelatin,  with  evolution  of  ammonia,  into  leucine, 
and  a  sweet  crystallizable  principle,  gelatin-sugar,  or  glycocoll,  or  better, 
glycocine  containing  C4HgN04.  This  remarkable  substance  was  first  formed 
by  the  action  of  cold  concentrated  sulphuric  acid  upon  gelatin,  and  has 
lately  been  obtained  by  the  action  of  acids  upon  hippuric  acid,  which  i3 
thereby  resolved  into  benzoic  acid  and  glycocine  (see  page  402).  It  forms 
colourless  crystals,  freely  soluble  in  water,  and  unites  to  crystallizable  com- 
pounds with  a  great  number  of  bodies,  acids,  bases  and  salts.  Glycocine, 
when  treated  with  nitrous  acid,  yields  an  acid  homologous  to  lactic  acid  (see 
page  402),  to  which  the  name  of  glycolic  acid  has  been  given. 

C4H5NO4  +  NO3    =    C4H4O6  +  2N+H0 

Glycocine.  Glycolic  acid. 

This  substance,  which  is  but  imperfectly  studied,  appears  to  be  present  like 
wise  in  the  mother-liquor  from  which  the  fulminate  of  silver  has  been 
deposited.  There  exists  a  remarkable  relation  between  glycociue,  alanine, 
and  leucine,  two  substances  which  have  been  previously  described  (pages 
467  and  500).  These  three  bodies  are  homologous,  as  will  be  seen  from  the 
following  formulae  : — 

Glycocine C4H5NO4 

Alanine C6H7NO4 

Leucine Ci2H,3N04. 

The  deportments  of  these  three  substances  with  nitrous  acid  is  perfectly 
alike.  Leucine,  according  to  M.  Strecker,  yields  a  new  acid  CjjHjaOg  homo- 
logous to  glycolic  and  lactic  acids,  which  has  not  yet  been  perfectly  ex- 
amined* 

When  a  dilute  solution  of  gelatin  is  distilled  with  a  mixture  of  bichromate 
of  potassa  and  sulphuric  acid,  it  yields  a  number  of  extraordinary  products, 
as  acetic,  valerianic,  benzoic,  and  hydrocyanic  acids,  and  two  volatile  oily 
principles  termed  valeronitrile  and  valeracetonitrile.  The  former  is  a  thin 
colourless  liquid,  of  aromatic  odour,  like  that  of  hydride  of  salicyl ;  it  is 
lighter  than  water,  boils  at  257°  (125oC),  and  contains  CjoHgN.  The  latter 
much  resembles  the  first,  but  boils  at  158°  (70°C),  and  contains  C2eH24N206. 
Alkalis  convert  valeronitrile  into  valerianic  acid  and  ammonia,  and  valera- 
cetonitrile into  valerianic  and  acetic  acids  and  ammonia.  It  is  very  pro- 
bable that  the  latter  compound  is  a  mixture  of  acetonitrile  and  valeronitrile. 
Dry  gelatin,  subjected  to  analysis,  has  been  found  to  contain  in  100 
parts : — 

Carbon 5005 

Hydrogen 6  47 

Nitrogen 18-35 

Oxygen 2513 


100-00 


From  these  numbers  the  formulae  CigHioNjOg,  and  CgaH^oNgOzo,  have  been 
deduced. 

The  cartilage  of  the  ribs  and  joints  yields  a  gelatin  differing  in  some  re- 
spects from  the  preceding;  it  is  called,  by  way  of  distinction,  chondrin. 


502  COMPONENTS    OF    THE   ANIMAL   BODY. 

Acetate  of  lead  and  solution  of  alum  precipitate  this  substance,  -which  is 
not  the  case  with  common  gelatin.  To  chondrin  the  formulas  CgaH^eN^Oj^, 
and  C^gH^oNgOao  have  been  given. 

If  a  solution  of  gelatin,  albumin,  fibrin,  casein,  or  probably  any  one  of 
the  more  complex  azotized  animal  principles,  be  mixed  with  solution  of  sul- 
phate of  copper,  and  then  a  large  excess  of  caustic  potassa  added,  the 
greenish  precipitate  first  formed  is  re-dissolved,  and  the  liquid  acquires  a 
purple  tint  of  indescribable  magnificence  and  great  intensity. 

Gelatin  is  largely  employed  as  an  article  of  food,  as  in  soups,  &c, ;  but  its 
Talue  in  this  respect  has  been  much  overrated.  In  the  useful  arts,  size  and 
glue  are  consumed  in  great  quantities.  These  are  prepared  from  the  clip- 
pings of  hides,  and  other  similar  matters,  inclosed  in  a  net,  and  boiled  with 
water  in  a  large  cauldron.  The  strained  solution  gelatinizes  on  cooling,  and 
constitutes  size.  Glue  is  the  same  substance  in  a  state  of  desiccation,  the 
size  being  cut  into  slices  and  placed  upon  nettings,  freely  exposed  to  a  cur- 
rent of  air.  Gelatin  is  extracted  from  bones  with  much  greater  difficulty , 
the  best  method  of  proceeding  is  said  to  be  to  inclose  the  bones,  previously 
crushed,  in  strong  metallic  cylinders,  and  admit  high-pressure  steam,  which 
attacks  and  dissolves  the  animal  matter  much  more  easily  than  boiling 
water  ;  or,  to  steep  the  bones  in  dilute  hydrochloric  acid,  thereby  removing 
the  earthy  phosphate,  and  then  dissolve  the  soft  and  flexible  residue  by 
boiling. 

There  is  an  important  economical  application  of  gelatin,  or  rather  of  the 
material  which  produces  it,  which  deserves  notice,  viz.,  to  the  clarifying  of 
wines  and  beer  from  the  finely  divided  and  suspended  matter  which  often 
renders  these  liquors  muddy  and  unsightly.  When  isinglass  is  digested  in 
very  dilute  cold  acetic  acid,  as  sour  wine  or  beer,  it  softens,  swells,  and 
assumes  the  aspect  of  a  very  light  transparent  jelly,  which,  although  quite 
insoluble  in  the  cold,  may  be  readily  mixed  with  a  large  quantity  of  watery 
liquid.  Such  a  preparation,  technically  called  finings,  is  sometimes  used  by 
brewers  and  wine-merchants  for  the  purpose  before-mentioned ;  its  action  on 
the  liquor  with  which  it  is  mixed  seems  to  be  purely  mechanical,  the  gela- 
tinouij  matter  slowly  subsiding  to  the  bottom  of  the  cask,  and  carrying  with 
it  the  insoluble  substance  to  which  the  turbidity  was  due. 

Kreatin  and  kreatinine.  —  Kreatin  was  first  observed  by  Chevreul,  and 
has  lately  been  studied  very  carefully  by  Professor  Liebig,  who  obtained  it 
from  the  soup  of  boiled  meat ;  it  is  best  prepared  from  the  juice  of  raw  flesh 
by  the  following  process :  —  A  large  quantity  of  lean  flesh  is  cut  up  into 
shreds,  exhausted  by  successive  portions  of  cold  water,  strained  and  pressed. 
The  liquid,  which  has  an  acid  reaction,  is  heated  to  coagulate  albumin  and 
colouring  matter  of  blood,  and  passed  through  a  cloth.  It  is  then  mixed 
with  pure  baryta-water  as  long  as  a  precipitate  appears,  filtered  from  the 
deposit  of  phosphates,  and  evaporated  in  a  water-bath  to  a  syrupy  state. 
After  standing  some  days  in  a  warm  situation,  the  kreatin  is  gradually 
deposited  in  crystals,  which  are  easily  purified  by  re-solution  in  water  and 
digestion  with  a  little  animal  charcoal. 

When  pure,  kreatin  forms  colourless,  brilliant,  prismatic  crystals,  which 
become  dull  by  loss  of  water  at  212°  (100°C).  They  dissolve  readily  in  boil- 
ing water,  sparingly  in  cold,  and  are  but  little  soluble  in  alcohol.  The 
aqueous  solution  has  a  weak  bitter  taste,  followed  by  a  somewhat  acrid  sen- 
sation. In  an  impure  state  the  solution  readily  putrifies.  Kreatin  is  a  neu- 
tral body,  not  combining  either  with  acids  or  alkalis.  In  the  crystallized 
state  it  contains  C8HgN304,2HO. 

By  the  action  of  strong  acids,  kreatin  is  converted  into  kreatinine,  a  power- 
ful organic  base,  with  separation  of  the  elements  of  water.  The  new  sub- 
•tence  forms  colourless  prismatic  crystals,  and  is  much  more  soluble  in  water 


COMPOSITION     or    THE    BLOOD.  503 

than  kreatin ;  it  has  a  strong  alkaline  reaction,  forms  with  acids  crystalli- 
zable  salts,  and  contains  CgH^NgOj. 

Kreatinine  pre-exists  to  a  small  extent  in  the  juice  of  flesh,  together  with 
lactic  acid  and  other  bodies  yet  imperfectly  examined.  It  is  also  found  in 
conjunction  with  kreatin  in  urine. 

When  kreatin  is  long  boiled  with  solution  of  caustic  baryta,  it  is  gradually 
resolved  into  urea,  subsequently  decomposed  into  carbonic  acid  and  ammo- 
nia, and  a  new  organic  body  of  basic  properties,  sarcosine.  The  latter,  when 
pure,  forms  colourless  transparent  plates,  extremely  soluble  in  water, 
sparingly  soluble  in  alcohol,  and  insoluble  in  ether.  When  gently  heated 
they  melt  and  sublime  without  residue.  Sarcosine  forms  with  sulphuric  acid 
a  crystallizable  salt,  and  contains  C6H7NO4,  being  isomeric  with  lactamide, 
alanine,  and  urethane. 

The  mother-liquid  from  flesh  from  which  the  kreatine  has  been  deposited 
contains,  among  other  things,  a  new  acid,  the  inosinic,  the  aqueous  solution 
of  which  refuses  to  crystallize.  It  has  a  strong  acid  reaction,  and  is  preci- 
pitated in  a  white  amorphous  condition  by  alcohol.  It  probably  contains 
Cio^^6^2^io'HO.'  Recently,  moreover,  a  kind  of  sugar,  which  however  does 
not  ferment,  has  been  found  in  the  juice  of  flesh.  It  was  discovered  by 
Scherer,  who  calls  it  inosite,  and  gives  the  composition  Cj2Hj20j2-J-4HO, 
This  substance  crystallizes  in  beautiful  crystals. 

Composition  of  the  blood  ;  respiration. — The  blood  is  the  general  cir- 
culating fluid  of  the  animal  body,  the  source  of  all  nutriment  and  growth, 
and  the  general  material  from  which  all  the  secretions,  however  much  they 
may  differ  in  properties  and  composition,  are  derived.  Food  or  nourish- 
ment from  without  can  only  be  made  available  by  being  first  converted  into 
blood.  It  serves  also  the  scarcely  less  important  office  of  removing  and 
carrying  off  principles  from  the  body  which  are  hurtful,  or  no  longer  re- 
quired. 

In  all  vertebrated  animals  the  blood  has  a  red  colour,  and  probably  in  all 
cases  a  temperature  above  that  of  the  medium  in  which  the  creature  lives. 
In  the  mammalia  this  is  very  apparent,  and  in  the  birds  still  moi-e  so.  The 
heat  of  the  blood  is  directly  connected  with  the  degree  of  activity  of  the 
respiratory  process.  In  man  the  temperature  of  the  blood  seldom  varies 
much  from  98°  (36° -60),  when  in  a  state  of  health,  even  under  great  vicissi- 
tudes of  climate;  in  birds  it  is  sometimes  as  high  as  109°  (42°-8C).  To 
these  two  highest  classes  of  the  animal  kingdom,  the  mammifers  and  the 
birds,  the  observations  about  to  be  made  are  intended  especially  to  apply. 

In  every  creature  of  this  description  two  kinds  of  blood  are  met  with, 
which  difi'er  very  considerably  in  their  appearance,  viz.,  that  contained  in 
the  left  side  of  the  heart  and  in  the  arteries  generally,  and  that  contained 
in  the  right  side  of  the  heart  and  in  the  veins :  the  former,  or  arterial  blood, 
has  a  bright  red  colour,  the  latter,  the  venous  blood,  is  blackish  purple. 
Farther,  the  conversion  of  the  dark  into  the  florid  blood  may  be  traced  to 
what  takes  place  during  its  exposure  to  the  air  in  the  lungs,  and  the  oppo- 
site change,  to  what  takes  place  in  the  capillaries  of  the  general  vascular 
system,  or  the  minute  tubes  or  passages,  distributed  in  countless  numbers 
throughout  the  whole  body,  which  connect  the  extremities  of  the  arteries 
and  veins.  When  compared  together,  little  difference  of  properties  or  com- 
position can  be  found  in  the  two  kinds  of  blood ;  the  fibrin  varies  a  little, 
that  from  venous  blood  being,  as  already  mentioned,  soluble  in  a  solution  of 
nitrate  of  potassa,  which  is  not  the  case  with  arterial  fibrin.  It  is  very 
prone,  besides,  to  absorb  oxygen,  and  to  become  in  all  probability  partly 
changed  to  the  substance  called  binoxide  of  protein,  which  no  doubt  exists 

*  Liebig,  Chemistry  of  Food. 


504  COMPOSITION    OF    THE    BLOOD/ 

in  the  fibtin  of  arterial  blood.  The  only  other  notable  point  of  diflference  is 
in  the  gaseous  matter  the  blood  holds  in  solution,  carbonic  acid  predomina- 
ting in  the  venous,  and  free  oxygen  in  the  arterial  variety. 

In  its  ordinary  state  the  blood  has  a  slimy  feel,  a  density  varying  from 
1-053  to  1-057,  and  a  decidedly  alkaline  reaction  ; 'it  has  a  saline  and  disa- 
greeable taste,  and,  when  quite  recent,  a  peculiar  odour  or  halitus,  which 
almost  immediately  disappears.  An  odour  may,  however,  afterwards  be  de- 
veloped by  an  addition  of  sulphuric  acid,  which  is  by  some  considered  char- 
acteristic of  the  animal  from  which  the  blood  was  obtained. 

The  coagulation  of  blood  in  repose  has  been  already  noticed,  and  its  cause 
traced  to  the  spontaneous  solidification  of  the  fibrin :  the  eflfect  is  best  seen 
when  the  blood  is  received  into  a  shallow  vessel,  and  left  to  itself  some  time. 
No  evolution  of  gas  or  absorption  of  oxygen  takes  place  in  this  process.  By 
strong  agitation  coagulation  may  be  prevented ;  the  fibi'in  in  this  case  sepa- 
rates in  cohering  filaments. 

To  the  naked  eye  the  blood  appears  a  homogeneous  fluid,  but  it  is  not  so  in 
reality.    When  examined  by  a  good  microscope,  it 
^^"-  ^'^'**  is  seen  to  consist  of  a  transparent  and   nearly 

©  colourless  liquid,  in  which  float  about  a  countless 

^^  O  multitude  of  little  round  red  bodies,  to  which  the 

©  ©  ©  (^  colour  is  due ;  these  are  the  blood-discs  or  blood- 

^^  corpuscles    of  microscopic    observers.      Fig.   174. 

(^  Q  They  are  accompanied  by  colourless  globules, 
fewer  and  larger,  the  white  corpuscles  of  the  blood. 
The  blood-discs  are  found  to  present  difterent 
appearances  in  the  blood  of  difi'erent  animals:  in 
the  mammifers  they  look  like  round  red  or  yel- 
lowish discs,  thin  when  compared  with  their  diam- 
eter, being  flattened  or  depressed  on  opposite 
sides.  In  birds,  lizards,  frogs,  and  fish,  the  coi*- 
®  ©    <S)  puscles  are  elliptical.     In  magnitude,  they  seem 

©     ©  to  be  pretty  constant  in  all  the  members  of  a  spe- 

cies, but  difi'er  with  the  genus  and  order.  In  man 
they  are  very  small,  varying  from  ^^Vo  **^9iToTr  ^^  ^^  ^^^^  ^^  breadth,  while  in 
the  frog  the  long  diameter  of  the  ellipse  measures  at  least  four  times  as  much. 
The  corpuscles  consist  of  an  envelope  containing  a  fluid  in  which  the  red 
colouring-matter  of  the  blood  is  dissolved. 

The  coagulation  of  blood  efi"ects  a  kind  of  natural  proximate  analysis  ;  the 
clear,  pale  serum,  or  fluid  part,  is  an  alkaline  solution  of  albumin,  containing 
various  soluble  salts;  the  clot  is  a  mechanical  mixtm-e  of  fibrin  and  blood 
globules,  swollen  and  distended  with  serum,  of  which  it  absorbs  a  large  but 
variable  quantity. 

When  the  coagulum  of  blood  is  placed  upon  bibulous  paper,  and  drained 
as  much  as  possible  from  the  fluid  portion,  and  then  put  into  water,  the  en- 
velope, which  consists  of  globulin,  dissolves  and  sets  free  the  colouring  matter, 
forming  a  magnificent  crimson  solution,  which  has  many  of  the  characters 
of  a  dye-stuff.  It  contains  albumin  and  globulin,  and  coagulates  by  heat 
and  by  the  addition  of  alcohol ;  this  albumin  and  globulin  cannot  be  sepa- 
rated, and  attempts  to  isolate  the  hematosin  or  red  pigment  have  consequently 
failed.  From  its  extreme  susceptibility  of  change,  it  is  not  known  in  a  state 
of  purity.  The  above  watery  solution,  exposed  with  extensive  surface  in  a 
warm  place,  dries  up  to  a  dark  red,  brittle  mass,  which  is  again  soluble  in 
water.  After  coagulation  it  becomes  quite  insoluble,  but  dissolves  like  albumin 
in'caustic  alkalis.  Cai-bonic  and  sulphurous  acids  blacken  the  red  solution ; 
oxygen,  or  atmospheric  air,  heightens    its  colour ;    protoxide    of  nitrogen 


COMPOSITION    OF    THE    BLOOD.  505 

renders  it  purple ;  while  sulphuretted  hydrogen,  or  an  alkaline  sulphide, 
changes  it  to  a  dirty  greenish  black. 

Hematosin  differs  from  the  other  animal  principles  in  containing  as  an  es- 
sential ingredient  a  remarkable  substance  not  found  elsewhere  in  the  animal 
system,  viz.,  the  oxide  of  the  metal  iron.  If  a  little  of  the  dried  clot  of  blood 
be  calcined  in  a  crucible  and  digested  with  dilute  hydrochloric  acid,  a  solution 
will  be  obtained  rich  in  oxide  of  iron ;  or  if  the  solution  of  colouring  matter 
just  referred  to  be  treated  with  excess  of  chlorine  gas,  the  yellow  liquid 
separated  from  the  greyish  coagulum  formed  will  be  found  to  give  in  a  striking 
manner  the  well-known  reactions  of  the  sesquioxide  of  iron.  There  is  little 
doubt  either  about  the  condition  of  the  metal ;  sesquioxide  of  iron  is  with- 
drawn from  the  dry  clot  by  the  cautious  addition  of  sulphuric  acid,  and 
without  much  alteration  of  the  colour  of  the  mass.*  It  is  well  known  that 
certain  organic  matters,  as  tartaric  acid,  prevent  the  precipitation  of  sesqui- 
oxide of  iron  by  alkalis,  and  its  recognition  by  ferrocyanide  of  potassium, 
and  it  is  very  likely  that  the  blood  may  contain  a  substance  or  substanceaK 
capable  of  doing  the  same. 

Hematosin,  necessarily  in  a  modified  state,  contains,  according  to  Mulder, 
in  100  parts : — 

Carbon  65-3 

Hydrogen 5-4 

Nitrogen  10-4 

Oxygen 11-9 

Iron 70 


1000 


The  following  table  represents  the  composition  of  healthy  human  blood  t 
a  whole  ;  it  is  on  the  authority  of  M.  Lecanu.^ 

(1-)  (2.) 

Water 78015  785-58 

Fibrin 210  3-57 

Albumin 65-09  "69-41 

Colouring  matter 13300  119-63 

Crystallizable  fat 2-43  4-30 

Fluid  fat 1-31  2-27 

1-79  1-92 


Extractive  matter  of  uncertain  nature,  soluble  in 

both  water  and  alcohol 

Albumin  in  combination  with  soda 1-26  2-01 

Chlorides  of  sodium  and  potassium" ;   carbonates,  ")         007  >^.o(\ 

phosphates,  and  sulphates  of  potassaand  soda...  j  ' 

Carbonates  of  lime  and  magnesia;  phosphates  of\        (,,/^  ,  j.^ 

lime,  magnesia,  and  iron  ;  sesquioxide  of  iron...  / 
Loss 2-40  2-59 


1000-00       1000-00 

In  healthy  individuals  of  different  sexes  these  proportions  are  found  to  vary 
slightly,  the  fibrin  and  colouring  matter  being  usually  more  abundant  in  the 
male  than  in  the  female  ;  in  disease,  variations  of  a  far  wider  extent  are  often 
apparent. 

It  appears  singular  that  the  red  corpuscles,  which  are  so  easily  dissolved 
by  water,  should  remain  uninjured  in  the  fluid  portion  of  the  blood.  This 
seems  partly  due  to  the  presence  of  saline  matter,  and  partly  to  that  of  albu  ■ 

*  Liebijr,  Ilandwdrlerbuch,  i.  885.  «  Ann.  Chim.  et  de  Phys.  xlviH.  320 

43 


606  FUNCTION    OF    RESPIRATION. 

min,  the  corpuscles  being  alike  insoluble  in  a  strong  solution  of  salt  and  in  a 
highly  albuminous  liquid.  In  the  blood  the  limit  of  dilution  within  which  the 
corpuscles  retain  their  integrity  appears  to  be  nearly  reached,  for  when 
"water  is  added  they  immediately  become  attacked. 

Closely  connected  with  the  subject  of  tlie  composition  of  the  blood  are  those 
of  respiration,  and  of  the  production  of  animal  heat. 

The  simplest  view  that  can  be  taken  of  a  respiratory  organ  in  an  air-breath- 
ing animal,  is  that  of  a  little  membranous  bag,  saturated  with  moisture,  and 
containing  air,  over  the  surface  of  which  meanders  a  minute  blood-vessel, 
whose  contents,  during  their  passage,-  are  thus  subjected  to  the  chemical 
action  of  the  air  through  the  substance  of  the  membranes,  and  in  virtue  of 
the  solubility  of  the  gaseous  matter  itself  in  the  water  with  which  the  mem- 
branes are  imbued.  In  some  of  the  lower  classes  of  animals,  where  respira- 
tion is  sluggish  and  inactive,  these  air-cells  are  few  and  large  ;  but  in  the 
higher  kinds  they  are  minute,  and  greatly  multiplied  in  number,  in  order  to 
gain  extent  of  surface,  each  communicating  with  the  external  air  by  the  wind- 
pipe and  its  ramifications. 

Respiration  is  performed  by  the  agency  of  the  muscles  which  lie  between 
and  about  the  ribs,  and  by  the  diapliragm.  The  lungs  are  not  nearly  emptied 
of  air  at  each  expiration.  Under  ordinary  circumstances  about  15  cubic 
inches  only  are  thrown  out,  while  by  a  forced  effort  as  much  as  50  or  60 
cubic  inches  may  be  expelled.  This  is  repeated  about  18  times  per  minute 
when  the  individual  is  tranquil  and  undisturbed. 

The  expired  air  is  found  to  have  undergone  a  remarkable  change;  it  is 
loaded  with  aqueous  vapour,  while  a  very  large  proportion  of  oxygen  has 
.disappeared,  and  its  place  been  supplied  by  carbonic  acid  ;  air  once  breathed 
containing  enough  of  that  gas  to  extinguish  a  taper.  The  total  volume  of 
the  air  seems  to  undergo  but  little  change  in  this  process,  the  carbonic  acid 
being  about  equal  to  the  oxygen  lost.  This,  however,  is  found  to  depend 
very  much  upon  the  nature  of  the  food ;  it  is  likely  that  when  fatty  sub- 
stances, containing  much  hydrogen,  are  used  in  large  quantities,  a  disappear- 
ance of  oxygen  will  be  observed.  Nitrogen  is  in  small  quantity  exhaled  from 
the  blood.  In  health  no  nitrogen  is  absorbed  ;  the  food  invariably  containing 
more  of  that  element  than  the  excretions. 

Whatever  may  be  the  difficulties  attending  the  investigation  of  these  sub- 
jects,— and  difficulties  there  are,  as  the  discrepant  results  of  the  experiments 
prove, — one  thing  is  clear;  namely,  that  quantities  of  hydrogen  and  carbon 
are  daily  oxidized  in  the  body  by  the  free  oxygen  of  the  atmosphere,  and 
their  products  expelled  from  the  system  in  the  shape  of  water  and  carbonic 
acid.  Now,  if  it  be  true  that  the  hea»t  developed  in  the  act  of  combination  is 
n  constant  quantity,  and  no  proposition  appears  more  reasonable,  the  high 
temperature  of  the  body  may  be  the  simple  result  of  this  exertion  of  chemi- 
cal force. 

The  oxidation  of  combustible  matter  in  the  blood  is  effected  in  the  capil- 
laries of  the  whole  body,  not  in  the  lungs,  the  temperature  of  which  doe?; 
not  exceed  that  of  the  other  parts.  The  oxygen  of  the  air  is  taken  up  in  the 
lungs,  and  carried  by  the  blood  to  the  distant  capillary  vessels;  by  the  aid 
of  which,  secretion,  and  all  the  mysterious  functions  of  animal  life,  are  un- 
doubtedly performed:  here  the  coynbuation  takes  place,  although  how  this 
happens,  and  what  the  exact  nature  of  the  combustible  may  be,  beyond  the 
simple  fact  of  its  containing  carbon  and  hydrogen,  yet  remains  a  matter  of 
conjecTture.  The  carbonic  acid  produced  is  held  in  solution  by  the  now 
venous  blood,  and  probably  confers,  in  great  measure,  upon  the  latter  its 
dark  colour  and  deleterious  action  upon  the  nervous  system.  Once  more 
poured  into  the  heart,  and  by  that  organ  driven  into  the  second  set  of  capil- 
laries bathed  with  atmospheric  air,  this  carbonic  acid  is  conveyed  outwards. 


FUNCTION    OF    RESPIRATION.  507 

through  the  wet  Tncmbrane,  by  a  kind  of  false  diffusion,  constantly  observed 
under  such  circumstances ;  while  at  the  same  time  oxygen  is,  by  similar 
means,  carried  inwards,  and  the  blood  resumes  its  bright  red  colour,  and  its 
caj^.ability  of  supporting  life.  Much  of  this  oxygen  is,  no  doubt,  simply  dis- 
solved in  the  serum ;  the  corpuscles,  according  to  Professor  Liebig,  act  as 
carriers  of  another  portion,  in  virtue  of  the  iron  they  contain,  that  metal 
being  alternately  in  the  state  of  sesquioxide,  and  of  carbonate  of  the  pro- 
toxide,— of  sesquioxide  in  the  arteries,  and  of  carbonate  of  protoxide  in  the 
veins,  b^-  loss  of  oxygen,  and  acquisition  of  carbonic  acid.  M.  Mulder  con- 
siders the  fibrine  to  act  in  the  same  manner ;  being  true  fibrin  in  the  veins, 
and,  in  part  at  least,  an  oxide  of  proteine  in  the  arteries. 

It  would  be  very  desirable  to  show,  if  possible,  that  the  quantity  of  com- 
bustible matter  daily  burned  in  the  laody  is  adequate  to  the  production  of 
the  heating  effects  observed.  Something  has  been  done  with  respect  to  the 
carbon.  Comparison  of  the  quantities  and  composition  of  the  food  con- 
sumed by  an  individual  in  a  given  time,  and  of  the  excretions,  shows  an 
excess  of  carbon  in  the  former  over  the  latter,  amounting,  in  some  cases, 
according  to  Liebig's  high  estimate,'  to  14  ounces  ;  the  whole  of  which  is 
thrown  off  in  the  state  of  carbonic  acid,  from  the  lungs  and  skin,  in  the 
space  of  twenty-four  hours.  This  statement  applies  to  the  case  of  healthy, 
vigorous  men,  much  employed  in  the  open  air,  and  supplied  with  abundance 
of  nutritious  food.  Females,  and  persons  of  weaker  habit,  who  follow  in- 
door pursuits  in  warm  rooms,  consume  a  much  smaller  quantity ;  their 
respiration  is  less  energetic  and  the  heat  generated  less  in  amount.  Those 
who  inhabit  very  cold  countries  are  well  known  to  consume  enormous  quan- 
tities of  food  of  a  fatty  nature,  the  carbon  and  hydrogen  of  which  are, 
without  doubt,  chiefly  employed  in  the  production  of  animal  heat.  These 
people  live  by  hunting;  the  muscular  exertion  required  quickens  and 
deepens  the  breathing;  while,  from  the  increased  density  of  the  air,  a 
greater  weight  of  oxygen  is  taken  into  the  lungs,  and  absorbed  into  the 
blood  at  each  inspiration.  In  this  manner  the  temperature  of  the  body  is 
kept  up,  notwithstanding  the  piercing  external  cold  ;  a  most  marvellous 
adjustment  of  the  nature  of  the  food,  and  even  of  the  inclinations  and 
appetite  of  the  man,  to  the  circumstances  of  his  existence,  enable  him  to 
bear  Avith  impunity  an  atmospheric  temperature  which  would  otherwise 
injure  him. 

The  carbon  consumed  in  respiration  in  one  day  by  a  horse  moderately 
fed,  amounted,  in  a  valuable  experiment  of  M.  Boussingault,  to  77  ounces ; 
that  consumed  by  a  cow,  to  70  ounces.  The  determination  was  made  in  the 
manner  just  mentioned,  viz.,  by  comparing  the  quantity  and  composition  of 
the  food. 

Chyle. — A  specimen,  examined  by  MM.  Tiedemann  and  Gmelin,  taken 
from  the  thoracic  duct  of  a  horse,  was  found  closely  to  resemble,  in  compo- 
sition and  properties,  ordinary  blood ;  the  chief  difference  was  the  compara- 
tive absence  of  colouiing  matter,  the  chyle  having  merely  a  reddish-white 
tint.  It  coagulated,  after  standing  four  hours,  and  gave  a  red-coloured  clot, 
small  in  quantity,  and  a  turbid,  reddish-yellow  serum.  The  milky  appear- 
ance of  chyle  is  due  to  fat  globules,  which  sometimes  confei  the  same 
chiuacter  upon  the  serum  of  blood. 

LvMPH. — Under  the  name  of  lymph,  two  or  more  fluids,  very  different  in 
their  nature,  have  been  confounded,  namely,  the  fluid  taken  up  by  the  absor- 
bents of  the  alimentary  canal,  which  is  simply  chyle,  containing  both  fibrin 
and  albumin,  and  the  fluid  poured  out,  sometimes  in  prodigious  quantities, 
from  serous  membranes,  which  is  a  very  dilute  solution  of  albumin,  contain 


*  Auim:il  Chemi.stiy,  p.  l-l. 


508  MILK,    BILE,    URINE, 

ing  a  portion  of  soluble  salts  of  the  blood.     The  liquor  amnii  of  the  preg 
nant  female,  and  the  fluid  of  dropsy,  are  of  this  character. 

Mucus  ANn  Pus. — The  slimy  matter  effused  ^lpon  the  surface  of  vnriou!^ 
mucous  membranes,  as  tlie  lining  of  the  alimentary  canal,  that  of  the  blad- 
der, of  the  nose,  lungs,  &c.,  to  which  the  general  name  mitcns  is  given, 
probably  varies  a  good  deal  in  its  nature  in  different  situations.  It  is  com- 
monly either  colourless  or  slightly  yellow,  and  translucent  or  transparent:  it 
is  quite  insoluble  in  water,  forming,  in  the  moist  state,  a  viscid,  gelatinous 
mass.  In  dilute  alkalis  it  dissolves  Avith  ease,  and  the  solution  is  precipi- 
tated by  an  addition  of  acid. 

Pus,  the  natural  secretion  of  a  wounded  or  otherwise  injured  surfixce,  is 
J,.    ...^  commonly  a    creamy,  white,  or    yellowish 

'^*    '"'■  liquid,   which,   under   the   microscope,  ap- 

lP«9\yr.jj!i*(?^      {fSfi^^ijK       pears  to  consist  of  multitudes  of  minute 
©;^#  y     ©gS©       globules   (fig.  175,  «);    dilute  acetic   acid 
^^/t^^/^r^     ^^^^      renders   them  transparent,  and  shows  the 
^(®>vW       @    ^2   W^      internal  nuclei  {b).     It  is  neither  acid  nor 
>>®  ®    ^    4!^    ®  ^      alkaline.     Mixed  with  water,  it  communi- 
^  ^%  ig"^    ®  ff^"5^      c^^^s  ^  milkiness  to  the  latter,  but  after  a 
xsvy^  vi^  ^t^   ^  ^j^^g    subsides.      Caustic    alkali    does   not 

dissolve  pus,  but  converts  it  into  a  trans- 
parent, gelatinous  substance,  which  can  be  drawn  out  into  threads.  The 
peculiar  ropiticss  thus  produced  with  an  alkali  is  not  peculiar  to  pus.  Healthy 
mucus  owes  its  sliminess  to  an  alkaline  fluid  acting  on  the  mucous  globules. 

MILK,    BILE,    URINE,    AND    URINARY   CALCULI. 

Milk. — The  peculiar  special  secretion  destined  for  the  nourishment  of  the 
young  is,  so  far  as  is  known,  very  much  the  same  in  flesh-eating  animals 
and  in  those  which  live  exclusively  on  vegetable  food.  The  proportions  of 
the  constituents  may,  however,  sometimes  differ  to  a  considerable  extent. 
It  will  be  seen  hereafter  that  the  substances  present  in  milk  are  wonderfully 
adapted  to  its  office  of  providing  materials  for  the  rapid  growth  and  develop- 
ment of  the  animal  frame.  It  contains  an  azotized  matter,  casein,  nearly 
identical  in  composition  with  muscular  flesh,  fatty  principles,  and  a  peculiar 
sugar,  and  lastly,  various  salts,  among  which  may  be  mentioned  phosphate 
of  lime,  held  in  complete  solution  in  a  slightly  alkaline  liquid.  This  last  is 
especially  important  to  a  process  then  in  activity,  the  formation  of  bone. 

The  white,  and  almost  opaque,  appearance  of 

*^*    '  '  milk  is  an  optical  illusion ;  examined  by  a  mi- 

^  O  o    *^5  °^  croscope  of  even  modernte  power,  it  is  seen  to 

®  co  (P*  9   o*"*"       o'°^       consist  of  a  perfectly  transparent  fluid,  in  which 

o     o    »•       "^    O"  tf*  ^"•'^*    nbout    numbers    of    transparent    gloludo? 

^o^o^f  o^o^f^SfQO®  (fig-  l'^')«    tJi^'^e  consist  of  fat,  surrounded   by 

®  X^®qSV@°  *^<%<^  *^"  albuminous  envelope,  which  can  be  broken 

^^@o?®    *^  0°  o  *>       mechanically,   as    in   churning,   or  dissolved   by 

^°'^'^^i^^   Q   w^^Q*       *^'^   chemical    action    of   caustic   potassa,   after 

«  o®®."®^®®    ^o  which,  on  agitating  the  milk  with  ether,  the  fat 

"  **  can  be  dissolved. 

When  milk  is  suffered  to  remain  at  rest  some 
hours,  at  the  ordinary  temperature  of  the  air,  a  large  proportion  of  tlie  f<it 
globules  collect  at  the  surface  into  a  layer  of  cream;  if  this  be  now  removed 
and  exposed  for  some  time  to  strong  agitation,  tlie  fat-globules  coalesce  into 
a  mass,  and  the  remaining  watery  liquid  is  expelled  from  between  them  and 
separated.  The  butter  so  produced  must  be  thoroughly  washed  with  cold 
water,  to  remove  as  far  as  possible  the  last  traces  of  casein,  which  readily 
putrefies,  and  would  in  that  case  spoil  the  whole.    A  little  salt  is  usually  added. 


AND    URINARY    CALCULI.  50^ 

OHinary  butter  still,  however,  contains  some  butter-milk,  and  when  in- 
temled  for  kee{iing  should  be  chirified,  as  it  is  termed,  by  fusion.  The 
watery  part  then  subsides,  and  carries  with  it  the  residue  of  the  azotized 
matter.  The  flavour  is  unfortunately  somewhat  impaired  by  this  process. 
The  consistence  of  butter,  in  other  words,  the  proportions  of  margarin  and 
olein,  is  dependent  upon  the  season,  or  more  probably  upon  the  kind  of 
food  ;  in  summer  the  oily  portion  is  always  more  considerable  than  in  win- 
ter. The  volatile  odoriferous  principle  of  butter,  butyrin,  has  been  already 
referred  to. 

The  casein  of  milk,  in  the  state  of  cheese,  is  in  many  countries  an  im- 
portant article  of  food.  The  milk  is  usually  heated  to  about  120°  (49°C), 
and  coagulated  hy  rennet,  or  an  infusion  of  the  stomach  of  the  calf  in  water; 
the  curd  is  carefully  separated  by  a  sieve  from  the  whey,  mixed  with  a  due 
proportion  of  salt,  and  sometimes  some  colouring-matter,  and  then  subjected 
to  strong  and  increasing  pressure.  The  fresh  cheese  so  prepared  being  con- 
stantly kept  cool  and  dry,  undergoes  a  particular  kind  of  putrefactive  fer- 
mentation, very  little  understood,  by  which  principles  are  generated  which 
communicate  a  particular  taste  and  odour.  The  goodness  of  cheese,  as  well 
as  much  of  the  difference  of  flavour  perceptible  in  different  samples,  de- 
pends in  great  measure  upon  the  manipulation ;  the  best  kinds  contain  a 
considerable  quantity  of  fat,  and  are  made  with  new  milk ;  the  inferior 
descriptions  are  made  with  skimmed  milk. 

Some  of  the  Tartar  tribes  prepare  a  kind  of  spirit  from  milk  by  suffering 
it  to  ferment,  with  frequent  agitation.  The  casein  converts  a  part  of  the 
milk-sugar  into  lactic  acid,  and  another  part  into  grape-sugar,  which  in 
turn  becomes  converted  into  alcohol.  Mare's  milk  is  said  to  answer  better 
for  this  purpose  than  that  of  the  cow. 

In  a  fresh  state,  and  taken  from  a  healthy  animal,  milk  is  always  feebly 
alkaline.  When  left  to  itself,  it  very  soon  becomes  acid,  and  is  then  found 
to  contain  lactic  acid,  which  cannot  be  discovered  in  the  fresh  condition. 
Tije  alkalinity  is  due  to  the  soda  which  holds  the  casein  in  solution.  In 
this  soluble  form  casein  possesses  the  power  of  taking  up  and  retaining  a 
very  considerable  quantity  of  phosphate  of  lime.  The  density  of  milk 
varies  exceedingly;  its  quality  usually  bears  an  inverse  ratio  to  its  quantity. 
From  an  analysis  of  cow-milk  in  the  fresh  state  by  M.  Haidlen,'  the  follow- 
ing statement  of  its  composition  in  1000  parts  has  been  deduced  : — 

Water 873-00 

Butter 30  00 

Casein  48-20 

Milk-sugar 43-90 

rhosphate  of  lime 2-31 

'*             magnesia 0  42 

"             iron  007 

Chloride  of  potassium 1-44 

Sodium 0-24 

Soda  in  combination  with  casein 0-42 

1000-00 

Human  milk  k  remarkable  for  the  difficulty  with  which  it  coagulates ;  it 
generally  contains  a  larger  proportion  of  sugar  than  cow-milk,  but  scarcely 
differs  in  other  respects. 

Bilk. — This  is-  a  secretion  of  a  very  different  character  from  .the  pre- 
ceding ;  the  largest  internal  organ  of  the  body,  the  liver,  is  devoted  to  its 


•  Anualcu  dcr  Chemio  unJ  Phurm:if-ie,  xlv.  2G3. 

43* 


510  MILK^    BILE;. URINE, 

preparation,  which  is  said  to  take  place  from  venous,  instead  of  arterial 
blood.  The  composition  of  the  bile  has  been  made  the  subject  of  much  in  • 
vestigation  ;  the  following  is  a  summary  of  the  most  important  facts  which 
have  been  brought  to  light. 

In  its  ordinary  state,  bile  is  a  very  deep  yellow,  or  greenish,  viscid,  trans- 
parent liquid,  which  darkens  by  exposure  to  the  air,  and  undergoes  changes 
which  have  been  yet  imperfectly  studied.  It  has  a  disagreeable  odour,  a 
most  nauseous,  bitter  taste,  a  distinctly  alkaline  reaction,  and  is  miscible 
with  water  in  all  proportions.  When  evaporated  to  dryness  at  212°  (100°C), 
and  treated  with  alcohol,  the  greater  part  dissolves,  leaving  behind  an  in- 
soluble jelly  of  mucus  of  the  gall-bladder.  This  alcoholic  solution  contains 
colouring-matter  and  cholesterin;  from  the  former  it  maybe  freed  by  diges- 
tion with  animal  charcoal,  and  from  the  latter  by  a  large  admixture  of  ether, 
in  which  the  bile  is  insoluble,  and  separates  as  a  thick,  syrupy,  and  nearly 
colourless  liquid.  The  colouring-matter  may  also  be  precipitated  by  baryta- 
water. 

Pure  bile  thus  obtained,  when  evaporated  to  dryness  by  a  gentle  heat, 
forms  a  slightly  yellowish  brittle  mass,  resembling  gum-Arabic.  It  is  com- 
pletely soluble  in  water  and  absolute  alcohol.  The  solution  is  not  affected 
by  the  vegetable  acids  ;  h^^drochloric  and  sulphuric  acids,  on  the  contrary, 
give  rise  to  turbidity,  either  immediately  or  after  a  short  interval.  Acetate 
of  lead  partially  precipitates  it ;  the  tribasic  acetate  precipitates  it  com- 
pletely ;  the  precipitate  is  readily  soluble  in  acetic  acid,  in  alcohol,  and  to  a 
certain  extent  in  excess  of  acetate  of  lead.  When  carbonized  by  heat,  and 
incinerated,  bile  leaves  between  11  and  12  per  cent,  of  ash,  consisting  chiefly 
of  carbonate  of  soda,  with  a  little  common  salt  and  alkaline  phosphate. 
The  recent  beautiful  researches  of  Strecker,  show  that  bile  is  essentially  a 
mixture  of  the  soda-salts  of  two  peculiar  conjugate  acids  very  distinctly 
resembling  the  resinous  and  fatty  acids.  One  of  these  contains  nitrogen, 
but  no  sulphur,  and  is  termed  ckolic  acid,  or  better,  glycho-cholalic,  being  a 
conjugated  compound  of  a  non-nitrogenoiis  acid,  cholalic  acid,^  with  the  nitro- 
genetted  substance  glycocine  (see  page  501),  the  other  containing  nitrogen 
and  sulphur,  has  received  the  name  choleic  acid,  or  better,  tauro-cholalic  acid, 
being  a  conjugated  compound  of  the  same  cholalic  acid  with  a  body  to  be 
presently  described  under  the  name  of  taurin,  containing  both  nitrogen  and 
sulphur.  The  relative  proportion  in  which  these  acids  occur  in  bile,  remains 
pretty  constant  with  the  same  animal,  but  varies  considerably  with  different 
classes  of  animals. 

Glyco-cholalic  acid  may  be  thus  obtained:  —  When  ox  bile  is  perfectly 
dried  and  extracted  with  cold  absolute  alcohol,  and  after  filtration  is  mixed 
with  ether,  it  first  deposits  a  brownish  tough  resinous  mass,  and  after  some 
time,  stellated  crystals  which  consist  of  glyco-cholalate  of  soda  and  potassa. 
These  mixed  crystals  were  first  obtained  by  Platner,  and  they  compose  his 
Bo-called  crystallized  bile. 

Glyco-cholalic  acid  may  be  obtained  by  decomposing  the  glyco-cholalate 
of  soda  by  sulphuric  acid  ;  it  crystallizes  in  fine  white  needles  of  a  bitterish. 
Hweet  taste,  is  soluble  in  water  and  alcohol,  but  only  slightly  in  ether,  and 
has  a  strong  acid  reaction.  It  is  represented  by  the  formula  Cq^H^^^^^i'^O. 
AVhen  boiled  with  a  solution  of  potassa,  the  acid  divides  into  cholalic  acid 
C4,H3gOg,HO,  and  glycocine  or  gelatin-sugar:— 

C52H42NO,„IIO-f2HO    =     C4gH3909,HO-fC4H5N04 

Glyco-cholalic  acid.  Cholalic  acid.    Glycocine. 

'  Also  callpij  cholxc  acid  by  some  authors. 


AND     URINARY     CALCULI.  511 

Boiled  with  concentrated  sulphuric  or  hydrochloric  acids,  it  yields  likewise 
glycocinc,  but  instead  of  cholalic  acid,  another  white  amorphous  acid,  cho- 
loidinic  acid  (C^gHggOg  =  cholalic  acid  —  1  eq.  of  water),  or  if  the  ebullition 
has  continued  for  some  time,  a  resinous  substance,  from  its  insolubility  in 
water  called  dyslysin,  (C48H3g06  =  cholalic  acid  —  4  eq.  of  water.) 

Tauro-cholalic  acid  is  thus  procured.  Ox  bile  is  freed  as  far  as  pos- 
sible from  glyco-cholalic  acid  by  means  of  neutral  acetate  of  lead,  and  it  is 
then  precipitated  by  basic  acetate  of  lead,  to  which  a  little  ammonia  is 
added.  Tlie  precipitate  is  decomposed  by  carbonate  of  soda,  when  tolerably 
purt"  tauro-cholalate  of  soda  is  obtained.  By  decomposing  the  tauro-cholalate 
of  le;ul  by  sulphuretted  hydrogen,  tauro-cholalic  acid  is  liberated.  This 
substance,  however,  which  was  previously  called  choleic  acid  and  bilin,  has 
never  been  obtained  in  the  pure  state.  Its  formula,  as  inferred  from  the 
study  of  its  products  of  decomposition,  would  be  €521144^82053,110.  When 
boiled  with  alkalis  it  divides  into  cholalic  acid  and  taurine: — 

C52H44^^S20,3,IIO  +  2I10     =     C4gIl3909,H04-C4lI,NS,06 


Tauro-cholalic  acid.  Cholalic  acid.       Taurin. 

With  boiling  acids  it  gives  likewise  taurin,  but  instead  of  cholalic  acid, 
either  choloidinic  aci'd  or  dyslysin,  according  to  the  duration  of  the  ebulli- 
tion. 

Taurin,  C4H7NS2O5,  crystallizes  in  colourless  regular  hexagonal  prisms, 
which  have  no  odour  and  very  little  taste.  It  is  neutral  to  test-paper,  and 
permanent  in  the  air.  When  burnt,  it  gives  rise  to  much  sulphurous  acid. 
It  contains  upwards  of  25  per  cent,  of  sulphur.  It  is  easily  prepared  by 
boiling  purified  bile  for  some  hours  with  hydrochloric  acid.  After  filtration 
and  evaporation,  the  acid  residue  is  treated  with  five  or  six  times  its  bulk 
of  boiling  alcohol,  from  which  the  taurin  separates  on  cooling. 

Cholat,ic  or  choltc  acid,  (^43113909,110,  crystallizes  in  tetrahedra.  It 
is  soluble  in  sulphuric  acid,  and  on  the  addition  of  a  drop  of  this  acid  and 
a  solution  of  sugar  (1  part  of  sugar  to  4  parts  of  water),  a  purple-violet 
colour  is  produced,  which  constitutes  Pettenkofer's  test  for  bile.  At  388" 
(195°C)  it  loses  an  atom  of  water,  and  is  converted  into  chloloidinic  acid, 
which  change,  as  has  been  pointed  out,  is  also  produced  by  ebullition  with 
acids. 

Cholalic  acid  is  best  obtained  by  boiling  the  resinous  mass  precipitated  by 
ether  from  the  alcoholic  solution  of  the  bile  with  a  dilute  solution  of  potassa 
for  24  or  35  hours,  till  the  am.orphous  potassa-salt  that  has  separated  begins 
to  crystallize.  The  dark-coloured  soft  mass  removed  from  the  alkaline 
liquid,  diirsolved  in  water,  and  hydrochloric  acid  added,  a  little  ether  causes 
the  deposition  of  the  cholalic  acid  in  crystals. 

One  of  the  colouring-matters  of  the  bile  forms  the  chief  part  of  the  con- 
cretions sometimes  met  with  in  the  gall-bladders  of  oxen,  and  which  are  much 
valued  by  painters  in  water-colours,  as  forming  a  magnificent  yellow  pigment. 
It  dissolves  in  caustic  alkali  without  change  of  colour,  and  when  mixed  with 
excess  of  nitric  acid  becomes  successively  green,  blue,  violet,  red,  and  even- 
tually yellow.  The  composition  of  this  substance  is  unknown.  Auother 
colouring-matter  is  dark  green,  and  is  considered  by  Berzelius,  as  identicaj 
with  the  pigment  of  leaves. 

According  to  the  researches  of  Strecker  and  Gundelach,  pigs'  bile  differs 
from  the  bile  of  other  animals.  This  bile  contains  an  acid,  to  which  the 
name  hyocholic  acid  has  been  given,  which  may  be  prepared  in  the  following 
manner:  — fresh  pigs'  bile  is  mixed  with  a  solution  of  sulphate  of  soda,  the 
precipitate  obtained  is  dissolved  in  absolute  alcohol,  and  decolorized  by 
animal  charcoal.     From  tiiis  solution  ether  throws  down  a  soda-salt,  yield- 


612  MILK,     BILE,     AND     URINE. 

ing,  on  addition  of  sulphuric  ficid,  hj'ocljolic  ncid  as  a  resinous  mass,  which 
is  dissolved  in  alcohol  and  re-precipitated  by  water. 

IJyocholic  acid  contains  Cg4H^3NO,o.  AVhen  heated  Avith  solutions  of  the 
alkalis,  the  acid  undergoes  a  decomposition  perfectly  analogous  to  that  of 
glyco-cholalic  acid,  hyocholic  acid,  splitting  into  glycocine  and  a  crystalline 
acid,  very  soluble  in  alcohol,  less  so  in  ether,  which  has  been  termed  hyocho- 
lalic  acid.  This  substance  contains  CgQllggO^jHO,  and  the  change  is  repre- 
sented by  the  following  equation: — 

^64^43^^010  +  2110       =       C,oH3gO„nO    4-     CJT5NO, 

Hyocholic  acid.  Hyocholalic  acid,     Glycocine. 

Hence  hyocholic  acid  might  be  called  gh/co-hyocholaUc  acid.  When  boiled 
"with  acids,  glyco-hyocholalic  acid  yields  likewise  glycocine,  but  instead  of 
hyocholalic  acid,  a  substance  representing  the  dyslysin  of  the  ordinary  bile, 
"which  might  be  termed  hyodyslysin.  The  composition  of  hyodyslyin  is 
C5{,IT3gOg= hyocholalic  acid  —  2  eq.  HO. 

Pigs'  bile  contains  a  very  trifling  quantity  of  sulphur,  probably  in  the  form 
of  a  sulphuretted  acid  corresponding  to  the  tauro-cholalic  acid  of  ox-bile. 
Strecker  believes  this  acid  to  contain  C54H45N820,2 :  it  might  be  called  taiiro- 
hyocholalic  acid,  which  when  boiled  with  an  alkali  w6uld  yield  taurin  and 
hyocholalic  acid.  The  sulphuretted  acid  must  be  present  in  pigs'  bile  in 
very  minute  quantity :  it  is  even  less  known  than  tauro-cholalic  acid. 

The  once  celebrated  oriental  bczoar- stones  are  biliary  calculi,  said  to  be 
procured  from  a  species  of  antelope;  they  have  a  broAvn  tint,  a  concentric 
structure,  and  a  waxy  appearance,  and  consist  essentially  of  a  peculiar  and 
detiuite  crystallizable  principle  called  lithofcllinic  acid.  To  procure  this  sub- 
stance, the  calculi  are  reduced  to  powder  and  exhausted  with  boiling  al- 
cohol ;  the  dark  solution  is  decolorized  by  animal  charcoal,  and  left  to  eva- 
porate by  gentle  heat,  whereupon  the  lithofcllinic  acid  is  deposited  in  small, 
colourless,  transparent  six-sided  prisms.  It  is  insoluble  in  water,  asd  with 
difhculty  soluble  in  ether,  but  dissolves  with  ease  in  alcohol:  it  melts  at 
202°  (1)5° -SC),  and  at  a  higher  temperature  burns  with  a  smoky  flame, 
leaving  but  little  charcoal.  Lithofelliuic  acid  dissolves  without  decompo- 
sition in  concentrated  acetic  acid,  and  in  oil  of  vitriol;  it  forms  a  soluble 
salt  with  potassa,  and  dissolves  also  in  ammonia,  but  crystallizes  out  un- 
changed on  evaporation.     By  analysis,  lithofelliuic  acid  is  found  to  consist 

Ukink.  —  The  urine  is  the  great  channel  by  which  the  azotized  matter  of 
those  portions  of  the  body  wliich  have  been  taken  up  by  the  absorbents  is 
conveyed  away  and  rejected  from  the  system  in  the  form  of  urea.  It  serves 
also  to  remove  superfluous  water,  and  foreign  soluble  matters  which  get  in- 
troduced into  the  blood. 

The  two  most  remarkable  and  characteristic  constituents  of  urine,  urea 
and  uric  acid,  have  already  been  fully  described ;  in  addition  to  these,  it 
contains  sulphates,  chlorides,  phosphates  of  lime,  and  magnesia,  alkaline 
salts,  and  certain  yet  imperfectly  known  principles,  including  an  odoriferous 
and  a  colouring  substance  (see  foot-note  to  p.  513). 

Healthy  human  urine  is  a  transparent,  light  amber-coloured  liquid,  which, 
while  warm,  emits  a  peculiar,  aromatic,  and  not  disagreeable  odour.  This 
is  lost  on  cooling,  while  the  urine  at  the  same  time  occasionally  becomes 
turbid  from  a  deposition  of  urate  of  ammonia,  which  re-dissolves  with  slijiht 
elevation  of  temperature.  It  is  very  decidedly  acid  to  test-paper ;  •  this 
acidity  has  been  ascribed  to  acid  phosphate  of  soda,  to  free  uric  acid,  and 

*  The  degrwjs  of  acidity  appears  to  be  constantly  changing.    See  Philosophical  Trans.  1849. 


MILK,    BILE,     AND     URINE.  613 

to  free  lactic  acid  ;  laotio  acid  can,  however,  hardly  co-exist  with  urate  of 
ammonia,  and  the  amorphous  buff-coloured  deposit  obtained  from  fresh  urine 
by  spontaneous  evaporation  in  vacuo  is  not  uric  acid,  but  the  ammonia-salt 
of  that  substance,  modified  as  to  crystalline  form  by  the  presence  of  minute 
quantities  of  chloride  of  sodium.  That  a  free  acid  is  sometimes  present  in 
the  urine,  is  certain ;  in  this  case,  the  reaction  to  test-paper  is  far  stronger, 
and  the  liquid  deposits  on  standing  little,  red,  hard  crystals  of  uric  acid ; 
but  this  is  no  longer  a  normal  secretion. 

An  alkaline  condition  of  the  urine  from  fixed  alkali  is  sometimes  met  with. 
Such  alkalinity  can  always  be  induced  by  the  administration  of  neutral 
potassa  or  soda-salts  of  a  vegetable  acid,  as  tartaric  or  acetic  acid ;  the  acid 
of  the  salt  is  burned  iu  the  blood  in  the  process  of  respiration,  and  a  por- 
tion of  the  base  appears  in  the  urine  in  the  state  of  carbonate.  The  urine 
is  often  alkaline  in  cases  of  retention,  from  carbonate  of  ammonia  produced 
by  putrefaction  in  the  bladder  itself;  but  this  is  easily  distinguished  from 
alkalinity  from  fixed  alkali,  in  which  it  is  secreted  in  that  condition. 

The  density  of  the  urine  varies  from  1-005  to  1-030;  about  1-020  to  1-023 
may  be  taken  as  the  average  specific  gravity.  A  high  degree  of  density  iu 
urine  may  arise  from  an  unusually  large  proportion  of  urea;  in  such  a  case, 
the  addition  of  nitric  acid  will  occasion  an  almost  immediate  production  of 
crystals  of  nitrate  of  urea,  whereas  with  urine  of  the  usual  degree  of  con- 
centration many  hours  will  elapse  before  the  nitrate  begins  to  separate.  The 
quantity  passed  depends  much  upon  circumstances,  as  upon  the  activity  of 
the  skin ;  it  is  usually  more  deficient  in  quantity  and  of  higher  density  in 
summer  than  in  winter.  Perhaps  about  32  ounces  in  the  24  hours  may  be 
assumed  as  a  mean. 

When  kept  at  a  moderate  temperature,  urine,  after  some  days,  begins  to 
decompose ;  it  exhales  an  offensive  odour,  becomes  alkaline  from  the  pro- 
duction of  carbonate  of  ammonia,  and  turbid  from  the  deposition  of 
earthy  phosphates.  The  carbonate  of  ammonia  is  due  to  the  putrefactive 
decomposition  of  the  urea,  which  gradually  disappears,  the  ferment,  or  active 
agent  of  the  change,  being  apparently  the  mucus  of  the  bladder,  a  portion 
of  which  is  always  voided  with  the  urine.  It  has  been  found  also  that  the 
yellow  adhesive  deposit  from  stale  urine  is  a  most  powerful  ferment  to  the 
fresh  secretion.  In  this  putrefied  state  urine  is  used  in  several  of  the  arts, 
as  in  dyeing ;  and  forms,  perhaps,  the  most  valuable  manure  for  land  known 
to  exist. 

Putrid  urine  always  contains  a  considerable  quantity  of  sulphide  of  am- 
monium ;  this  is  formed  by  the  de-oxidation  of  sulphates  by  the  organic 
matter.  The  highly  offensive  odour  and  extreme  pungency  of  the  decom- 
posing liquid  may  be  prevented  by  previously  mixing  the  urine,  as  Liebig 
suggests,  with  sulphuric  or  hydrochloric  acid,  in  sufficient  quantity  to  satu- 
rate all  the  ammonia  that  can  be  formed. 

The  following  is  an  analysis  of  human  urine,  by  Berzelius.  1000  partft 
contained 

Water 93300 

Urea  3010 

Lactates  and  extractive  matter' 17-14 

•  All  dark-coloured,  uncryptallizable  substanres,  soluble  both  in  water  and  al'"ohol,  were 
confounded  by  the  old  chemists  under  the  general  name  of  extractive  matter.  The  progress 
of  modern  science  constantly  tends  to  extricate  from  this  confused  mass  one  by  one  the 
many  definite  organic  principles  therein  contained  in  a  more  or  less  motlified  form,  and  to 
restrict  within  narrower  limits  the  application  of  the  term.  In  the  above  instance,  the 
colouring  matter  of  the  larine,  and  it  may  be  several  other  substances,  are  involved. 

Professor  Liebig  states  that  all  his  endeavours  to  obtain  direct  evidence  of  the  existence 
of  lactic  acid  in  the  uriue,  either  in  a  fresh  or  putrid  state,  completely  failed.    Putrid  uriQ« 


5U 


MILK,     BILE,     AND     URINE. 

Uric  acid  100 

Sulphates  of  potassa  and  soda  6  87 

Phosphate  of  soda 2-92 

"                ammonia 1-65 

*'               lime  and  magnesia  1-00 

Chloride  of  sodium  4-45 

Sal-ammoniac '. 1-50 

Silica 003 

Mucus  of  bladder 032 


100000 


Fig.  1^ 


In  certain  states  of  disorder  and  disease  substances  appear  in  the  urine 
which  are  never  present  in  the  normal  secretion;  of  these  the  most  common 
is  albumin.  This  is  easily  detected  by  the  addition  of  nitric  acid  in  excess, 
which  then  causes  a  white  cloud  or  turbidity,  which  is  permanent  when 
boiled,  or  by  corrosive  sublimate,  the  urine  being  previously  acidified  by  a 
little  acetic  acid ;  boiling  causes  usually  a  precipitate  which  is  not  dissolved, 
by  a  drop  or  two  of  acid.  Mere  turbidity  by  boiling  is  no  proof  of  albumin, 
tl>3  earthy  phosphates  being  often  thrown  down  from  nearly  neutral  urine 
u^der  such  circumstances ;  the  phosphatic  precipitate  is,  however,  instantly 
dissolved  by  a  drop  of  nitric  acid. 

in  diabetes  the  urine  contains  grape-sugar,  the  quantity  of  which  com- 
monly increases  with  the  progress  of  the  disease, 
until  it  becomes  enormous,  the  urine  acquiring  a 
density  of  1040  and  beyond.  It  does  not  appear 
that  the  urea  is  deficient  alsoluteb/,  although 
more  difficult  to  discover  from  being  mixed  with 
such  a  mass  of  syrup.  The  smallest  trace  of 
sugar  maj'  be  discovered  in  urine  by  Tromraer's 
test,  (fig.  177,)  formerly  mentioned  :  a  few  drops 
of  solution  of  sulphate  of  copper  are  added  to 
the  urine,  and  afterwards  an  excess  of  caustic 
potassa  ;  if  sugar  be  present,  a  deep-blue  liquid 
results,  which,  on  boiling,  deposits  red  suboxide 
of  copper.  With  proper  management,  this  test 
is  very  valuable ;  it  will  even  detect  sugar  in  the 
blood  of  diabetic  patients.'  Urine  containing 
sugar,  when  mixed  with  a  little  yeast,  and  put 
in  a  warm  place,  readily  undergoes  vinous  fer- 
mentation, and  afterwards  yields,  on  distillation, 
weak  alcohol,  contaminated  with  ammonia. 
^  The  urine  of  children  is  said  sometimes  to  contain  benzoic  acid ;  it  is  pos- 
Bible  that  this  may  be  hippuric  acid.  When  benzoic  acid  is  taken,  the  urine 
after  a  few  hours  yields  on  concentration,  and  the  addition  of  hydrochloric 
acid,  needles  of  hippuric  acid,  soiled  by  adhering  uric  acid. 

yielded  a  volatile  acid  in  a  notable  quantity,  which  turned  out  to  be  acetic  acid;  a  little  ben- 
zoic acid  was  also  noticed,  and  traced  to  a  small  amount  of  hippuric  acid  in  the  recent  urine. 
The  acid  reaction  of  urine  is  ascribed  to  an  acid  phosphate  of  soda,  produced  by  the  partial 
Wecomposition  of  some  of  the  common  phosphate,  the  reaction  of  which  is  alkaline,  by  the 
organic  acids  (uric  and  hippuric)  generated  in  the  system,  aided  by  the  sulphuric  acid  con- 
.itantly  produced  by  the  oxidation  of  the  protein-compounds  of  the  food,  or  rather  of  the 
body. — Lancet,  June.  1814. 

Still  more  recently  Llebig  has  announced  the  discovery  in  the  urine  of  kreatin  and  krea- 
tinine,  already  descriVod.     Putrid  urine  contains  kreatinine  only. 

'  Dr.  Bencc  Jones,  Med.  Chirur.  Trans,  vol.  xxvi.  Great  care  must  be  taken  in  nsinj^thia 
*«!.^t.  which  depcnils  on  the  instantaneous  reiluction  of  the  oxide  of  copper.  By  long  boiling 
rery  many  organic  substances  pi-oduce  this  reaction. 


URINARY    CALCULI 


515 


The  deposit  of  buff-coloured  or  pinkish  amorphous  urate  of  ammonia, 
which  so  fi-equently  occurs  in  urine  upon  cooling,  after  unusual  exercise  or 
Bliglit  derangements  of  health,  may  be  at  once  distinguished  from  a  deposit 
of  ammonio-magnesian  pliospliate  by  its  instant  disappearance  on  the  appli- 
cation of  heat.  Tlie  earthy  phosphates,  besides,  are  hardly  ever  deposited 
from  urine  which  has  an  acid  reaction.  The  nature  of  the  red  colouring 
mutter  which  so  often  stains  urinary  deposits,  especially  in  the  case  of  free 
uric  acid,  is  yet  unknown. 

The  yellow  principle  of  bile  has  been  observed  in  urine  in  severe  cases  of 
jaundice. 

The  urine  of  the  carnivorous  mammifera  is  small  in  quantity,  and  highly 
acid ;  it  'has  a  very  offensive  odour,  and  quickly  putrefies.  In  composition 
it  resembles  that  of  man,  and  is  rich  in  urea.  In  birds  and  serpents  the 
uriue  is  a  white  pasty  substance,  consisting  almost  entirely  of  urate  of  ammo- 
nia. In  herbivorous  animals  it  is  alkaline  and  often  turbid  from  earthy  car- 
bonates and  phosphates  ;  urea  is  still  the  chai-acteristic  ingredient,  while  of 
uric  acid  there  is  scarcely  a  trace;  hippuric  acid  is  usually,  if  not  always, 
present,  sometimes  to  a  very  large  extent.  AVhen  the  urine  putrefies,  this 
hippuric  acid,  as  already  noticed,  becomes  changed  to  benzoic  acid. 

Urinary  calculi. ^Stouy  concretions,  differing  much  in  physical  charac- 
ters and  in  chemical  composition,  are  unhappily  but  too  frequently  formed 
in  the  bladder  itself,  and  give  rise  to  one  of  the  most  distressing  complaints 
to  which  humanity  is  subject.  Although  many  endeavours  have  been  made 
to  find  some  solvent  or  solvents  for  these  calculi,  and  thus  supersede  the 
necessity  of  a  formidable  surgical  operation  for  their  removal,  success  has 
been  but  very  partial  and  limited. 

Urinary  calculi  are  genei'ally  composed  of  concentric  layers  of  crystalline 
or  amorphous  mattei%  of  various  degrees  of  hardness.  Very  frequently  the 
central  point  or  nucleus  is  a  small  foreign  body;  curious  illustrations  of  this 
"will  be  seen  in  any  large  collection.  Calculi  are  not  confined  to  man;  the 
lower  animals  are  subject  to  the  same  affliction;  they  have  been  found  in 
horses,  oxen,  sheep,  pigs,  and  almost  constantly  in  rats. 

The  following  is  a  sketch  of  the  principal  characters  of  the  different  varie- 
ties of  calculi : — 

1.  Uric  Acid. — These  are  among  the  most  common;  externally  they  are 
smooth  or  warty,  of  yellowish  or  brownish  tint ; 
they  liave  an  imperfectly  crystalline,  dis- 
tinctly concentric  structure,  and  are  tolerably 
hard.  Fig.  178.-  Before  the  blowpipe  the  uric 
acid  calculus  burns  away,  leaving  no  ash.  It 
is  insoluble  in  water,  but  dissolves  with  f:icility 
in  caustic  potassa,  with  but  little  ammoniacal 
odour;  the  solution  mixed  with  acid  gives  a 
copious  white  curdy  precipitate  of  uric  acid, 
which  speedily  becomes  dense  and  crystalline. 
Cautiously  heated  with  nitric  acid,  and  then 
mixed  willi  a  little  ammonia,  it  gives  the  cha- 
racteristic reaction  of  uric  acid,  viz.,  deep  pur- 
ple-red murexide. 

2.  Urate  of  Ammonia. — Calculi  of  urate  of 
ammonia  much  resemble  the  preceding ;  they 
are  easily  distinguished,  however.  Fig,  179, 
The  powder  boiled  in  water  dissolves,  and  the 
solution  gives  a  precipitate  of  uric  acid  when 
niixed  with  hydrochloric  acid.  It  dissolves 
also  in  hot  carbonate  of  potassa  with  copious 
'"•volution  of  ammonia. 


Fig.  178. 


Fii,^  179. 


618 


URINARY    C  ALCU  LI. 


Fig.  180. 


Fig.  181. 


3.  Fusible  Calculus ;  Fhosphate  of  Lime  tvith  Fhos^phate  of  Magnesia  and 
Ammonia. — This  is  one  of  the  most  common  kinds. 
The  stone?  are  usually  white  or  pale-coloured, 
smooth,  earthy,  and  soft ;  they  often  attain  a 
large  size.  Fig.  180.  Before  the  blowpipe  this 
substance  blackens  from  animal  matter  which 
earthy  calculi  always  contain ;  then  becomes 
white,  and  melts  to  a  bead  with  comparative 
facility.      It  is  insoluble   in   caustic   alkali,   but 

•  readily  soluble  in  dilute  acids,  and  the  solution 

Is  precipitated  by  ammonia.  Calculi  of  unmixed  phosphate  of  lime  are  rare, 
as  also  those  of  phosphate  of  magnesia  and  ammonia ;  the  latter  salt  is 
Bometimes  seen  forming  small,  brilliant  crystals  in  cavities  in  the  fusible 
calculus. 

4.  Oxalate  of  Lime  Calculus;  Mulberry  Calculus. — The  latter  name  is  de- 
rived from  the  rough,  warty  character,  and  dai-k 
blood-stained  aspect  of  this  variety;  it  is  perhaps 
the  worst  form  of  calculus.  Fig.  181.  It  is  ex- 
ceedingly hard ;  the  layers  are  thick  and  imper- 
fectly crystalline.  Before  the  blowpipe  the  oxa- 
late of  lime  burns  to  carbonate  by  a  moderate 
red-heat,  and,  when  the  flame  is  strongly  urged, 
to  quicklime.  It  is  soluble  in  moderately  strong 
hydrochloric  acid  by  heat,  and  very  easily  in  ni- 
tric acid.  When  finely  powdered  and  long  boiled 
in  a  solution  of  carbonate  of  potassa,  oxalate  of 

potassa  may  be  discovered  in  the  filtered  liquid, 
when  carefully  neutralized  by  nitric  acid,  by  white  precipitates  with  solu- 
tions of  lime,  lead,  and  silver.  A  sediment  of  oxalate  of  lime  in  very  minute, 
transparent,  octahedral  crystals,  only  to  be  seen  by  the  microscope,  is  of 
common  occurrence  in  urine  in  which  a  tendency  to  urate  of  ammonia 
deposits  exists, 

6.  Cystic  and  Xanthic  Oxides  have  already  been  described :  they  are  very 
rare,  especially  the  latter.  Calculi  of  cystic  oxide  are  very  crystalline,  and 
often  present  a  waxy  appearance  externally ;  sediments  of  cystic  oxide  are 
sometimes  met  with.  As  before  mentioned,  this  substance  is  a  definite  crys- 
tallizable  organic  principle,  containing  sulphur  to  a  large  amount ;  it  is  solu- 
ble both  in  acids  and  alkalis.  When  the  solution  in  nitric  acid  is  evaporated 
to  dryness,  it  blackens ;  when  dissolved  in  a  large  quantity  of  caustic  potassa, 
a  drop  of  solution  of  acetate  of  lead  added,  and  the  whole  boiled,  a  black  pre- 
cipitate containing  sulphide  of  lead  makes  its  appearance.  By  these  charac- 
ters cystic  oxide  is  easily  recognized. 

Xanthic  oxide,  also  a  definite  organic  principle,  is  distinguished  by  the 
peculiar  deep-yellow  colour  produced  when  its  solution  in  nitric  acid  is  evapo- 
rated to  dryness  ;  it  is  soluble  in  alkalis,  but  not  in  hydrochloric  acid. 

Very  many  calculi  are  of  a  composite  nature,  the  composition  of  the  dif- 
ferent layers  being  occasionally  changed,  or  alternating ;  thus,  urate  of  am- 
monia and  oxalate  of  lime  are  not  unfrequently  associated  in  the  same 
Btont. 


NERVOUS    SUBSTANCE  ;    MEMBRANOUS    TISSUE  ;    BONES. 

Nervous  substance,  —  The  brain  and  nerves  consist  of  an  albuminous 
substance,  containing  several  remarkable  fatty  principles,  capable  of  being 
extracted  by  alcohol  and  ether,  some  of  which  are  yet  very  imperfectly 
known,  and  about  80  per  cent,  of  water.  Besides  cholesterin,  and  a  little 
ordinary  fat,  separated  in  the  manner  mentioned,  M.  Fr^my  describes  two 


MEMBRANOUS    TISSUES.  617 

new  bodies,'  cerebric  acid  and  oho-phosphoric  acid.  The  first  is  solid,  white, 
and  ci'ystalline,  soluble  without  difficulty  in  boiling  alcohol,  and  forming 
with  hot  water  a  soft,  gelatinous  mass.  It  melts  when  heated,  and  decom- 
poses almost  immediately  afterwards,  exhaling  a  peculiar  odour,  and  leaving 
a  quantity  of  charcoal  which  contains  free  phosphoric  acid,  and  is  in  conse- 
quence very  difficult  to  bui'n.  It  combines  with  the  alkalis,  but  forms  in- 
soluble compounds.     Cerebric  acid  contains  in  100  parts  — 

Carbon 66-7 

Hydrogen 20-6 

Nitrogen  , 2-3 

Oxygen 195 

Phosphorus 0-9 

100-0 
The  oleo-phosphoric  acid  has  been  even  less  perfectly  studied  than  the 
preceding  substance.     It  is  of  soft  oily  consistence,  soluble  in  hot  alcohol 
and  ether,  and  saponifiable.     When  boiled  with  water,  it  is  resolved  into  a 
fluid  neutral  oil,  called  cerebrolein,  and  phosphoric  acid,  which  dissolves. 

The  oily  matter  of  the  brain  is  sufficient  in  quantity  to  form  with  the 
albuminous  portion  a  kind  of  emulsion,  which,  when  beaten  up,  remains 
long  suspended  in  water. 

Membranous  tissues  ;  skin.  —  The  composition  of  the  many  gelatin- 
giving  tissues  of  the  body  is  in  great  measure  unknown  ;  even  that  of  gela- 
tin itself  is  very  doubtful,  as  several  different  substances  may  very  possibly 
be  confounded  under  this  name.  Dr.  Scherer*  has  given,  among  many 
others,  analyses  of  the  middle  coat  of  the  arteries,  which  will  serve  as  an 
example  of  a  finely  organized,  highly  elastic  membrane,  and  of  the  coarse 
epidermis  of  the  sole  of  the  foot,  with  which  it  may  be  contrasted : — 

Artery  coat.  Epidermis. 

Carbon 53-75  61-04 

Hydrogen 708  6-80 

Nitrogen 15-36  17-23 

Oxygen 23  81  24-93 

100-00  100-00 

A  little  sulphur  was  found  in  the  epidermis.  Hair,  horn,  nails,  wool,  and 
feathers  have  a  nearly  similar  composition  ;  they  all  dissolve  with  disen- 
gagement of  ammonia  in  caustic  potassa,  and  the  solution,  when  mixed  with 
acid,  deposits  a  kind  of  protein  common  to  the  whole.  It  is  useless  assign- 
ing foi-mulse  to  substances  yet  so  little  understood. 

The  principle  of  tanning,  of  such  great  practical  value,  is  easily  explained. 
When  the  skin  of  an  animal,  carefully  deprived  of  hair,  fat,  and  other  im- 
purities, is  immersed  in  a  dilute  solution  of  tannic  acid,  the  animal  matter 
gradually  combines  with  that  substance  as  it  penetrates  inwards,  forming  a 
perfectly  insoluble  compound,  which  resists  putrefaction  completelj' ;  this  is 
leather.  In  practice,  lime-water  is  used  for  cleansing  and  preparing  the 
skin,  and  an  infusion  of  oak-bark,  or  sometimes  catechu,  or  other  astringent 
matter,  for  the  source  of  tannic  acid.  The  process  itself  is  necessarily  a 
slow  one,  as  dilute  solutions  only  can  be  safely  used.  Of  late  years,  how- 
ever, vai-ious  contrivances,  some  of  which  shoAV  great  ingenuity,  have  been 
adopted  with  more  or  less  success,  for  quickening  the  operation.  All  leather 
is  not  tanned  ;    glove-leather  is  dressed  with  alum  and  common   salt,  and 

'  Ann.  Chim  et  Pbyp.  3rd  series,  ii.  463. 

"  Anna]  en  der  Chomie  und  rharmacic;  xl.  50. 

44 


618  ANIMAL     NUTRITION. 

afterwards  treated  with  a  preparation  of  the  yolks  of  eggs,  which  contain 
an  albuminous  matter-  and  a  yellow  oil.  Leather  of  this  kind  still  yields  a 
size  by  the  action  of  boiling  water. 

Boxes.  —  Bones  are  constructed  of  a  dense  celliilar  tissue  of  membra- 
nous matter,  made  stiff  and  rigid  by  insoluble  earthy  salts,  of  which  phos- 
phate of  lime  (SCaOjPOg)  is  the  most  abundant.  Tlie  proportions  of  earthy 
and  animal  matter  vary  very  much  with  the  kind  of  bone  and  with  the  age 
of  the  individual,  as  will  be  seen  in  the  following  table,  in  which  the  corres- 
ponding bones  of  an  adult  and  of  a  still-born  child  are  compared : — 

ADULT.  CHILD. 


Inorganic      Organic  Inorganic  Organic 

matter.         matter.  matter.  matter. 

Femur 62-49  ...  87-51  57-51   ...  42-49 

Humerus 63  02  ...  30-98  58  08  ...  41-92 

Radius 60-51  ...  89-49  56-50  ...  43-50 

Os  temporum 63-50  ...   30-50  55-90  ...  44-10 

Costa 67-49  ...  42-51  53-75  ...  46-25 

The  bones  of  the  adult  being  constantly  richer  in  earthy  salts  than  those  of 
the  infant. 

The  following  complete  comparative  analysis  of  human  and  ox-bones  ia 
due  to  Berzelius : — 

Human  bones.        Ox-bones. 


Animal  matter  soluble  by  boiling  ....  32-17  ")               ^q.90 

Vascular  substance 1-13/  

losphate  of  lime,  with  a  little  )  ro  m                 tt  or 

uoride  oi  calcium / 


Ph( 
ill 

Carbonate  of  lime 11-30  3-85 

Phosphate  of  magnesia 1-16   2-05 

Soda,  and  a  little  common  salt 1-20  8-45 


10000  10000 

The  teeth  have  a  very  similar  composition,  but  contain  less  animal  matter ; 
their  texture  is  much  more  solid  and  compact.  The  enamel  does  not  contain 
more  than  2  or  3  per  cent,  of  animal  matter. 

ON  THE  FUNCTION  OF  NUTRITION  IN  THE  ANIMAL  AND  VEGETABLE  KINGDOMS. 

The  constant  and  unceasing  waste  of  the  animal  body  in  the  process  of 
respiration,  and  in  the  various  secondary  changes  therewith  connected,  ne- 
cessitates an  equally  constant  repair  and  renewal  of  the  whole  frame  by  the 
deposition  or  organization  of  matter  from  the  blood,  which  is  thus  gradually 
impoverished.  To  supply  this  deficiency  of  solid  material  in  the  circulating 
fluid  is  the  office  of  the  food.  The  sti-iking  contrast  which  at  first  appears 
in  the  nature  of  the  food  of  the  two  great  classes  of  animals,  the  vegetable 
feeders  and  the  carnivorous  races,  diminishes  greatly  on  close  examination  : 
it  will  be  seen,  that,  so  far  as  the  materials  of  blood,  or,  in  other  words, 
those  devoted  to  the  repair  and  sustenance  of  the  body  itself,  are  concerne  i, 
the  process  is  the  same.  In  a  flesh-eating  animal  great  simplicity  is  observed 
in  the  construction  of  the  digestive  organs:  the  stomach  is  a  mere  enlarge- 
ment of  the  short  and  simple  alimentary  canal ;  and  the  reason  is  plain :  thf 
food  of  the  creature,  flesh,  is  absolutely  identical  in  composition  with  its 
own  blood,  and  with  the  body  that  blood  is  destined  to  nourish.  In  tiie  sto- 
mach it  undergoes  mere  solution,  being  brought  into  a  state  fitted  for  absorp- 
tion by  the  lacteal  vessels,  by  which  it  is  nearly  all  taken  up,  and  at  once 
conveyed  into  the  blood;  the  excrements  of  such  animals  are  little  more 


ANIMAL     NUTRITION.  519 

than  the  comminuted  bones,  feathers,  hair,  and  other  matters  which  refuse 
to  dissolve  in  the  stomach.  The  same  condition,  that  the  food  employed  for 
tlie  nourishment  of  the  body  must  have  the  same  or  nearly  the  same  chen)i- 
cal  composition  as  the  body  itself,  is  really  fulfilled  in  the  case  of  animals 
that  live  exclusively  on  vegetable  substances.  It  has  been  shown'  that  cer- 
tain of  the  azotized  principles  of  plants,  which  often  abound,  and  are  never 
altogether  absent,  have  a  chemical  composition  and  assemblage  of  properties 
which  assimilate  them  in  the  closest  manner,  and  it  is  believed  even  identify 
them,  with  the  azotized  principles  of  the  animal  body ;  vegetable  albumin, 
fibrin,  and  casein  are  scarcely  to  be  distinguished  from  the  bodies  of  the  same 
name  extracted  from  blood  and  milk. 

If  a  portion  of  wheaten  flour  be  made  into  a  paste  with  water,  and  cau- 
tiously washed  on  a  fine  metallic  sieve,  or  in  a  cloth,  a  greyish,  adhesive, 
elastic,  insoluble  substance  will  be  left,  called  gluten  or  glutin,  and  a  milky 
liquid  will  pass  through,  which  by  a  few  hours'  rest  becomes  clear  by  de- 
positing a  quantity  of  starch.  If  now  this  liquid  be  boiled,  it  becomes  again 
turbid  from  the  production  of  a  flocculent  precipitate,  which,  when  collected, 
washed,  dried,  and  purified  from  fat  by  boiling  with  ether,  is  found  to  have 
the  same  composition  as  animal  albumin.  The  glutin  itself  is  a  mixture  of 
true  vegetable  fibrin,  and  a  small  quantity  of  a  peculiar  azotized  matter 
called  gliadin,  to  which  its  adhesive  properties  are  due.  The  gliadin  may 
be  extracted  by  boiling  alcohol,  together  with  a  thick,  fluid  oil,  which  is 
separable  by  ether ;  it  is  gluey  and  adhesive,  quite  insoluble  in  water,  and, 
when  dry,  hard  and  translucent  like  horn ;  it  dissolves  readily  in  dilute  caus- 
tic alkali,  and  also  in  acetic  acid.  The  fibrin  of  other  grain  is  unaccompa- 
nied by  gliadin ;  barley  and  oatmeal  yield  no  glutin,  but  incoherent  filaments 
of  nearly  pure  fibrin. 

Vegetable  albumin  in  a  soluble  state  abounds  in  the  juice  of  many  soft 
succulent  plants  used  for  food ;  it  may  be  extracted  from  potatoes  by  mace- 
rating the  sliced  tubers  in  cold  water  containing  a  little  sulphuric  acid.  It 
coagulates  when  heated  to  a  temperatm-e  dependent  upon  the  degree  of  con- 
centration, and  cannot  be  distinguished  when  in  this  state  from  boiled  white 
of  egg  in  a  divided  condition. 

Almonds,  peas,  beans,  and  many  of  the  oily  seeds,  contain  a  principle 
which  bears  the  most  striking  reseinblance  to  the  casein  of  milk.  When  a 
solution  of  this  substance  is  heated,  no  coagulation  occurs,  but  a  skin  forms 
on  the  surface,  just  as  with  boiled  milk.  It  is  coagulable  by  alcohol,  and  by 
acetic  acid  :  the  last  being  a  character  of  importance.  Such  a  solution  mixed 
with  a  little  sugar,  an  emulsion  of  sweet  almonds,  for  instance,  left  to  itself, 
soon  becomes  sour  and  curdy,  and  exhales  an  offensive  smell ;  it  is  then  found 
to  contain  lactic  acid. 

All  these  substances  dissolve  in  caustic  potassa  with  production  of  a  small 
quantity  of  alkaline  sulphide;  the  filtered  solutions  mixed  with  excess  of 
acid  give  precipitates  of  protein. 

The  following  is  the  composition  in  100  parts  of  vegetable  albumin  and 
fibrin  ;  it  will  be  seen  that  they  agree  very  closely  with  the  results  before 
given:  — 

Albumin.  Fibrin. 

Carbon 5501  54-60 

Hydrogen 7-23  7-30 

Nitrogen 15-92  15-81 

Oxygen,  sulphur,  and  phosphorus 21-84  22-29 

10000  10000 


Liebig,  Ann.  der  Cbeni.  uud  riiarm.  xxxix.  129. 


520  ANIMAL    NUTRITION. 

The  composition  of  vegetable  casein,  or  legumin,  has  not  been  so  well  ma-la 
out;  so  much  discrepancy  appears  in  the  analyses  as  to  lead  to  the  suppo- 
sition  that  different  substances  have  been  operated  upon. 

The  great  bulk,  however,  of  the  solid  portion  of  the  food  of  the  herbivora 
consists  of  bodies  which  do  not  contain  nitrogen,  and  therefore  cannot  yield 
tjustenance  in  the  manner  described  :  some  of  these,  as  vegetable  fibre  or  lig- 
nin,  and  waxy  matter,  pass  unaltered  through  the  alimentary  canal ;  others, 
as  starch,  sugar,  gum,  and  perhaps  vegetable  fat,  are  absorbed  into  the  sys- 
tem, and  afterAvards  disappear  entirely:  they  are  supposed  to  contribute 
very  largely  to  the  production  of  animal  heat. 

On  these  principles.  Professor  Liebig '  has  very  ingeniously  made  the  dis- 
tinction between  what  he  terms  plastic  elements  of  nutrition  and  elements  of 
respiration  ;  to  the  former  class  belong 

Vegetable  fibrin, 
Vegetable  albumin, 
Vegetable  casein, 
Animal  flesh. 
Blood. 


To  the  latter, 
Fat, 
Starch, 
Gum, 
Cane-sugar, 


Grape-sugar, 
Milk-sugar, 
Pectine, 
Alcohol  ? 


In  a  flesh-eating  animal  the  waste  of  the  tissues  is  very  rapid,  the  tem- 
perature being,  as  it  were,  kept  up  in  great  measure  by  the  burning  of 
azotized  matter ;  in  a  vegetable  feeder  it  is  probably  not  so  great,  the  nou' 
azotized  substances  being  consumed  in  the  blood  in  the  place  of  the  organic 
fabric. 

When  the  muscular  movements  of  a  healthy  animal  are  restrained,  a  genial 
temperature  kept  up,  and  an  ample  supply  of  food  containing  much  amyla- 
ceous or  oily  matter  given,  an  accumulation  of  fat  in  the  system  rapidly  takes 
place ;  this  is  well-seen  in  the  case  of  stall-fed  cattle.  On  the  other  hand, 
when  food  is  deficient,  and  much  exercise  is  taken,  emaciation  results.  These 
efi'ects  are  ascribed  to  difference  in  the  activity  of  the  respiratory  function ; 
in  the  first  instance,  the  heat-food  is  supplied  faster  than  it  is  consumed,  and 
hence  accumulates  in  the  form  of  fat;  in  the  second,  the  conditions  are  re- 
versed, and  the  creature  is  kept  in  a  state  of  leanness  by  its  rapid  con- 
sumption. The  fat  of  an  animal  appears  to  be  a  provision  of  nature  for  the 
maintenance  of  life  during  a  certain  period  under  circumstances  of  privation. 

The  origin  of  fat  in  the  animal  body  has  recently  been  made  the  subject 
of  much  animated  discussion ;  on  the  one  hand  it  was  contended  that  satis- 
factory evidence  exists  of  the  conversion  of  starch  and  saccharine  substances 
into  fat,  by  separation  of  carbon  and  oxygen,  the  change  somewhat  resem- 
bling that  of  vinous  fermentation :  it  was  argued,  on  the  other  side,  that  oily 
or  fatty  matter  is  invariably  present  in  the  food  supplied  to  the  domestic  ani- 
mals, and  that  this  fat  is  merely  absorbed  and  deposited  in  the  body  in  a 
slightly  modified  state.  The  question  has  now  been  decided  in  favour  of  the 
first  of  these  views,  which  was  enunciated  by  Professor  Liebig,  by  the  very 
chemist  who  formerly  advocated  the  second  opinion.  By  a  series  of  very 
Oeautiful  experiments,  MM.  Dumas  and  Milne  Edwards  proved  that  bees 
exclusively  feeding  upon  sugar  were  still  capable  of  producing  wax,  whicli 
was  pointed  out  as  a  veritable  fact. 

•  Auiinal  Chemistry,  p.  96. 


ANIMAL    NUTRITION.  -621 

It  is  not  known  in  what  manner  di(jesfion,  the  reduction  in  the  stomach  of 
Jie  food  to  a  nearly  fluid  condition,  is  performed.  The  natural  secretion  of 
that  organ,  the  gastric  juice,  is  said  to  contain  a  very  notable  quantity  of  free 
hydrochloric  acid.  Dilute  hydrochloric  acid,  aided  by  a  temperature  of  98° 
(;iG°-GC)  or  100°  (37°-7C),  dissolves  coagulated  albumin,  fibrin,  &c.  ;  but 
many  hours  are  required  for  that  purpose.  The  gastric  secretion  has  been 
supposed  to  contain  a  peculiar  organic  principle  called  pepsin,  said  to  have 
been  isolated,  to  which  this  power  of  dissolving  albuminous  substances  in 
conjunction  with  the  hydrochloric  acid  is  attributed.  In  the  saliva  a  pecu- 
liar organic  principle  exists,  which  causes  the  conversion  of  starch  into  sugar. 
If  starch  is  held  in  the  mouth  even  for  two  minutes,  this  change  is  found  to 
occur.  The  active  cause  of  this  change  has  been  looked  on  as  a  kind  of  ani- 
mal diastase. 

The  food  of  animals,  or  rather  that  portion  of  the  food  which  is  destined 
to  the  repair  and  renewal  of  the  frame  itself,  is  thus  seen  to  consist  of  sub- 
stances identical  in  composition  with  the  body  it  is  to  nourish,  or  requiring 
but  little  chemical  change  to  become  so. 

The  chemical  phenomena  observed  in  the  animal  system  resemble  so  far 
those  produced  out  of  the  body  by  artificial  means,  that  they  are  all,  or  nearly 
all,  so  far  as  is  known,  changes  in  a  descending  series ;  albumin  and  fibrin 
are  probably  more  complex  compounds  than  gelatin  or  the  membrane  which 
furnishes  it ;  this,  in  turn,  has  a  far  greater  complexity  of  constitution  than 
urea,  the  regular  form  in  which  rejected  azotized  matter  is  conveyed  out  of 
the  body.  Tiie  animal  lives  by  the  assimilation  into  its  own  substance  of  the 
most  complex  and  elaborate  products  of  the  organic  kingdom  ; — products 
which  are,  and,  apparently,  can  only  be,  formed  under  the  influence  of  vege- 
table life. 

The  existence  of  the  plant  is  maintained  in  a  manner  strikingly  dissimilar: 
the  food  supplied  to  vegetables  is  wholly  inorganic ;  the  carbonic  acid  and 
nitrogen  of  the  atmosphere,  the  water  which  falls  as  rain,  or  is  deposited  aa 
dew  ;  the  minute  trace  of  ammoniacal  vapour  present  in  the  air ;  the  alkali 
and  saline  matter  extracted  from  the  soil; — such  are  the  substances  which 
yield  to  plants  the  elements  of  their  growth.  That  green  healthy  vegetables 
do  possess,  under  circumstances  to  be  mentioned  immediately,  the  property 
of  decomposing  carbonic  acid  absorbed  by  their  leaves  from  the  air,  or  con- 
veyed thither  in  solution  through  the  medium  of  their  roots,  is  a  fact  posi- 
tively proved  hj  direct  experiment,  and  rendered  certain  by  considerations 
of  a  very  stringent  kind.  To  eftect  this  very  remarkable  decomposition,  the 
influence  of  light  is  indispensable ;  the  ditfuse  light  of  day  suffices  in  some 
degrees,  but  the  direct  rays  of  the  sun  greatly  exalt  the  activity  of  the  pro- 
cess. The  carbon  separated  in  this  manner  is  retained  in  the  plant  in  union 
with  the  elements  of  water,  with  which  nitrogen  is  also  sometimes  associated, 
while  the  oxygen  is  thrown  ofi"  into  the  air  from  the  leaves  in  a  pure  and 
gaseous  condition. 

The  eS"ect  of  ammoniacal  salts  upon  the  growth  of  plants  is  so  remarkable, 
as  to  leave  little  room  for  doubt  concerning  the  peculiar  function  of  the  am- 
monia recently  discovered  in  the  air.  Plants  which  in  their  cultivated  state 
contain,  and  consequently  require,  a  large  supply  of  nitrogen,  as  wheat,  and 
the  cereals  in  general,  are  found  to  be  greatly  benefited  by  the  application 
to  the  land  of  such  substances  as  putrefied  urine,  which  may  be  looked  upon 
as  a  solution  of  carbonate  of  ammonia,  the  guano'-  of  the  South  Seas,  which 

»  Onano  is  tlie  partially  decomposed  duno;  of  birds,  found  in  immense  quantity  on  some 
of  the  barren  islets  of  the  western  coast  of  South  America,  as  that  of  Teru.  More  recently, 
similar  deposits  have  been  found  on  the  coast  of  Southern  Africa.  The  guano  now  imported 
into  England  from  these  localiiies  is  usually  a  soft,  brown  powder,  of  various  shades  of 
Bolour.     White  specks  of  boue  eavLli,  and  sometimes  masses  of  saline  matter,  may  be  founa 


522  VEGETABLE    NUTRITION.       , 

usually  contains  a  large  proportion  of  ammoniacal  salt,  and  even  of  a  pure 
sulphate  of  ammonia.  Some  of  these  manures  doubtless  owe  a  part  of  their 
value  to  the  phosphates  and  alkaline  salts  they  contain ;  still,  the  chief  efi'ect 
is  certainly  due  to  the  ammonia. 

Upon  the  members  of  the  vegetable  kingdom  thus  devolves  the  duty  of 
building  up,  as  it  were,  out  of  the  inorganic  constituents  of  the  atmosphere, 
— the  carbonic  acid,  the  water,  and  the  ammonia, — the  numerous  complicated 
organic  principles  of  the  perfect  plant,  many  of  which  are  afterwards  des- 
tined to  become  the  food  of  animals,  and  of  man.  The  chemistry  of  vege- 
table life  is  of  a  very  high  and  mysterious  order,  and  the  glimpses  occasion- 
ally obtained  of  its  general  nature  are  few  and  rare.  One  thing,  however, 
is  manifest,  namely,  the  wonderful  relations  between  the  two  orders  of  or- 
ganized beings,  in  virtue  of  which  the  rejected  and  refuse  matter  of  the  one 
is  made  to  constitute  the  essential  and  indispensable  food  of  the  other. 
While  the  animal  lives,  it  exhales  incessantly  from  its  lungs,  and  often  from 
its  skin,  carbonic  acid ;  when  it  dies,  the  soft  parts  of  its  body  undergo  a 
series  of  chemical  changes  of  degradation,  which  terminate  in  the  production 
of  carbonic  acid,  water,  carbonate  of  ammonia,  and,  perhaps,  other  products 
in  small  quantity.  These  are  taken  up  by  a  fresh  generation  of  plants, 
which  may  in  their  turn  serve  for  food  to  another  race  of  animals. 

In  it.  That  which  is  most  recent,  and  prob.ably  most  valuable  as  manure,  often  contains  un- 
decomposed  uric  acid,  besides  much  oxalate  or  bydrochlorate  of  ammonia,  and  alkaline  phos- 
phates, and  other  salts:  it  has  a  most  offensive  odour.  The  specimens  taken  from  oldei 
deposits  have  but  little  smell,  are  darker  in  colour,  contain  no  uric  acid,  and  much  less  am- 
n)oniacal  salt;  the  chief  components  are  bone-earth,  a  peculiar  dark-coloured  organic  matteri 
and  soluble  inorganic  sal  to.    See  also  page  443. 


SUBSTANCES  OBTAINED  FROM  TAR.       523 


SECTION  IX. 

ON    CERTAIN    PRODUCTS    OF  THE   DESTRUCTIVE    DISTILLATION 
AND  SLOW  PUTREFACTIVE  CHANGE  OF  ORGANIC  MATTER. 


SUBSTANCES  OBTAINED  FKOM  TAR. 

There  are  three  principal  varieties  of  tar:  —  (1.)  Tar  of  the  wood-vinegar 
maker,  procured  by  the  destructive  distillation  of  dry  hard  wood;  (2.) 
Stockholm  tar,  so  largely  consumed  in  the  arts,  as  in  ship-building,  &c., 
■which  is  obtained  by  exposing  to  a  kind  of  rude  distillatio  per  descensum  the 
roots  and  useless  parts  of  resinous  pine  and  fir-timb6r;  and,  lastly,  (3.) 
Coal  or  mineral  tar,  a  by-product  in  the  manufacture  of  coal-gas.  This  is 
viscid,  black,  and  ammoniacal. 

All  these  tars  yield  by  distillation,  alone  or  with  water,  oily  liquids  of 
extremely  complicated  nature,  from  which  a  number  of  curious  products,  to 
be  presently  described,  have  been  procured;  the  solid  brown  or  black  resi- 
due constitutes  pitch.     Hard-wood  tar  furnishes  the  following: — 

Paraffin  ;  tar-oil  stearin.  —  This  remarkable  substance  is  found  in 
that  part  of  the  wood-oil  which  is  heavier  than  water;  it  is  extracted  by  re- 
distilling the  oil  in  a  retort,  collecting  apart  the  last  portions,  gradually 
adding  a  quantity  of  alcohol,  and  exposing  the  whole  to  a  low  temperature. 
Thus  obtained,  paraffin  appears  in  the  shape  of  small,  colourless  needles, 
fusible  at  110°  (43°-3C)  to  a  clear  liquid,  which  on  solidifying  becomes 
glassy  and  transparent.  It  is  tasteless  and  inodorous ;  volatile  without 
decomposition;  and  burns,  when  strongly  heated,  with  a  luminous  yet 
smoky  flame.  It  is  quite  insoluble  in  water,  slightly  soluble  in  alcohol, 
freely  in  ether,  and  miscible  in  all  propoi'tions,  when  melted,  with  both  fixed 
and  volatile  oils.  The  most  energetic  chemical  reagents,  as  strong  acids, 
Jilkalis,  chlorine,  &c.,  fail  to  exert  the  smallest  action  on  this  substance;  it 
is  not  known  to  combine  in  a  definite  manner  with  any  other  body,  whence 
its  extraordinary  name,  from  paritm  ajjinis. 

Paraffin  contains  carbon  and  hydrogen  only,  and  in  the  same  proportions 
as  in  olefiant  gas,  or  CH.  M.  Lewy,  of  Copenhagen,  makes  it  CgoHji.  The 
rational  formula  is  unknown. 

EupiONE.' —  This  is  the  chief  component  of  the  light  oil  of  wood-tar;  i* 
occurs  also  in  the  tar  of  animal  matters,  and  in  the  fluid  product  of  the  dis* 
tillation  of  rape-seed  oil.  Its  separation  is  effected  by  the  agency  of  concen- 
trated sulphuric  acid,  or  of  a  mixture  of  sulphuric  acid  and  nitre,  which 
oxidizes  and  destroys  most  of  the  accompanying  substances.  In  a  pure 
state,  it  is  an  exceedingly  thin,  colourless  liquid,  of  agreeable  aromatic 
odour,  but  destitute  of  taste  ;  it  is  the  lightest  known  liquid,  having  a  den- 
sity of  0  655.  At  116°  (46°6C)  it  boils  and  distils  unchanged.  Dropped 
upon  paper,  it  makes  a  greasy  stain,  which  after  a  time  disappears.  Eupione 
is  very  inflammable,  and  burns  with  a  bright  luminous  flame.     In  water  it  is 

•  From  tZ,  gfiod,  Insautiful.  and  itiov,  fat. 


624  SUBSTANCES    OBTAINED    FROM     TAR. 

quite  insoluble,  in  rectified  spirit  nearly  so,  but  with  ether  and  oils  freely 
miscible. 

Eupione  is  a  hydrocarbon  ;  according  to  M.  Hess  it  consists  of  CglTg.  It 
is  very  probable  that  eupione  frequently  contains  and  sometimes  entirely 
consists  of  hydride  of  amyl  (see  page  389). 

Other  volatile  oils,  having  a  similar  origin,  and  perhaps  a  similar  compo- 
sition, but  differing  from  the  above  in  specific  gravity  and  boiling-point,  are 
sometimes  confounded  with  eupione.  The  study  of  these  substances  presents  ' 
many  serions  difl[iculties.  It  is  even  doubtful  whether  the  eupione  be  not 
formed  by  the  energetic  chemical  agents  employed  in  its  sitpposed  purifica- 
tion, and  this  remark  applies  with  even  greater  force  to  the  next  three  or 
four  tar-products  to  be  noticed. 

PiCAMAR.' — A  component  of  the  heavy  oil  of  wood  ;  it  is  a  viscid,  colour- 
less, oily  liquid,  of  feeble  odour,  but  intensely  bitter  taste.  Its  density  is 
1-095,  and  it  boils  at  518°  (270°C).  It  is  insoluble  in  water,  but  dissolves 
in  all  proportions  in  alcohol,  ether,  and  the  oils.  The  most  characteristic 
property  of  picamar  is  that  of  forming  with  the  alkalis  and  ammonia  crys- 
talline compounds,  which,  although  decomposed  by  water,  are  soluble  with- 
out change  in  spirit.     The  composition  of  this  substance  is  unknown. 

Kapnomor.'' —  Such  is  the  name  given  by  Dr.  Reichenbach  to  another  oily 
liquid  obtained  from  the  same  source  as  the  last,  by  a  long  and  complex 
process,  in  which  strong  solutions  of  caustic  potassa  are  freely  used.  It  is 
described  as  a  colourless  volatile  oil,  of  high  boiling-point,  and  rather  lighter 
than  water;  it  has  an  odour  of  ginger,  and  a  taste  feeble  at  first,  but  after- 
wards becoming  connected  with  an  insupportable  sense  of  sufi'ocation. 
Water  refuses  to  dissolve  it;  alcohol  and  ether  take  it  up  easily;  and  oil 
of  vitriol  combines  with  it,  giving  rise  to  a  complex  acid,  the  potassa-salt  of 
Wliich  is  crystallizable.     Its  composition  is  unknown. 

CEnKiRRT.' —  The  lighter  oil  of  hard-wood  tar  contains  a  substance,  separ- 
able from  the  eupione,  &c.,  by  caustic  alkalis,  which  in  contact  with  oxidizing 
agents,  as  sulphate  of  sesquioxide  of  iron,  chromic  acid,  or  even  atmos- 
pheric air,  yields  a  mass  of  small,  red,  reticulated  crystals,  infusible  by 
heat,  and  soluble  in  concentrated  sulphuric  acid  with  deep  indigo-blue 
colour.  This  substance  is  insoluble  in  water,  alcohol,  and  ether ;  nothing  is 
known  respecting  its  composition. 

Kreosotk.*  —  This  is  by  far  the  most  important  and  interesting  body  of 
the  group ;  its  discovery  is  due  to  Dr.  Reichenbach  ;  it  is  the  principle  to 
which  wood-smoke  owes  its  power  of  curing  and  preserving  salted  meat  and 
other  provisions.  Kreosote  is  most  abundantly  contained  in  the  heavy  oil 
of  beech-tar,  as  procured  from  the  wood-vinegar  maker,  and  is  thence  ex- 
tracted by  a  most  tedious  and  complicated  series  of  operations ;  it  certainly 
pre-exists,  however,  in  the  original  material.  The  tar  is  distilled  in  a  me- 
tallic vessel,  and  the  ditt'erent  products  collected  apart ;  the  most  volatile 
portion,  which  is  lighter  than  water,  and  consists  chiefly  of  eupione,  is  re- 
jected ;  the  second  portion  is  denser,  and  contains  the  kreosote,  and  is  set 
aside;  the  distillation  is  stopped  when  paraffin  begins  to  pass  over  in  quan- 
tity. The  impure  kreosote  is  first  agitated  with  carbonate  of  potassa  to 
remove  adliering  acid,  separated,  and  re-distilled,  the  first  part  being  again 
rejected;  it  is  next  strongly  shaken  with  a  solution  of  phosphoric -acid,  and 
again  distilled ;  a  quantity  of  ammonia  is  thus  separated.  Afterwards,  it  is 
dissolved  in  a  solution  of  caustic  potassa  of  specific  gravity  1-12,  and  de- 

'  From  pix,  and  amm'us,  in  allusion  to  its  bitter  taste. 

*  From  KUiiVdi,  smoke,  ftoipa,  pan. 

'  From  cixlrium,  the-  old  name  for  acid  tar-water,  and  rete,  a  net. 

*  Derived  from  Kpfai,  tiesb,  and  ffuJ^w,  I  preserve. 


SUBSTANCES  OBTAINED  FROM  TAR.      525 

canted  from  the  insoluble  oil  which  floats  on  the  surface ;  this  alkaline  liquid 
is  boiled,  and  left  some  time  in  contact  with  air,  by  which  it  acquires  a  brown 
colour  from  the  oxidation  of  some  yet  unknown  substance  present  in  the 
crude  product.  The  compound  of  kreosote  and  alkali  is  next  decomposed 
by  sulphuric  acid :  the  separated  kreosote  is  again  dissolved  in  caustic 
potassa,  boiled  in  the  air,  and  the  solution  decomposed  by  acid,  and  this 
treatment  repeated  until  the  product  ceases  to  become  coloured  by  the  joint 
influence  of  oxygen  and  the  alkaline  base.  When  so  far  purified,  it  is  well 
washed  with  water,  and  distilled.  The  first  portion  contains  water;  that 
which  succeeds  is  pure  kreosote. 

In  this  condition  kreosote  is  a  colourless,  somewhat  viscid  oily  liquid,  of 
great  refractive  and  dispersive  power.  It  is  quite  neutral  to  test-paper ;  it 
has  a  penetrating  and  most  peculiar  odour,  that,  namely,  of  smoked  meat, 
and  a  pungent  and  almost  insupportable  taste  when  placed  in  a  very  small 
quantity  upon  the  tongue.  The  density  of  this  substance  is  1-037,  and  its 
boiling-point  397°  (202° -SC).  It  inflames  with  difficulty,  and  then  burns 
with  a  smoky  light.  When  quite  pure,  it  is  inalterable  by  exposure  to  the 
air ;  much  of  the  kreosote  of  commerce  becomes,  however,  under  these  cir- 
cumstances, gradually  brown.  100  parts  of  cold  water  take  up  about  IJ 
parts  of  kreosote ;  at  a  high  temperature  rather  more  is  dissolved,  and  the 
hot  solution  abandons  a  portion  on  cooling.  The  kreosote  itself  absorbs 
water  also  to  a  considerable  extent.  In  acetic  acid  it  dissolves  in  much 
larger  quantity.  Alcohol  and  ether  mix  with  kreosote  in  all  proportions. 
Concentrated  sulphuric  acid,  by  the  aid  of  heat,  blackens  and  destroys  it. 
Caustic  potassa  dissolves  kreosote  with  great  facility,  and  forms  with  it  a 
definite  compound,  which  crystallizes  in  brilliant  pearly  scales. 

Kreosote  consists  of  carbon,  hydrogen,  and  oxygen,  but  its  exact  compo- 
sition is  yet  uncertain.     The  formula  C,4Hg02  has  been  given. 

The  most  remarkable  and  characteristic  feature  of  the  compound  in  ques- 
tion is  its  extraordinary  antiseptic  power.  A  piece  of  animal  flesh  steeped 
in  a  very  dilute  solution  of  kreosote  dries  up  to  a  mummy-like  substance, 
but  absolutely  refuses  to  putrefy.  The  well-known  efficacy  of  impure  wood- 
vinegar  in  preserving  provisions  is  with  justice  attributed  to  the  kreosote  it 
contains ;  and  the  effect  of  mere  wood-smoke  is  also  thus  explained.  In  a 
pure  state,  kreosote  is  sometimes  employed  by  the  dentist  for  relieving  tooth- 
ache arising  from  putrefactive  decay  in  the  substance  of  the  tooth. 

Chrysen  and  pyren.  —  M,  Laurent  extracted  from  pitch,  by  distillation 
at  a  high  temperature,  two  new  solid  bodies,  to  which  he  gave  the  preceding 
names ;  they  condense  together,  with  a  quantity  of  oily  matter,  partly  in  the 
necK  of  the  retort,  and  partly  in  the  receiver,  and  are  separated  by  the  aid 
of  ether.  Chrysen,  so  called  from  its  golden  colour,  is  a  pure  yellow,  crystal- 
line powder,  which  fuses  by  heat,  and  sublimes  without  much  decomposition. 
It  is  insoluble  in  water  and  alcohol,  and  nearly  insoluble  in  ether:  warm  oil 
of  vitriol  dissolves  it,  with  the  development  of  a  beautiful  deep-green  colour. 
Boiling  nitric  acid  converts  it  into  an  insoluble  red  substance,  which  has  not 
been  studied.     Chrysen  is  composed  of  CgH. 

Fyrm  differs  from  the  preceding  substance  in  being  colourless,  crystal- 
lizing in  small,  soft,  micaceous  scales,  soluble  in  boiling  alcohol  and  ether. 
It  is  fusible  and  volatile.     Pyren  contains  C5H2. 

Oil  of  ordinary  tar,  obtained  by  distillation  alone,  or  with  water,  consists 
in  great  measure  of  unaltered  oil  of  turpentin,  mixed,  however,  with  em- 
pyreumatic  oily  products,  which  give  it  a  powerful  odour  and  a  dark  colour 
The  residual  pitch  contains  much  pine-resin,  and  thus  differs  from  the  solid 
portion  of  the  hard  wood-tar  so  frequently  mentioned. 


626  VOLATILE    PRINCIPLES     OP    COAL-TAR. 

Volatile  Principles  of  Coal- Tar. 

Co.al-tar  yields  on  distillation  a  large  quantity  of  thin,  dark-c«Ioured, 
volatile  oil,  which,  when  agitated  with  dilute  sulphuric  acid  to  remove  am- 
monia, and  twice  rectified  with  water,  becomes  nearly  colourless :  it  is  very 
volatile,  lighter  than  water,  very  inflammable,  and  possesses  in  a  high  degree 
the  property  of  dissolving  caoutchouc,  on  which  account  it  is  vei*y  exten- 
sively used  in  the  manufacture  of  water-proof  fabrics  containing  that 
material. 

This  coal-oil  is  a  mixture  of  a  great  variety  of  liquids  and  solids  dissolved 
in  the  oil.  By  the  action  of  acids  and  alkalis,  this  mixture  may  be  conve- 
niently divided  into  three  separate  groups.  (1)  A  group  of  basic  compounds 
soluble  in  acids;  (2)  an  acid  portion  soluble  in  alkalis;  and  (3)  a  group  of 
neutral  constituents. 

The  basic  constituents  form  but  a  small  part  of  coal-tar-oil.  They  are  ex- 
tracted by  agitating  successively  large  quantities  of  the  oil  with  hydrochloric 
acid,  and  afterwards  distilling  the  acid  watery  liquid  obtained  with  excess 
of  hydrate  of  lime.  The  bases  thus  obtained  consist  chiefly  of  picoline  (see 
page  465),  aniline  (see  page  459),  and  leucoline  (see  page  464),  and  are 
separated  by  distillation ;  these  three  compounds  boiling  at  very  different 
temperatures. 

The  acid  portion  of  coal-tar-oil  consists  essentially  of  carbolic  acid  or 
phenol. 

Carbolic  acid  ;  phenol. — Common  coal-tar-oil  is  agitated  with  a  mixture 
of  hydrate  of  lime  and  water,  the  whole  being  left  for  a  considerable  time ; 
the  aqueous  liquid  is  then  separated  from  the  undissolved  oil,  deconiposed 
by  hydrochloric  acid,  and  the  oily  product  obtained  purified  by  cautious  dis- 
tillation, the  first  third  only  being  collected.  Or  crude  coal-oil  is  subjected 
to  distillation  in  a  retort  furnished  with  a  thermometer,  and  the  portion 
which  passes  over  between  the  temperatures  of  300° — 400°  (149° — 204°-5C) 
collected  apart.  This  product  is  then  mixed  with  a  hot  strong  solution  of 
caustic  potassa,  and  left  to  stand ;  a  whitish,  somewhat  crystalline,  pasty 
mass  is  obtained,  which  by  the  action  of  water  is  resolved  into  a  light  oily 
liquid  and  a  dense  alkaline  solution.  The  latter  is  withdrawn  by  a  syphon, 
decomposed  by  hydrochloric  acid,  and  the  separated  oil  purified  by  contact 
with  chloride  of  calcium  and  re-distillation.  Lastly,  it  is  exposed  to  a  low 
temperature,  and  the  crystals  formed  drained  from  the  mother-liquor  and 
carefully  preserved  from  the  air. 

Pure  carbolic  acid  forms  long  colourless  prismatic  needles,  which  melt  at 
95°  (35°C)  to  an  oily  liquid,  boiling  at  370°  (180°C),  and  greatly  resembling 
kreosote'  in  many  particulars,  having  a  very  penetrating  odour  and  burning 
taste,  and  attacking  the  skin  of  the  lips.  Its  sp.  gr.  is  1-065.  It  is  slightly 
soluble  in  water,  freely  in  alcohol  and  ether,  and  has  no  acid  reaction  to 
test-paper.  The  crystals  absorb  moisture  with  avidity,  and  liquefy.  It  co- 
agulates albumin.  Sulphur  and  iodine  dissolve  in  it;  nitric  acid,  chlorine, 
and  bromine  attack  it  with  energy.     Carbolic  acid  contains  CigHjO,!^. 

In  its  chemical  deportment  carbolic  acid  stands  very  near  the  alcohols,  a 
fact  to  which  allusion  has  been  made  already  in  former  sections  (see  pages 
399  and  401) ;  we  may  assume  in  it  a  compound  radical,  phenyl,  CijHgrrsPyl, 
analogous  to  ethyl,  when  carbolic  acid  becomes  Pyl  0,110,  or  hydrated  oxide 
wf  phenyl. 

With  sulphuric  acid,  hydrate  of  oxide  of  phenyl  forms  the  compound  acid, 
mlpliaphenic  acid,  Ci2H50,2S05,nO=Pyl  0,2S03,HO,  which  assumes  a  syrupy 

A  gre.at  de.il  of  the  kreosote  which  occurs  in  commerce  is,  in  fact,  nothiug  but  moi'e  or 
loss  pure  carbohc  acid. 


VOLATILE    PRINCIPLES    OF    COAL-TAR. 


527 


state  in  the  dry  vacuum.  This  acid  closely  corresponds  to  sulphovinic  acid 
(see  page  o58).  The  baryta-salt  crystallizes  from  alcohol  in  minute  needles. 
Phonyl-alcohol  dissolves  potassium  with  evolution  of  hydrogen,  a  com- 
pound OialljOjKO  being  produced,  which  is  analogous  to  the  substance  formed 
in  a  similar  manner  from  common  alcohol  (see  page  347).  On  heating  this 
potassa-compound  Avith  iodide  of  methyl,  ethjd,  or  amyl,  a  series  of  double 
ethers  are  produced  represented  by  the  following  formulae : — 

Oxide  of  phenyl  and  methyl PylO,MeO  =   C,2n50,C2H30    =  CiJI^Oj 

Oxide  of  phenyl  and  ethyl  PylOjAeO    =   Ci2H50,C4H30    =  C,6H,(,0j 

Oxide  of  phenyl  and  amyl  Pyl0,Ay0    =   CiglWCjoHiiO  =  CaallieOg 

Those  substances  also  described  by  the  names  aniiol  (because  it  is  likewise 
produced  by  th«}  distillation  of  anisic  acid  (see  page  491),  phenelol  and  phe- 
namylol  are  evidently  analogous  to  the  compounds  of  oxide  of  methyl  with 
those  of  ethyl  and  amyl,  which  have  been  mentioned  in  pages  382  and  389. 

A  chloride  of  phenyl,  CigHgClrrzPylCl,  has  been  produced  by  the  action  of 
pentachloride  of  phosphorus  upon  hydrated  oxide  of  phenyl.  This  com- 
pound, however,  which  is  a  heavy  oil,  is  but  very  imperfectly  known. 

Cyanide  of  phenyl,  C,4H5N=C,2ll5C2N=PylCy,  has  not  yet  been  produced 
from  phenyl-alcohol  directly.  The  substance,  however,  which  has  been  de- 
scribed under  the  name  of  benzonitrile  (page  401),  is  both  by  composition 
and  deportment  cyanide  of  phenyl,  perfectly  analogous  to  cyanide  of  ethyl 
(see  page  354).  Boiled  with  potassa  it  is  converted  into  ammonia  and  ben- 
zoic acid,  cyanide  of  ethyl  furnishing  ammonia  and  propionic  acid.  Starting 
from  this  decomposition,  benzoic  acid  may  be  viewed  as  phenyl-oxalic  acid 
^i4^^5^3'HO=Ci2H5,C203,HO,  just  as  propionic  acid  may  be  regarded  as 
ethyl-oxalic  acid  (see  page  392). 

Hydrated  oxide  of  phenyl  when  treated  with  chloride  of  benzoyl  (see  page 
400)  yields  hydrochloric  acid  and  a  white  fusible  crystalline  compound  which 
is  benzoaie  of  phenyl  €521150,0,411503= PylO,BzO,  analogous  to  benzoate  of 
ethyl;  when  heated  with  ammonia,  phenyl-alcohol  yields  aniline  G ^2^1^'^ z=z 
CjallsHgN^PylHgN  {phenylamine),  the  ethylamine  of  the  phenyl-series  (see 
page  4o9). 

The  following  table  gives  a  synopstis  of  the  phenyl-compounds,  which  have 
been  placed  iu  juxtaposition  with  the  corresponding  terms  of  the  ethyl- 
series  : — 

Phenyl-alcohol           PylO,HO  AeO,HO  Ethyl-alcohol 

^""potassl  ^^^"^^"}^^^^'^^  AeO,KO  Oxide  of  ethyl-potassa 

Sulphophenic  acid     PylO,2S03,HO  AeO,2S03,HO     Sulphovinic  acid 

AeO  Oxide  of  ethyl 

Chloride  of  phenyl     PylCl(?)  Aecl  Chloride  of  ethyl 

Cyanide  of  phenyl  |  p  ,p                         ^  f  Cyanide  of  ethyl  (pro- 

(benzonitrile)       /^  •>'''- J^  ^^^J  \      pio  nitrile) 

Benzoate  of  phenyl     PylOjPylCjOa  AeO,Ae,C203  Propionate  of  ethyl 

Phenyl-amine  (aui- 1  x^rr -n  1  attt  *  t-.xu   ^ 

jj^^  ^         vlSrigPyl  NIT^Ae  Ethylamine 

Phenyl-urea  C2(n3Pyl)N02      C2(H3Ae)N02      Ethyl-urea. 

Chlorophenisic  acid.  —  This  is  the  characteristic  and  principal  product  of 
the  action  of  chlorine  on  hydrate  of  oxide  of  phenyl.  The  pure  substance 
is  not  necessary  for  the  preparation  of  this  body,  those  portions  of  crude 
coal-oil  which  boil  between  360° — 400°  (182°-2 — 204°-oC)  answering  verjr 
well.  The  oil  is  saturated  with  chlorine,  and  distilled  in  the  open  air,  the 
first  and  last  portions  being  rejected;  the  product  is  again  treated  witL 


528     VOLATILE  PRINCIPLES  OP  COAL-TAR. 

chlorine  until  the  whole  solidifies.  The  crystals  are  drained  and  dissolved 
in  hot  dilute  solution  of  ammonia ;  on  cooling,  the  sparingly  soluble  chloro- 
phenisate  of  ammonia  crystallizes  out.  This  is  dissolved  in  pure  water,  de- 
composed by  hydrochloric  acid,  washed,  and,  lastly,  distilled. 

Chlorophenisic  acid  forms  exceedingly  fine,  colourless,  silky  needles,  which 
melt  when  gently  heated ;  it  has  a  very  penetrating,  persistent,  and  charac- 
teristic odour,  is  very  sparingly  soluble  in  water,  but  dissolves  freely  in 
alcohol,  ether,  and  hot  concentrated  sulphuric  acid.  It  slowly  sublimes  at 
common  temperatures,  and  distils  with  ebullition  when  strongly  heated. 
Chlorophenisic  acid  forms  well-defined  salts,  and  contains  C,2(li2C]3)0,lIO. 
By  the  action  of  a  great  excess  of  chlorine  an  analogous  acid  richer  in  chlo- 
rine is  formed.  It  is  called  chlorophcnusic  acid,  and  contains  CjjClgOjHO. 
Brornophenisic  acid  is  prepared  by  analogous  means,  and  possesses  a  consti- 
tution and  character  greatly  resembling  those  of  the  chlorine-compound. 

Nitrophenasic  acid.  —  On  distilling  phenyl-alcohol  with  very  dilute  nitric 
acid,  beautiful  yellow  needles  are  obtained,  soluble  in  ammonia  and  potassa, 
and  yielding  a  beautiful  red  silver-salt.  This  substance  is  nitrophenasic  acid, 
Ci2H4N06,HO  =  Cj2(H4N04)0,HO.  Nitrophencsic  and  nitrophenisic  acids  may 
be  prepared  directly  from  the  oil  which  is  employed  in  the  preparation  of 
chlorophenisic  acid.  The  oil  is  carefully  mixed  in  a  large  open  vessel  with 
rather  more  than  its  own  weight  of  ordinary  nitric  acid.  The  action  is  very 
violent.  The  brownish-red  substance  produced  is  slightly  washed  with 
water,  then  boiled  with  dilute  ammonia,  and  filtered  hot.  A  brown  mass 
remains  on  the  filter,  which  is  preserved  to  prepare  nitrophenisic  acid,  and 
the  solution  deposits  on  cooling  a  very  impure  ammoniacal  salt  of  nitro- 
phenesic  acid,  which  requires  several  successive  crystallizations,  after  which 
it  is  decomposed  by  nitric  acid  and  the  product  crystallized  from  alcohol. 

Nitrophencsic  acid  forms  blonde-coloured  prismatic  crystals,  very  spar- 
ingly soluble  even  in  boiling  water,  but  freely  soluble  in  alcohol.  It  has  no 
odour.  Its  taste,  at  first  feeble,  becomes  after  a  short  time  very  bitter.  At 
219°  (104°C)  it  melts,  and  on  cooling  crystallizes.  In  very  small  quantity 
it  may  be  distilled  without  decomposition,  but  when  briskly  heated  it  often 
detonates,  but  not  violently.  The  salts  of  this  acid  are  yellow  or  orange 
and  very  beautiful :  they  are  mostly  soluble  in  water,  and  detonate  feebly 
when  heated.  The  acid  contains  Ci2H3N209,HO=C,2H3(N04)20,HO.  Nitro- 
phenisic acid  is  identical  with  picric  or  carbazotic  acid  (see  page  473).  It 
may  be  prepared  with  great  economy  from  impure  nitrophencsic  acid,  or 
from  the  brown  mass  insoluble  in  dilute  ammonia  already  referred  to.  It  is 
purified  by  a  process  similar  to  that  employed  in  the  case  of  the  preceding 
substances.    Nitrophenisic  acid  contains  C,2H2N30i3,HO=Ci2H2(N04)30,HO.' 

The  following  table  exhibits  the  relation  of  these  substitution-products; — 

Phenyl-alcohol  CjaHg  0,H0  =  Phenol 

I  Chlorophenisic  acid  0,2(112013)  0,H0  =  Trichlorophenol 

Nitrophenasic  acid    C,2(Il4N04)        0,HO  =  Nitrophenol 
Nitrophencsic  acid   C,2(H3[N04]2)  0,HO  =  Binitrophenor  - 
Nitrophenisic  acid    C,2(H2[N04]3)  0,HO  =  Trinitrophenol. 

The  neutral  portion  of  coal-tar  naphtha  consists  of  a  great  variety  of  hy- 
drocarbons, partly  liquid,  partly  solid.  The  liquid  hydrocarbons  have  been 
already  described  (see  pages  398  and  408).  They  are  chiefly  benzol,  toluol, 
xylol,  cumol,  and  cymol.''  The  solid  hydrocarbons  are  naphthalin  and  para- 
naphthalin  together  with  several  similar  substances  less  perfectly  known. 

*  Ann.  Chim.  et  Phys.  3d  scries,  iii.  195. 

'  The  same  hydrocarbons  have  been  lately  found  by  M.  Cahours  in  the  oily  liquids  pre 
ripitated  by  water  from  commercial  wood-ppirits  (^see  page  387). 


VOLATILE    PRINCIPLES    OP    COAL-TAR.  529 

Naphthalin. — When,  in  the  distillation  of  coal-tar,  the  last  portion  of 
the  volatile  oily  product  is  collected  apart  and  left  to  stand,  a  quantity  of 
solid,  crystalline  matter  separates,  which  is  principally  composed  of  the 
substance  in  question.  An  additional  quantity  may  be  obtained  by  pushing 
the  distillation  until  the  contents  of  the  vessel  begin  to  char ;  the  naphthalin 
then  condenses  in  the  solid  state,  but  dark-coloured  and  very  impure.  By 
simple  sublimation,  once  or  twice  repeated,  it  is  obtained  perfectly  white. 
In  this  state  naphthalin  forms  large,  colourless,  transparent,  brilliant,  crys- 
talline plates,  exhaling  a  faint  and  peculiar  odour,  which  has  been  compared 
to  that  of  the  narcissus.  Naphthalin  melts  at  176°  (80°C)  to  a  clear,  colour- 
less liquid,  which  crystallizes  on  cooling;  it  boils  at  413°  (211°-6C),  and 
evolves  a  vapour  whose  density  is  4-528.  When  strongly  heated  in  the  air, 
it  inflames  and  burns  with  a  red  and  very  smoky  light.  It  is  insoluble  in 
cold  water,  but  soluble  to  a  slight  degree  at  the  boiling  temperature  ;  alcohol 
and  ether  dissolve  it  easily ;  a  hot  saturated  alcoholic  solution  deposits  fine 
iridescent  crystals  on  cooling. 

Naphthalin  is  found  by  analysis  to  contain  CyjH^  or  C^q^^. 

Naphthalin  dissolves  in  warm  concentrated  sulphuric  acid,  forming  a  red 
liquid,  which,  when  diluted  with  water,  and  saturated  with  carbonate  of 
baryta,  yields  salts  of  at  least  two  distinct  acids,  analogous  to  sulphovinio 
acid.  One  of  these,  the  sulphonaphthalic  acid  of  Mr.  Faraday,  crystallizes 
from  a  hot  aqueous  solution  in  small  white  scales,  which  are  but  sparingly 
soluble  in  the  acid.  The  free  acid  is  obtained  in  the  usual  manner  by  de- 
composing the  baryta-salt  with  sulphuric  acid ;  it  forms  a  colourless,  crys- 
talline, brittle  mass,  of  acid,  metallic  taste,  very  deliquescent,  and  very  solu- 
ble in  water.  The  second  baryta-salt  is  still  less  soluble  than  the  preceding. 
The  composition  of  sulphonaphthalic  acid  is  C2oH7S205,HO. 

Fuming  nitric  acid  at  a  high  temperature  attacks  naphthalin  ;  the  products 
are  numerous,  and  have  been  attentively  studied  by  M.  Laurent.  The  same 
chemist  has  described  a  long  series  of  curious  products  of  the  action  of  chlo- 
rine on  naphthalin.  Nitric  acid  gives  rise  to  a  great  number  of  nitro-sub- 
stitutes,  the  most  interesting  of  which,  is  the  compound  known  by  the  name 
nitronaphthalase,  which,  when  submitted  to  Zinin's  process,  is  converted  into 
naphthalidine  (see  page  462).  Among  the  derivatives  of  naphthalin,  a  com- 
pound deserves  to  be  mentioned,  which  has  been  described  under  the  name 
of  phthalic  acid.  This  acid  has  not  yet  been  produced  directly  from  naphtha- 
lin, but  may  be  obtained  by  boiling  one  of  the  products  of  the  action  of  chlo- 
rine upon  naphthalin,  namely,  the  tetrachloride  of  naphthalin  (C20H8CI4) 
with  nitric  acid.  The  same  substance  is  formed  by  submitting  alizarin  to  the 
action  of  nitric  acid. 

Phthalic  acid  crystallizes  in  yellow  plates  ;  it  is  but  slightly  soluble  in  cold 
water,  but  dissolves  freely  in  alcohol  and  ether.  Phthalic  acid  is  bibasic,  and 
contains  CjgH40g,2HO;  when  heated  it  loses  2  eq.  of  water,  and  becomes 
Ci6^4^6*  Treated  with  fuming  nitric  acid  it  yields  a  nitro-acid,  nitro-phtha- 
lic  acid,  Ci6(H3N04)  Og,  2H0.  When  distilled  with  baryta  it  is  converted  into 
benzol : — 

C,6^l608-f4BaO  =  4(BaOCOj)-fC,2H8 

Phthalic  acid.  Benzol. 

The  formation  of  phthalic  acid  from  alizarin  has  established  a  most  inte- 
resting connection  between  the  naphthalin  and  alizarin-series.  It  would  be 
of  great  interest  if  naphthalin,  which  is  produced  ^n  enormous  quantities  in 
the  manufacture  of  coal-gas,  but  has  not  yet  found  any  useful  application, 
could  be  converted  by  chemical  processes  into  alizarin.  That  there  is  a  hope 
of  such  a  conversion  being  possible,  is  even  now  pointed  out  by  the  close 
45 


530  PETROLEUM,    NAPHTHA., 

analogy  J»f  one  of  the  chlorine  products  of  naphthalin,  of  chloronaphthalu 
acid,  both  in  composition  and  properties  with  alizarin.  This  substance  con- 
tains C2o(H5Cl)06,  and  may  be  viewed  as  chloralizarin : — 

Alizarin Cgg  Hg      Og 

Cloronaphthalic  acid C2o(H5Cl)08. 

Chloronaphthalic  acid  produces  most  beautifully  coloured  compounds  with 
the  metallic  oxides. 

The  history  of  the  formation  of  naphthalin  is  rather  interesting ;  it  is  per- 
haps the  most  stable  of  all  the  more  complex  compounds  of  carbon  and  hydro- 
gen :  in  a  vessel  void  of  free  oxygen  it  may  be  heated  to  any  extent  without 
decomposition ;  and.  indeed,  where  other  carburets  of  hydrogen  are  exposed 
to  a  very  high  temperature,  as  by  passing  in  vapour  through  a  red-hot 
porcelain  tube,  a  certain  quantity  of  naphthalin  is  almost  invariably  pro- 
duced. Hence  its  presence  in  coal  and  other  tar  is  mainly  dependent  upon 
the  temperature  at  which  the  destructive  distillation  of  the  organic  substance 
has  been  conducted.  Lampblack  very  frequently  contains  naphthalin  thus 
accidentally  produced. 

Paranaphthalin. — This  substance  occurs  in  the  naphthalin  of  coal-tar, 
and  is  separated  by  the  use  of  alcohol,  in  which  ordinary  naphthalin  is  freely 
soluble,  whilst  paranaphthalin  is  almost  totally  insoluble  ;  in  other  respects 
it  much  resembles  naphthalin.  The  crystals  obtained  by  sublimation  ai'c, 
however,  usually  smaller  and  less  distinct.  It  melts  at  356°  (180°C),  and 
boils  at  570°  (299°C),  or  above.  Its  best  solvent  is  oil  of  turpentin.  Para- 
naphthalin has  the  same  composition  as  naphthalin  itself;  the  density  of  its 
vapour  is,  however,  different,  viz.,  6-741.  Its  composition  may  be  repre- 
sented by  the  formula  CgQHjj. 

PETROLEUM,  NAPHTHA,  AND  OTHEK  ALLIED  SUBSTANCES. 

Pit-coal,  lignite  or  hrotcn  coal,  jet,  bitumen  of  various  "km^s,  petroleum  or 
rcck-oil,  and  naphtha,  and  a  few  other  allied  substances  more  rarely  met  with, 
are  looked  upon  as  products  of  the  decomposition  of  organic  matter,  espe- 
cially vegetable  matter,  beneath  the  surface  of  the  earth,  in  situations  where 
the  conditions  of  contact  with  water,  and  nearly  total  exclusion  of  atmo- 
epheric  air,  are  fulfilled.  Deposited  at  the  bottom  of  seas,  lakes,  or  rivers, 
and  subsequently  covered  up  by  accumulations  of  clay  and  sand,  hereafter 
destined  to  become  shale  and  gritstone,  the  organic  tissue  undergoes  a  kind 
of  fermentation,  by  which  the  bodies  in  question,  or  certain  of  them,  are 
slowly  produced.  Carbonic  acid  and  light  carbonetted  hydrogen  are  by-pro- 
ducts of  the  reaction  ;  hence  their  frequent  disengagement,  the  first  from 
beds  of  lignite,  and  the  second  from  the  farther  advanced  and  more  perfect 
coal. 

The  vegetable  origin  of  coal  has  been  placed  beyond  doubt  by  microscopic 
research ;  vegetable  structure  can  be  thus  detected  even  in  the  most  mas- 
sive and  perfect  varieties  of  coal  when  cut  into  thin  slices.  In  coal  of  infe- 
rior quality,  much  mixed  with  earthy  matter,  it  is  evident  to  the  eye;  the 
leaves  of  ferns,  reeds,  and  other  succulent  plants,  more  or  less  resembling 
those  of  the  tropics,  are  found  in  a  compressed  state  between  the  layers  of 
shale  or  slaty  clay,  preserved  in  the  most  beautiful  manner,  but  entirely 
converted  into  bituminous  coal.  The  coal-mines  of  Europe,  and  particularly 
those  of  our  own  country,  furnish  an  almost  complete  fossil-flora ;  a  history 
Df  many  of  the  now  lost  species  which  ouce  decorated  the  surface  of  the 
earth. 

In  the  lignites  the  woody  structure  is  much  more  obvious.  Beds  of  this 
material  are  found  in  very  many  of  the  newer  strata,  above  the  true  coal,  to 
which  they  are  consequently  posterior.     As  an  article  of  fuel,  brown-coal  is 


AND    OTHER    ALLIED    SUBSTANCES.  531 

cf  comparatively  small  value ;  it  resembles  peat,  giving  but  little  flame  and 
^mitting  a  disagreeable,  pungent  smell. 

Jet,  used  for  making  black  ornaments,  is  a  variety  of  lignite. 

The  true  bitumens  are  destitute  of  all  organic  structure;  they  appear  to 
have  arisen  from  coal  or  lignite  by  the  action  of  subterranean  heat,  and 
very  closely  resemble  some  of  the  products  yielded  by  the  destructive  dis- 
tillation of  those  bodies.  They  are  very  numerous,  and  have  yet  been  but 
imperfectly  studied. 

1.  Mineral  pitch,  or  compact  bitumen,  the  asphaltum  or  Jew^s  pitch  of  some 
authors.  —  This  substance  occurs  abundantly  in  many  parts  of  the  w^orld ; 
as,  in  the  neighbourhood  of  the  Dead  Sea  in  Judea ;  in  Trinidad,  in  the 
famous  pitch  lake,  and  elsewhere.  It  generally  resembles  in  aspect  common 
pitch,  being  a  little  heavier  than  water,  easily  melted,  very  inflammable,  and 
burning  with  a  red,  smoky  flame.  It  consists  principally  of  a  substance 
called  by  M.  Boussingault  asphaltene,  composed  of  Cj^HigOg.  It  is  worthy 
of  remark,  that  M.  Laurent  found  paranaphthalin  in  a  native  mineral 
pitch. 

2.  Mineral  tar  seems  to  be  essentially  a  solution  of  asphaltene  in  an  oily 
fluid  called  petrolene.  This  has  a  pale  yellow  colour  and  peculiar  odour ;  it 
is  lighter  than  water,  very  combustible,  and  has  a  high  boiling  point.  It 
has  the  same  composition  as  the  oils  of  turpentin  and  lemon-peel,  namely 
CioHg.  Asphaltene  contains,  consequently,  the  elements  of  petrolene,  to- 
gether with  a  quantity  of  oxygen,  and  probably  arises  from  the  oxidation  of 
that  substance. 

3.  Elastic  bitumen ;  mineral  caoutchouc.  —  This  curious  substance  has  only 
been  found  in  three  places  ;  in  a  lead-mine  at  Castleton,  in  Derbyshire ;  at 
Montrelais,  in  France ;  and  in  the  State  of  Massachusetts.  In  the  two  latter 
localities  it  occurs  in  the  coal-series.  It  is  fusible,  and  resembles  in  many 
respects  the  other  bitumens. 

Under  the  names  petroleum  and  naphtha  are  arranged  various  mineral  oils 
which  are  observed  in  many  places  to  issue  from  the  earth,  often  in  con- 
siderable abundance.  There  is  every  reason  to  suppose  that  these  owe  their 
origin  to  the  action  of  internal  heat  upon  beds  of  coal,  as  they  are  usually 
found  in  connection  with  such.  The  term  naphtha  is  given  to  the  thinner 
and  purer  varieties  of  rock-oil,  which  are  sometimes  nearly  colourless ;  the 
darker  and  more  viscid  liquids  bear  the  name  of  petroleum. 

Some  of  the  most  noted  localities  of  these  substances  are  the  following: — 
The  north-west  side  of  the  Caspian  Sea,  near  Baku,  where  beds  of  marl  are 
found  saturated  with  naphtha.  Wells  are  sunk  to  the  depth  of  about  30 
feet,  in  which  naphtha  and  water  collect,  and  are  easily  separated.  In  some 
parts  of  this  district  so  much  combustible  gas  or  vapour  rises  from  the 
ground,  that  when  set  on  fire,  it  continues  burning,  and  even  affords  heat  for 
economical  purposes.  A  large  quantity  of  an  impure  variety  of  petroleum 
comes  from  the  Birman  territory  in  the  East  Indies:  the  country  consists  of 
sandy  clay,  resting  on  a  series  of  alternate  strata  of  sandstone  and  shale. 
Beneath  these  occurs  a  bed  of  pale  blue  shale  loaded  with  petroleum,  which 
lies  immediately  on  coal.  A  petroleum-spring  exists  at  Colebrook  Dale,  in 
Shropshire.  The  sea  near  the  Cape  de  Vei'de  Islands  has  been  seen  covered 
with  a  film  of  rock-oil.  The  finest  specimens  of  naphtha  are  furnished  by 
Italy,  where  it  occurs  in  several  places. 

In  proof  of  the  origin  attributed  to  these  substances,  an  experiment  of 
Dr.  Reichenbach  may  be  cited,  who,  by  distilling  with  water  about  100  lb.  of 
pit-coal,  obtained  nearly  2  ounces  of  an  oily  liquid  exactly  resembling  the 
natural  naphtha  of  Amiano,  in  the  Duchy  of  Parma. 

The  variations  of  colour  and  consistence  in  different  specimens  of  these 
bodies  certainly  depends  in  great  measure  upon  the  presence  of  pitchy  and 


532  PETROLEUM,     NAPHTHA,     ETC. 

fatty  substances  dissolved  in  the  more  fluid  oil.  Dr.  Gregory  found  paraffin 
in  petroleum  from  Rangoon. 

The  boiling-point  of  rock-oil  varies  from  about  180°  to  near  600°  (82° -2 
to  315° -50) ;  a  thermometer  inserted  into  a  retort  in  which  the  oil  is  under- 
going distillation,  never  shows  for  any  length  of  time  a  constant  tempera- 
ture. Hence  it  is  inferred  to  be  a  mixture  of  several  different  substances. 
Neither  do  the  different  varieties  of  naphtha  give  similar  results  on  analysis ; 
they  are  all,  however,  carbides  of  hydrogen.  The  use  of  these  substances 
in  the  places  where  they  abound  is  tolerably  extensive  ;  they  often  serve  the 
inhabitants  for  fuel,  light,  &c.  To  the  chemist  pure  naphtha  is  valuable,  as 
offering  facilities  for  the  preservation  of  the  more  oxidable  metals,  as  potas- 
sium and  sodium. 

The  following  are  of  rarer  occurrence  : — 

Reiiniie,  or  Retinasphalt,  is  a  kind  of  fossil  resin  met  with  in  brown  coal ; 
it  has  a  yellow  or  reddish  colour,  is  fusible  and  inflammable,  and  readily 
dissolved  in  great  part  by  alcohol.  The  soluble  portion  has  been  called 
retime  acid  by  Prof  Johnston.  Hatchetin  is  a  somewhat  similar  substance 
met  with  in  mineral  coal  at  Merthyr-Tydvil,  and  also  near  Loch  Fyne,  in 
Scotland.  Idrialin  is  found  associated  with  native  cinnabar,  and  is  extracted 
from  the  ore  by  oil  of  turpentin,  in  which  it  dissolves.  It  is  a  white,  crys- 
talline substance,  scarcely  volatile  without  decomposition,  but  slightly  soluble 
in  alcohol  and  ether,  and  composed  of  04911,40  ;  it  is  generally  associated 
with  a  hydrocarbon  idryl,  which  contains  C42H14. 

Ozokerite,  or  fossil  wax,  is  found  in  Moldavia,  in  a  layer  of  bituminous 
shale ;  it  is  brownish  and  has  a  somewhat  pearly  appearance ;  it  is  fusible 
below  212°  (100°C),  and  soluble  with  difficulty  in  alcohol  and  ether,  but 
easily  in  oil  of  turpentin.  It  appears  to  contain  more  than  one  definite 
principle. 


APPENDIX. 


i5« 


(688) 


534 


APPENDIX. 


HYDROMETER    TABLES 


OOHPARIBON    OF   THE    DEGEEES    OF   BAUME's   HTDEOMETEE   WITH   THE   EEAl 
SPECIFIC    GRAVITIES. 


1.  For  liquids  heavier  than  water. 


Degrees. 

Specific 
Gravity. 

Degrees. 

Specific 
Gravity. 

Degrees. 

Specific 
Gravity. 

0 

1000 

26 

1-206 

52 

1-520 

1 

1-007 

27 

1-216 

53 

1-535 

2 

1013 

28 

1-225 

54 

1-551       • 

3 

1-020 

29 

1-235 

55 

1-567 

4 

1-027 

30 

1-245 

56 

1-583 

5 

1-034 

31 

1-256 

57 
58 

1-600 

6 

1041 

32 

]'24T 

1-617 

7 

1048 

83 

l-27f 

59 

1-634 

8 

1056 

34 

1-288 

60 

1-652 

9 

1063 

35 

1-299 

61 

1-670 

10 

1070 

36 

1-310 

62 

1-689 

11 

1-078 

37 

1-321 

63 

1-708 

12 

1085 

38 

1-333 

64 

1-727 

13 

1-094 

39 

1-345 

65 

1-747 

14 

1-101 

40 

1-357 

66 

1-767 

16 

1-109 

41 

1  369 

67 

1-788 

16 

1-118 

42 

1-381 

68 

1-809 

17 

M26 

43 

]  -395 

69 

1-831 

18 

1-134 

44 

1  -407 

70 

1-854 

19 

1143 

45 

1  420 

71 

1-877 

20 

M52 

46 

1-434 

72 

1-900 

21 

1-160 

47 

1-448 

73 

1-924 

22 

1-169 

48 

1-462 

74 

1-949 

23 

1-178 

49 

1-476 

75 

1-974 

24 

M88 

50 

1-490 

76 

2-000 

25 

1-197 

51 

1-495 

APPENDIX. 


58^ 


2.  Baume's  Hydrometer  for  liquids  lighter  than  water. 


Degrees. 

Specific 
Gravity. 

Degrees. 

Specific 
Gravity. 

Degrees. 

Specific 
Gravity. 

10 

1000 

27 

0-896 

44 

0-811 

11 

0-993 

28 

0-890 

45 

0-807 

12 

0-986 

29 

0-885 

46 

0-802 

13 

0-980 

30 

0-880 

47 

0-798 

14 

0-973 

31 

0-874 

•    48 

0-794 

15 

0-967 

32 

0-869 

49 

0-789 

16 

0-960 

33 

0-864 

50 

0-785 

17 

0-954 

34 

0-859 

51 

0-781 

18 

0-948 

35 

0-854 

52 

0-777 

19 

0-942 

36 

0-849 

53 

0-773 

20 

0-936 

37 

0-844 

54 

0-768 

21 

0-930 

38 

0-839 

55 

0-764 

22 

0-924 

39 

0-834 

56 

0-760 

23 

0-918 

40 

0-830 

57 

0-757 

24 

0-913 

41 

0-825 

58 

0-753 

25 

0-907 

42 

0-820 

59 

0-749 

26 

0-901 

43 

0-816 

60 

0-745 

These  two  tables  are  on  the  authority  of  M.  Francoeur ;  they  are  taken 
from  the  Handworlerbuch  der  Chemie  of  Liebig  and  Poggendorff.  Baum^'a 
hydrometer  is  very  commonly  used  on  the  Continent,  especially  for  liqtiidg 
heavier  than  water.  For  lighter  liquids,  the  hydrometer  of  Cartier  is  often 
employed  in  France,  Cartier's  degrees  differ  but  little  from  those  of 
Baum6. 

In  the  United  Kingdom,  Twaddell's  hydrometer  is  a  good  deal  used  for 
dense  liquids.  This  instrument  is  so  graduated  that  the  real  sp.  gr.  can  be 
deduced  by  an  extremely  simple  method  from  the  degree  of  the  hydrometer, 
namely,  by  multiplying  the  latter  by  5,  and  adding  1000 ;  the  sum  is  the 
sp.  gr.,  water  being  1000.  Thus  10°  Twaddell  indicates  a  sp.  gr.  of  1050, 
or  1-05;  90°  Twaddell,  1450,  or  1-45. 

In  the  Customs  and  Excise,  Sike's  hydrometer  is  used. 


536 


APPENDIX. 


ABSTRACT 

OF   DE.    DALTON's    TABLE    OP   THE    ELASTIC    FORCE   OF   VAPOUR   OF   WATER   AT 
DIFFERENT   TEMPERATURES,    EXPRESSED    IN   INCHES    OF   MERCURY. 


Temperature. 

Temperature. 

Temperature. 

Force. 

Force. 

Force. 

Fah. 

Cent. 

Fah. 

Cent 

Fah. 

Cent. 

32° 

Oo-O 

0-200 

57° 

13°-88 

0-474 

90° 

32° -2 

1-36 

33 

0°-55 

0-207 

58- 

140.4 

0-490 

95 

35° 

1-58 

34 

1°-1 

0-214 

59 

15° 

0-507 

100 

870.77 

1-86 

35 

l°-66 

0-221 

60 

15°-5 

0-524 

105 

40° -5 

2-18 

36 

2° -2 

0-229 

61 

16°-1 

0-542 

110 

43°-3 

2-53 

37 

2°-77 

0-237 

62 

j6°-66 

0-560 

115 

46°-l 

2-92 

38 

3°-3 

0-245 

63 

17°-2 

0-578 

120 

48° -88 

3-33 

39 

3°-88 

0-254 

64 

170.77 

0-597 

125 

51°-66 

3-75 

40 

40.4 

0-263 

65 

]8°-3 

0-616 

130 

54° -4 

4-34 

41 

5° 

0-273 

66 

18°-88 

0-635 

135 

57°-2 

5-00 

42 

5°-55 

0-283 

67 

19°-4 

0-665 

140 

60° 

5-74 

43 

6°-l 

0-294 

68 

20° 

0-676 

145 

62°-77 

6-53 

44 

6°-66 

0-305 

69 

20° -55 

0-698 

150 

65°-5 

7-42 

45 

7°-2 

0-316 

70 

21°-1 

0-721 

160 

71°-1 

9-46 

1  46 

70.77 

0-328 

71 

21°-66 

0-745 

170 

76°-66 

12-13 

47 

8°-3 

0-339 

72 

22°-2 

0-770 

180 

82°-2 

15-15 

48 

8°-88 

0-351 

73 

22°-77 

0-796 

190 

87°-77 

1900 

49 

90.4 

0-363 

74 

23°-3 

0-823 

200 

93°-3 

23-64 

50 

10° 

0-375 

75 

23°-88 

0-851 

210 

98° -88 

28-84 

51 

10°-55 

0-388 

76 

24°-4 

0-880 

212 

100° 

3000 

52 

11°-1 

0-401 

77 

25° 

0-910 

220 

104°-4 

34-99 

53 

110-66 

0-415 

78 

25°-5 

0-940 

230 

110° 

41-75 

54 

12°-2 

0-429 

79 

26°-l 

0-971 

240 

115°-5 

49-67 

55 

12°-77 

0-443 

80 

26°-66 

1-000 

250 

121°-1 

58-21 

56 

13°-3 

0-458 

85 

29° -44 

1-170 

300 

148°-88 

111-81 

APPENDIX. 


537 


TABLE 

OP  THE  PBOPOETION  BY  WEIGHT  OF  ABSOLUTE  OR  REAL  ALCOHOL  IN  100  PABT8 
OF    SPIRITS    OP   DIFFERENT    SPECIFIC   GRAVITIES.       (FOWNES.) 


Sp.Gr.  at60° 
(150-5C). 

Per  cent, 
of  real 
Alcohol. 

Sp.  Gr.  at  60° 
(150-60.) 

Per  cent, 
of  real 
Alcohol. 

Sp.  Gr.  at  60° 
(150-5C). 

Per  cent, 
of  real 
Alcohol. 

0-9991 

0-5 

0-9511 

34 

0-8769 

68 

0-9981 

1 

0-9490 

35 

0-8745 

69 

0-9965 

2 

0-9470 

36 

0-8721 

70 

0-9947 

3 

0-9452 

37 

0-8696 

71 

0-9930 

4 

0-9434 

38 

0-8672 

-   72 

0-9914 

5 

0-9416 

39 

0-8649 

73 

0-9898 

6 

0-9396 

40 

0-8625 

74 

0-9884 

7 

0-9376 

41 

0-8603 

75 

0-9869 

8 

0-9356 

42 

0-8581 

76 

0-9855 

9 

0-9335 

43 

0-8557 

77 

0-9841 

10 

0-9314 

44 

0-8533 

78 

0-9828 

11 

0-9292 

45 

0-8508 

79 

0-9815 

12 

0-9270 

46 

0-8483 

80 

0-9802 

13 

0-9249 

47 

0-8459 

81 

0-9789 

14 

0-9228 

48 

0-8434 

82 

0-9778 

15 

0-9206 

49 

0-8408 

83 

0-9766. 

16 

0-9184 

50 

0-8382 

84 

0-9753 

17 

0-9160 

51 

0-8357 

85 

0-9741 

18 

0-9135 

52 

0-8331 

86 

0-9728 

19 

0-9113 

53 

0-8305 

87 

0-9716 

20 

0-9090 

54 

0-8279 

88 

0-9704 

21 

0-9069 

55 

0-8254 

89 

0-9691 

22 

0-9047 

56 

0-8228 

90 

0-9678 

23 

0-9025 

67 

0-8199 

91 

0-9665 

24 

0-9001 

58 

0-8172 

92 

0-9652 

25 

0-8979 

69 

0-8145 

93 

0-9638 

26 

0-8956 

60 

0-8118 

94 

0-9623 

27 

0-8932 

61 

0-8089 

95 

0-9609 

28 

0-8908 

62 

0-8061 

96 

0-9593 

29 

0-8886 

63 

0-8031 

97 

0-9578 

30 

0-8863 

64 

0-8001 

98 

0-9560 

31 

0-8840 

65 

0-7969 

99 

0-9544 

32 

0-8816 

66    . 

0-7938 

100 

0-9528 

33 

0-8793 

67 

i 

538 


APPENDIX. 


DR.    SCHWEITZER'S 

OF   THE    PKINCIPAL    MINERAL   WATERS    OF   GERMANS 


Grains  of  Anhydrous 

Ingredients  in 

One  Pound  Troy. 

Carlsbad. 

Ems. 

Schlesischer. 
Obersalz- 
Brunnen. 

Carbonate  of  Soda 

7-2712 
0-0150 

0*0655 
1-7775 
1-0275 
0-0048 
00208 
0-0012 
00019 

14-9019 

6-9820 

0-oi84 
0-4329 

8-0625 
0-0405 
0-0022 
00080 
0-8555 
0-5915 
0-0028 
0-0120 

0-*66l4 
0-4050 

0-0338 
6-7255 

0-'6bl4 
0-3 104 

7-6211 

0-0170 
1-5464 
1-5496 
0-0026 
0-0356 

0-3160 
2-5106 

0-01*64 

0-'8682 

0-"6051 
0-'2423 

Ditto  of  Lithia 

Ditto  of  Baryta 

Ditto  of  Strontia 

Ditto  of  Lime 

Ditto  of  Magnesia 

Ditto  (proto)  of  Manganese 
Ditto  (proto)  of  Iron....... 

Sub-Phos.  of  Lime .- 

Ditto  of  Alumina 

./ 

Sulphate  of  Potassa 

Ditto  of  Soda 

Ditto  of  Lithia 

Ditto  of  Lime 

Ditto  of  Strontia 

Ditto  of  Magnesia 

Nitr.  of  Magnesia 

Chlor.  of  Ammonium 

Ditto  of  Potassium 

Ditto  of  Sodium 

Ditto  of  Lithium 

Ditto  of  Calcium 

Ditto  of  Magnesium 

Ditto  of  Strontium 

Bromide  of  Sodium 

Iodide  of  Sodium 

Fluoride  of  Calcium 

Alumina 

Silica 

Total 

Carbonic  Acid  Gas  in  100 
cubic  inches 

Temperature - 

} 

31-4606 
68 

Sprud.  165° 
(73°-8C) 

Neub.    138° 
(58° -8C) 

Muhl.    128° 
(53°-3C) 

Ther.     122° 
(50°C) 

Berzelius. 

160525 
61 

Kess.  117° 

(47° -2C) 

Kran.    84° 

(28° -8C) 

Struve. 

14-7809 
98 

58°  (14°  5C) 
Struve.     • 

Analyzed  by 

APPENDIX, 


539 


TABLE   OF  ANALYSES 

AND   OF   THE    SABATOQA   CONGRESS    SPRINO   OF    AMERICA. 


Saratoga 
Congress 
Spring. 

Kissengen. 
Ragozi. 

Marienbad. 
Kreutbr. 

Auschowitz. 

Ferdinands- 

Brunnen. 

Eger. 
Franzens- 
Brunnen- 

0-8261 

0-0672 
5-8531 
4-1155 
00202 
0-0173 

0-1379 

0-1004 

00326 

1-6256 

19-6653 

0-1613 
0-0046 

0-0069 
0-1112 

0-*6592 
4-8180 
1-3185 
00121 
0-1397 

1-2540 

5-5485 

0-0364 
39-3733 

3-6599 

0-'3331 

0-1609 

5-3499 
00858 

0-*6028 
2-9509 
2-0390 
20288 
0-1319 

28-5868 

;;;;;; 

10-1727 


0-6623 
0-2908 

4-5976 
0  0507 

0-6640 
3-0085 
2-2867 
00692 
0-2995 

0-6640 

16-9022 

6-7472 



0-5023 

3-8914 
0-0282 

0-6623 
1-3501 
0-5040 
00322 
01762 
0-0172 
0-0092 

18-3786 
6-9229 

0-3548 

32-7452 
114 

50°  (10°C) 
Schweitzer. 

56-7136 
96 

53°  (11°-6C) 
Struve. 

51-6417 
105 

53°(11°-6C) 
Berzelius. 

34-4719 
146 

49°  (9°-5C) 
Steinman. 

31-6670 
154 

54°  (12°-2C) 
Berzelius. 

540 


APPENDIX. 


DR.    SCHWEITZER'S 

OF   THE    PRINCIPAL    MINERAL   WATERS    OF   GERMANY 


Grains  of  Anhydrous 

Ingredients  in 

One  Pound  Troy. 

Pyrmont. 

Spa  Pouhon. 

Fachingen. 

Carbonate  of  Soda 

4*7781 

0-0364 
0-3213 

o'-ono 

0-0314 
1-6092 
0-0067 
5-0265 
0-0154 
2-3684 

0-8450 

0-*37'27 

0-5531 

0-7387 
0-8421 
00389 
0-2813 
00102 
00064 
0-0593 
0  0281 

0-3371 
0-'3739 

12-3328 

1-8667 
1-2983 

0-0061 

0-1267 

3-2337 
0-0657 

Ditto  of  Lithia 

Ditto  of  Baryta 

Ditto  of  Strontia 

Ditto  of  Lime 

Ditto  of  Magnesia 

Ditto  (proto)  of  Manganese 

Ditto  (proto)  of  Iron 

Sub-Phos.  of  Lime 

Ditto  of  Alumina 

Sulphate  of  Potassa 

Ditto  of  Soda 

Ditto  of  Lithia 

Ditto  of  Lime 

Ditto  of  Strontia 

Ditto  of  Magnesia 

Nitr.  of  Magnesia 

Chlor.  of  Ammonium 

Ditto  of  Potassium ,. 

Ditto  of  Sodium 

Ditto  of  Lithium 

Ditto  of  Calcium 

Ditto  of  Magnesium 

Ditto  of  Barium 

Ditto  of  Strontium 

Bromide  of  Sodium 

Iodide  of  Sodium 

Fluoride  of  Calcium 

Alumina 

Silica 

Total 

15-4221 
160 

56°  (13°-3C) 
Struve. 

3-2691 

136 

50°  (10°C) 
Struve. 

18-9300 
135 

50°  (10°C) 
Bischoff. 

Carbonic  Acid  Gas  in  100  \ 
cubic  inches j 

Temperature  (F.) 

Analyzed  bv 

APPENDIX, 


541 


TABLE   OF   ANALYSES 

AND    OF   THE    SARATOGA   CONGRESa    SPRING   OF   AMERICA,  Continued. 


Selters. 

Sfndschiitz. 

Pailna. 

Kreuznacb. 

Elisen- 

Brunneu. 

Adelheids- 
Quelle. 

4-6162 

5-2443 
0-0902 

00014 

0-0024 

0-0144 

0-0387 

1-4004 

5- 1045 

0-5775 

0-2058 

0-4703 

1-5000 

0-8235 

4-8045 

1-1812 

0-2980 

00032 

0-0072 

0-OOli 

0-0095 

0-1495 

0-0121 

0-0007 

00117 

0-0026 

0-0020 

0-0088 

0-2978 
•••••• 

3-6705 
17-6220 

l'-1287 

00347 

62-3535 

5-9802 

3-6000 
92-8500 

l*-956o 

69-8145 



0-0066 

0-*2685 

•••••. 

0-7287 

0-1845 

12-9690 

l-'2225 

14-7495 

54-6917 
0  0562 
9-7358 

0-2366 

28-4608 

.  .... 





0-5494 
0-2304 
00024 

0-3060 
0-1500 

0-()6i3 



0'0086 

0-0166 

0-2265 

0-0900 

0-1320 

0-2355 

0-1922 

21-2982 

98-0133 

188-4806 

68-0190 

35-4739 

126 

20 

7 

12 

10 

58°  (14°-5C) 

58°  (14°-5C) 

58°  (14°-5C) 

47°  (8°-3C) 

58°  (14°-5C) 

Struve. 

Struve. 

Struve. 

Struve. 

Struve. 

46 

M2  APPENDIX. 


WEIGHTS   AND    MEASURES 


480-0  grains  Troy  =  1  oz.  Troy. 

437*6  **  =1  oz.  Avoirdupoida. 

7000-0  "  =  1  lb.  Avoirdupoida. 

6760-0  "  =1  lb.  Troy. 


The  imperial  gallon  contains  of  water  at  60°  (15° -50)  70,000-    grains 

The  pint  (^  of  gallon) 8,750-         *' 

The  fluid-ounce  (^\  of  pint) 437-6       " 

The  pint  equals  34-66  cubic  inches. 


The  French  kilogramme  =  16,433-6  grains,  or  2-679  lb.  Troy,  or 

2-205  lb.  avoirdupoida. 

The  grammme       =  15-4836  grains. 

**    decigramme    =    1-5434       " 

"    centigramme  =    0-1543       " 

"    milligramme  =    0-0154       ** 


The  mitre  of  France  =  39-37      inchei. 
«'    decimltre  =    3-937         " 

"    centimltre  =    0-394         *« 

"    millimUre  =    0  0394       *• 


INDEX, 


Page 

A  BSORPTiox  of  heat 80 

Acer  saccharinum 334 

Acetal 371 

Acftarakle 356 

Acetate  of  acetetyl 215 

Acetate  of  oxide  of  amyl...  389 

Acetates 373 

A.etetyl 215 

Acetic  acid ~ 371,  395 

anhydrous 214,215 

ether 356 

Acetine 483 

Acetone 376 

Acotonitrile 373 

Acetyl 369 

Acid,  acetic 371,  395 

anhydrous 214,  215 

aconitic 414 

acrylic 487 

aldehydic 370 

alloxanic 440 

alphaorsellic 475 

althionic 366 

amalic 460 

amvgdalic 423 

aniiic 406,473 

anilotic 406 

anisic 490 

anthranilic 459,  474 

antimonic 288 

arsenic 292 

arsenious 291 

aspartic 416,452 

auric 300 

azoUc 123 

balenic. 395 

henzilic 401 

benzoic 396 

anhydrous 215 

betaorsellic 475 

biamuthic 275 

boracic 151 

bromic 148 

bromo-hydrosalicylic...  405 

bromo-phenisic 528 

butyric 393,  485 

cainpholic , 492 

camphoric 492 

capric 394.  485 

caproic 394,  4''5 

caprylic 394,485 

carbazotic 473 

carbolic 526 

carbonic 129 

liquefaction  of. 63 

carminic 477 

cerebric 517 

cerc'tic 4&6 


Acids  —  contimied.  Page 

cerotylic 394 

cetylic 394,  486 

chelidonic 447 

chloracetic 318,  375 

chlorhydric 141 

chloric 145 

chlorocarbonic 131 

chlorochromic 269 

chlorohydrosalicylic 405 

chlorohyponitric 143 

chloronaphthalic 530 

chloroni<*ic 463 

chloronitrous 143 

chlorophenisic 528 

chlorosulphuric...  136,  364 

chlorous 144 

chlorovalerisic 393 

chlorovalerosic 393 

cholalic 510 

choleic 510 

choloidinic 511 

chrysammic 479 

chrysanilic 459,  473 

chrysolepic 479 

chrysophanic 477 

chromic 268 

cinnamic 407 

citraconic 414 

citric 413 

cocinic 484 

comenic 447 

croconic 345 

cumaric 407 

cumio 403,491 

cyanic 426 

cyanuric 426,  427 

delphinic 485 

dextro-racemic 413 

dialuric 442 

dithionic 135 

draconic 491 

elaidic 484 

ellagic 418 

equisetic 414 

erythric 474 

ethalic 486 

ethionic 366 

euchronic 345 

euxanthic 479 

evernic 475 

eTerninic 476 

ferric 261 

formic 385,394 

formobenzoic 400 

fulminic 428 

fumaric 416 

{THllic 416,418 

glyco-benzoic 402 


Acids  —  cont.  Paob 

glyco-cholalic 510 

glyco-hyo-cholalic 512 

glycolic 402,501 

glucic .339 

hemipinic 4^ 

hippuric 4(W' 

huraic 336 

hydriodic 147 

hydrobromic 148 

hydrochloric 141 

hydrocyanic 420 

hydroferricyanic 433 

hydroferrocyanic 430 

hydrofluoric 149 

hydrofluosilicic 149 

hydroleic 487 

hydromargaric 487 

hydromargaritic 487 

hydrosalicylic 404 

hydrosulphocyanic 435 

hydrosulphuric 103 

hyocholalic 512 

hyocholic 511 

hypochloric 144 

hypochlorous 144 

hyponitric 126 

hypophosphorous 138 

hyposulphobenzic 398 

hyposulphuric,  sulphu- 
retted   135 

hyposulphurous 135 

igasuric 449 

indinic 472 

inosinic 503 

itaconic 414 

iodic 147 

iodo-sulphuric 136 

isatinic 472 

isethionic 345 

japonic 418 

kakodyJic 379 

kalisaccharic 336 

kinie 447,448 

lactic 349 

lecanoric 475,  476 

levo-racemic 413 

lithic 433 

lithofellinic 512 

malamic 415 

maleic 416 

malic 414 

manganic 259 

margaric 481 

meconic 446 

melanic 404 

melasiuic. ...  336 

raclissic 39* 

mellitic 3U 


544 


INDEX. 


Kcws  —  cont  Page 

mesoxalic 440 

mctacetonic 376 

metagallic 419 

metamargaric 488 

metapectic 340 

inetaphoRphoric. 213 

methionic 306 

metoleic 4R7 

mucic 344 

muriatic 141 

mykomelinic 440 

myristic 484 

myronic 493 

nitric 123 

nitrasinic 490 

•nitrobenzoic 397 

nitrococcusic 477 

nitrocumio 403 

nitrophenasic 528 

nitrophenesic 528 

^.+      nitrophenisic 528 

nitrosalicylic 406,4"^' 

nitrotoluylic 4 

nitrous 126 

renanthic 257 

oenanthylic 395,488 

oleic 482 

oleophosphoric 517 

opianic 445 

orsellinic 474,475 

oxalic 341 

oxalovinic 359 

oxaluric 440 

oxamic 343 

oxalinic 461 

palmitic 484 

parabanic 440 

paratartaric 413 

purellic 476 

poetic 341 

polargonic 357,  395 

pnntathionic 136 

perchloric 145 

perchromic 269 

periodic 148 

permanganic 259 

phoceni-   485 

jvhosphethylic: 359 

phosphohiethylik. 359 

phosphoric 138 

anhydrous 213 

bibasic 213 

glacial 213 

monobasic 213 

tribasic 212 

phosphorous 138 

phosphovinic 358 

phthalic... 529 

picric 473 

pimaric 494 

pinic 493 

propionic , 376,395 

prussic 420 

Durpuric 443 

purreic 479 

pyrogallic 419 

pyromeconic 447 

pyromucic 345 

pyrophosphoric 213 

pyrotartaric •...  412 

racemic 413 

retinic 5:>'2 

rhodizonir 345 


Acins  —  cont.  Page 

ricinoleic 488 

rubiacic 478 

ruble 418 

saccharic 343 

sncchulmic 336 

salicylic 406 

salicylous 404 

sebacic 484 

selenic 136 

selenious.. 136 

stearic 481 

styphnic 479 

suberic 345,484 

succinic 484 

sulphamylic 390 

sulphindigotic 471 

pulphindylic 471 

sulphobenzoic 398 

Bulphoglyceric 4R3 

sulpholeic 487 

sulphomargaric 487 

sulphomethylic 383,  384 

Bulphonaphthalic 529 

sulphophenic 526 

sulphosaccharic 335 

sulphotoluolic 495 

eulphovinic 358 

sulphuric 133 

sulphuric,  anhydrous...  135 

sulphurous 132 

eylvic 493 

tannic 416 

tartaric 410 

tartaric,  anhydrous 412 

tartralic 412 

tartrelic 412 

lartrovinic 359 

tauro-cholalic 511 

tauro-hyo-cholalic 512 

telluric 290 

tellurous 290 

tetrathionic 135 

thionuric 441 

tnluylic .....' 403 

trithionic 135 

ulmic 336 

uramilic 441 

uric 436,  438 

usnic 476 

valerianic 390,  395 

valeric 390,  395,  492 

xanthic 368 

salts 202 

anhydrous 214 

bibasic 212 

fatty 345 

hydrogen- theory  of. 214 

monobasic 212 

notation  of. 213 

oxygen- theory  of 214 

polybasic 212 

terminology  of 132 

tribasic 212 

vegetable 410 

Aconitates 414 

Aconitic  acid 414 

Acouitine 451 

Aconituirt,  acid  of 414 

Aconitiim  napellus 451 

Acrolein 482,487 

Acrylic  acid 487 

Affinity,  chemical 183 

Aftpr-damp  of  coal-miner.  12P 


i'AOI 

Air-pum;  34,  36 

Air,  atmospheric 120 

Alanine 350,  370,  467 

Albite 250 

Albumin 495 

Albuminous  principles....  496 

Alcohol 346 

absolute 34(5 

butyl- 392,  395 

capryl- 395,  488 

cerotyl- 395,  486 

cetyl- 395,  48(5 

ethal- 486 

Alcohols,  generally 393 

Alcohol,  melissic 394,  486 

table  of,  in  aqueous  mix- 
tures   537 

Aldehyde 851,  379 

ba.ses  from 467 

resin" 370 

Aldehydic  acid 370 

Alembruth,  sal 305 

Algaroth,  powder  of. 289 

Alizarin 477 

Alkalimeter 227 

Alkalimetry 226 

Alkaloids 444 

artificial 463 

Alkargen 379 

Alkarsin 377 

Allantoin 438 

AUiaria  officinalis,  oil  of..  493 

Alloxan 439 

AUoxanin  acid 440 

Alloxantin 441,451 

Alloys 199 

of  copper 278 

Allyl 493 

oxide  of. 493 

sulphide  of 493 

sulphocyanide  of. 493 

Almonds,  oil  of  bitter 39P 

Aloes 479 

Alphaorsellic  acid 475 

Althionic  acid 366 

Alums  249 

Alum,  common 249 

Roman 249 

Alumina 248 

.acetate  of 373 

analytical  remarks  on..  25C 

silicates  of 249 

sulphate  of 249 

Aluminium 248 

chloride  of 248 

Alum  stone 249 

Amalgam,  ammoniacal...  2"!2 

Amalgam 199,  306 

Amalic  acid 450 

Amarine 401,  466 

Amber 484,  494 

Amidin ,"^38 

Amidogen 235 

Amidogen-bases 454 

Ammeiide 436 

Ammeline 436 

Ammonia 162 

acetate  of. 373 

alum 249 

analytical  remarks  on..  235 

benzoate  of 397 

cyanate  of 427 

rnalate  rf  .415 


INDEX. 


545 


Ammoxia  —  roni.  Pagb 

oxalate  of 343 

purpurate  of 442 

tartrate  of 411 

urate  of 438 

Ammonium 201,2.32 

cyanide  of. 425 

ferrocyanide  of. 433 

palicylide  of 404 

Amnii  liquor 508 

Amorphous  quinine 448 

Amy^'dalic  acid 423 

Amygdalin  396,  423 

Amyiaceou.s  group 333 

Amyl  and  its  compounds  3S8 

series,  bases  of  the 458 

Amylamine 458 

-urea 458 

Amvl-ammonia 458 

Amylene 390 

Amylic  ether 389 

mercaptan 390 

Amylotriethyl  -  ammo- 
nium, oxide  of 464 

Analcime 250 

Analy.sis,  ultimate,  of  or- 
ganic bodies 320 

Analysis  of  carbonates....  228 
Analytical  method  of  che- 
mical research 115 

Anhydrous  acids 214 

Anil'ic  acid 406,  473 

Aniline 399,459,463 

homologues  of 462 

-urea ^2 

Anilotic  acid 406 

Animal  heat 507 

body,  components  of....  496 

Aniseed,  oil  of. 490 

Anisic  acid  490 

Anisoin 490 

Anisol 491 

Auisyl,  hydride  of. 490 

Anthranilic  acid 459,  474 

Antiarin  452 

Antimonic  acid 288 

Antimony 287 

bases 469 

crude  289 

potassa,  tartrate  of. 411 

Aqua  regia 143 

Arabin 340 

Archil 474 

Argand  lamp 169 

Argol..- 347,  410 

Aricine 448 

Aridium 266 

Arragonite 242 

Arrow  poison  of  central 

America 451 

Arrowroot 339 

Arsenic  acid 292 

Arsenic    and    its    com- 
pounds   291 

analytical  details 293 

detection     in    organic 

mixtures 293 

Arsenious  acid 291 

Artemisia 4.52 

Arterial  blood 503 

Assafoetida 479 

oil  of 493 

Asparagin 415,  452 

Af^fMAjrus 452 

4<j* 


Page 

Aspartic  acid 415,  452 

Aspen .-...  452 

Asphaltene 531 

Aspbaltum 531 

Astatic  needle 101 

Atmosphere,  chemical  re- 
lations of 120 

composition   and    anar 

lysis  of. 121 

physical  constitution  of    34 

purifying 244 

Tapour  of  water  in 61 

Atmospheric  electricity...    97 

Atomic  theory 182 

Atomic  weight 183 

Atoms 182 

Atropa  belladonna 451 

Atropine 451 

Attenuation  of  wort 348 

Attraction 183 

Augite 247 

Auric  acid 300 

Auschowitz,  water  of. 539 

Axes  of  crystals 206 

Axiuite 250 

Azobenzol 399 

Azotic  acid 123 

B. 

Badian-oil 491 

Balenicacid 395 

Balsams 493 

Balsam,  Canada 494 

copaiba 494 

Peru  408,  495 

Tolu 403,408,495 

Barilla 225 

Barium  237 

ferrocyanide  of. 432 

salicylide  of 404 

Barley  STigar 334 

Barometer 38 

Baryta  and    its   hydrate 

237,  2.38 

acetate  of. 373 

analytical  remarks  on..  238 

aconitate  of. 414 

fulminate  of 429 

tartrate  of. 411 

Bases 109 

from  aldehyde 467 

amidogen- 454 

from  animal  oil 4<i5 

antimony- 469 

organic,   containing 

chlorine 460 

from  coal-tar-oil 465 

of  the  ethyl-series 455 

imidogen- 454 

artificial,  containing 

mercury , 306 

mixed  artificial 463 

nitrile- 454 

from  Tolatile  oils  by 

ammonia 465 

organic 444 

organic,  artificial 453 

phosphorus- 468 

containing  platinum....  309 

Bassorin 340 

Battery,  constant 193 

Baume's  hydrometer 535 

Bay  Bait  ......  232 


Paqs 

Beeberine 451 

Beer 347 

Beetroot,  sugar  from 334 

Bell  metal 279 

Bengal  light 290 

Benzamide 40O 

Benzile 401 

Benzilic  acid 401 

Benzimide 401 

Benzine 398 

Beuzoates 397 

Benzoate  of  benzoyl 215 

of  phenyl 527 

Benzoic  acid 396,  452 

anhydrous 215 

Benzoicine 483 

Benzoin 480 

Benzol 398 

Benzol,  homologues  of....  402 

Benzoline  46Q 

Benzone 398 

Benzonitrile 401 

Benzophenone 398 

Benzoyl 401 

and  its  compounds 390 

benzoate  of 218 

Berberine 451 

Berberis  vulgaris 451 

Bergamot,  oil  of. 490 

Berthollet's    fulminating 

silver 299 

Beryl 251 

Berylla 251 

Beryllium 250 

Betaorcin 476 

Betaorsellic  acid 475 

Bezoar  stones 512 

Biamylamine 468 

Biamvl-ammonia 458 

Bibaslc  acids 212 

Biborate  of  soda 231 

Bicarbonate  of  potassa....  221 

Bicarbonate  of  soda 226 

Bichloraniline 460 

Bichlorethyl  amine 455 

Bichloride  of  tin 283 

Bichlorisatin 473 

Bichlorokinone 449 

Bichlorosaligenin 406 

Bichromate  of  potassa 269 

Biethylamine 456 

-urea 458 

Biethyl-ammonia 456 

Biethyl-amylamine 464 

Biethylaniline 463 

Biethyl-phenylaiftine 463 

Biethyl-phenyl-ammo- 

nium,  oxide  of 463 

Biethylo-toluldine 463 

Biliary  calculi 487 

Bile 509 

test  of  Pettenkofer 511 

Bilin 511 

Bimethylamine 458 

Binai-y  theory  of  salts 213 

Binitrobenzol 399,  460 

Binitrotoluol 495 

Binoxide  of  barium 237 

of  protein 500 

of  tin 282 

Biscuit 264 

Bismuth 274 

Analytical  remarks 274 


516 


INDEX 


Pace 

Bismutbic  acid '21b 

Bisulphate  of  potassa 221 

of  soda 229 

Bisulphide  of  carbon 169 

Bitter  almonds,  oil  of 396 

Bitumen 530 

compact 531 

elastic 531 

Black  flux 294 

Bleaching 244 

Bleaching  powder 243 

testing  its  value 244 

salts 144 

Blende 273 

Blood 503 

arterial 503 

circulation  of  the 503 

corpuscles 504 

discs 504 

globules 504 

^  serum  of. 504 

■    venous 503 

Blowpipe 168 

Blue  ink 432 

light 290 

Prussian 432 

Turnbull's 433 

Boilers,  deposits  in 242 

Boiling  point 54 

Bones 518 

Boracic  acid 151 

ether 355 

Borax 231 

Borneene 492 

Borneol 492 

Boron 151 

chloride  of. 169 

fluoride  of 161 

Brass 278 

Brazilwood 478 

Bread 349 

Brewing 348 

British  gum SIW 

Bromal 367 

Bromanlline 400 

Bromanisal 491 

Bromic  acid 148 

Bromide  of  amyl 689 

of  arsenic Zi2 

of  benzoyl 400 

of  cyanogen 430 

of  ethyl 353 

of  potassium 224 

Bromine 148 

Broml9atin 472 

Bromoform^ 367,387 

Bromo-hydi'osalicylic  acid  405 

Bromophenisic  acid  628 

Bromosamide 405 

Brown  coal 630 

Brncinc 444 

Bunsen's  battery 194 

Butter 485,  508 

of  antimony 288 

Butyl    392 

Butylene r.92,  398 

Butylic  alcohol 3st2,  395 

Butyric  acid 395,  465 

ether 357 

Butyrin 485 

C. 
Cacao  butter 484 

Cadet's  faming  lir;[uid 377 


Paoe 

Cadmium  274 

analytical  remarks 274 

Caffeine 460 

murexide 451 

Calamine 273 

Calcium  and  its  com- 
pounds    239 

fluoride  of 243 

analytical  remarks 244 

Calc  sinter 242 

Calculi,  biliary 487 

urinary 443,  515 

fusible 516 

mulberry 516 

Calomel 303 

Camphene 489 

Camphogen 492 

Campholene 492 

Campholic  acid 492 

Camphor 492 

artificial 489 

Camphoric  acid 492 

Camphylene 489 

Canada  balsam 494 

Cane-sugar 333 

Candle,  flame  of. 158 

Candl'^s,  stearin 488 

Canth^ridin 487 

Caoutchouc 494 

mineral 531 

tubes  (note) 129 

Caoutchoucin  ^ 494 

Capric  acid 395 

Capivi,  oil  of ."  490 

Caproic  acid 395,  485 

Caproyl 395,  488 

Caprylicacid 395,  488 

alwhol 396,488 

Caramel 334 

Carbamide 437 

Carbazotic  acid 473 

Carbides  of  hydi-ogen 153 

Carbolic  acid 526 

Carbon  127 

chloride  of. 365 

bisulphide  of 169 

compounds   with    oxy- 
gon  .'..  128 

estimatiou    in    organic 

bodies 321 

Carbonate  of  baryta 238 

of  cttpper 278 

of  lead 280 

of  lime 241 

of  magnesia 246 

of  oxide  of  amyl 378 

of  potassa 219 

of  silver 298 

of  80<la 225 

of  zinc 273 

Carbonates 130 

analysis  of 228 

of  ammonia 233 

Carbonetted  hydrogen, 

light 163 

Carbonic  acid 129 

ether 355 

oxide 130 

Carbyl,  sulphate  of. 365 

Carlsbad,  water  of 5.38 

Carmine 477 

Carminic  acid 477 

Cartier's  hydrometer 535 

Carthamia 478 


Paoc 

Carragheen  moss 339 

Casein 498 

Cassava 339 

Cassius,  purple. 283 

Castor-oil 488 

Catechu 416,  417 

Cedar-wood,  oil  of 491 

Cedrene 491 

Cedriret 524 

Cellulose 841 

Cement 240 

Cements,  lime 240 

Cement,  Parker's  or  Ro- 
man    240 

Cerasin 340 

Cerebric  acid 517 

Cerebrolein 517 

Cerin 486 

Cerite „  251 

Cerium 251 

Cei-otate  of  oxide  of  cero- 

tyl 486 

Cerotic  acid 486 

Cerotyl 486 

Cerotylic  acid 394 

alcohol 394,486 

Cetyl-series 487 

Cetylicacid 394,486 

alcohol 394,486 

Chalk : 241 

stones 438 

Chameleon,  mineral 259 

Charcoal,  animal  and  ve- 
getable   128 

Cbelidonic  acid 447 

Chelidonium  majus 447 

Chemical  philosophy 170 

Chimneys,  action  of. 57 

Chinese  wax 486 

Chinoline 464 

Chinoidine 448 

Chloracetates 375 

Chloracetic  acid 318,  376 

Chloral 366,  370 

insoluble 366 

Chlorauile 449 

Chloraniline 460 

Chlorate  of  potassa 221 

Chloretheral 367 

Chlorhydric  acid 141 

Chloric  acid 145 

Chloride  of  aluminium...  248 

of  ammonium 233 

of  amyl 389 

of  antimony .*. 288 

of  arsenic 292 

of  barium 237 

of  benzoyl 399 

of  boron 169 

of  calcium 240 

of  chromium 2ij8 

of  cinnamyl 408 

of  copper 278 

of  cyanogen 430 

of  ethyl 853 

of  gold 300 

of  hydrocarbon 155 

of  iodine 168 

of  kakodyl 378 

of  lime 243 

of  magnesium 245 

of  methyl 382 

of  mercury 304 

of  nitrfgen  1C7 


INDEX. 


647 


Chloridk  —  cont  Page 

of  olefiantgas 363 

of  phenyl  527 

of  phoi»phoru8 ^...  168 

of  platinum 308 

of  potassium 223 

of  silicium 169 

of  silver 298 

of  sodium 231 

of  sulphur 168 

of  zinc 273 

Chlorides  of  carbon.,  365,  366 

Chloriue 139 

compounds  with 143 

estimation  of,  inorganic 

bodies 328 

peroxide  of. 144 

Chlorisatin 472 

Chlorobcnzol  399 

Clilorobenzide  399 

Chloro-carbouic  acid 131 

ether 3.57 

Chlorochromic  acid 269 

Chlorocinnose 408 

Chloroform 366,  386 

Chloro-hydro-salicy  lie  acid  405 

Chloro-hyponitric'acid 143 

Chlorokiuoue 449 

Chlororaetry 244 

Chloroniceic  acid 463 

Chloronicene 463 

Chloronioine 463 

Chloro-nitrous  acid 143 

Chloro-phenisic  acid 527 

Chloro-phenusic  acid 528 

Chloro-naphthalic  acid.».  530 

Chloropicrin 473,  479 

Chloro-salisenin 406 

Chlorosamide  405 

Chloro-sulph  uric  acid  136,  364 

Chlorous  acid 144 

Chlorovalerisic  acid 393 

Chlorovalerosic  acid 393 

Cholesterin 487 

Cholestrophane 450 

Cholic  acid 510 

Choloidinic  acid 511 

Chondrin 600 

Chromate  of  lead -267 

of  potassa 268 

Chrome-yellow 269 

Chromic  add 268 

Chromium  267 

analytical  remarks 268 

Chrysammic  acid 479 

Chrysaiiilic  acid 459 

Chrysen  525 

Chrysolepic  acid 479 

Chrysolite 247 

Chrysophanic  acid 476 

Chyle 607 

Cinchonine  447 

Cinchovatine 448 

Cinnabar 301,  300 

Cinnamein  408 

Cinnamic  acid 407 

Cinnamol 408,  495 

Cinnamon,  oil  of. 407 

Cinnamyl    and   its    com- 
pounds   407 

Circular    polarization  of 

light 76 

Circulation  of  the  blood..  503 
Citraeouic  acid 4U 


Page 

Citrates 414 

Citric  acid 413 

Clarifying  wines  and  beer  502 

Clay  iron-stone 2C3 

origin  of 249 

Cleavage 203 

Coal,  brown 530 

gas 155 

Cobalt 271 

analytical  remarks  on..  272 

cyanide  of 426 

acetate  of 374 

Cobalto-cyanogen 433 

Cobalt-ultramarine 272 

Cocculus  indicus 452 

Coccus  cacti 477 

Cochineal 477 

Cocinic  acid 484 

Cocoa-oil 484 

Codeine 446 

Cohesion 184 

Coke 128 

Colchicine , 460 

Collodion 344 

Colophene 490 

Colophony 493 

Colouring  principles,  org.  470 

Columbium 286 

Combination  by  volume..  177 

by  weight 172 

Combining  quantities  174, 176 

Combustion 156 

Comenicacid 447 

Common  salt 231 

Compass,  mariner's 89 

Combination,  laws  of. 172 

Conci'etions,  gouty 438 

Condensation  of  gases  and 

vapours 61,  62 

Conduction  of  heat 52 

Conicine 450 

Conine 450 

Constant  battery 193 

Cotarniue  446 

Copaiba  balsam 494 

Copal 494 

Copper 277 

acetates  of 375 

alloys  of. 278 

analytical  remarks  on..  278 

ferrocyanide  of 433 

•  salicyiide  of 404 

Cork 484 

Corn-oil 383 

Corundum 248 

Corrosive  sublimate 304 

Cream  of  tartar 411 

Croconic  acid 345 

Crown-glass 252 

Crucibles 255 

Cryophorus 65 

Cry.^tals 202 

Crystallization 202 

Crystalline  forms 202 

Crystallization,  water  of..  202 

phenomena  of 202 

Cube 206 

Cubebs,  oil  of 490 

Cudbear 474 

Cumaric  acid 407 

Cumarin 406 

Cumic  acid 403,  491 

Cumidine 4G2 


Paoi 

Cumin  oil 491    ~^ 

Cuminol 403,  491 

Cumol 403,462,492 

Curarine 451 

Curd 499 

Cyanates 427 

Cyanethine,, 354 

Cyamelide 428 

Cyanic  acid ^  426 

Cyanide  of  amyl 389 

of  benzol 400 

of  ethyl 354 

of  hydrogen 420 

of  kakodyl 379 

of  methyl 383 

of  phenyl 527 

Cyanides ^ 424 

Cyaniline 460 

Cyanite 260       m 

Cyanogen 420 

bromide  of. 4^ftiM 

chloride  of. 430 "^^ 

compounds  and  derivar 

tives 420 

iodide  of. 430 

Cyanuric  acid 426,  427 

Cymol 403,  491 

Cystic  oxide 443,516 

D. 

Dammar  resin 494 

Daniell's  battery 193 

Dutch  liquid 155,  318,  363 

Datura  stramonium 451 

Daturine 451 

Daphne  mezereum. 452 

Daphnin 452 

Decay 320 

Declination,  magnetic 88 

Decolorization  by  charcoal  128 

Deliquescence „  202 

Delphinic  acid 485 

Delphinine 451 

Delphinium  staphisagria  451 
Dew,  origin  and  cause  of     81 

Density 27 

Density  of  vapours,  deter- 
mination of 330 

Dextrin 338 

Dextro-racemic  acid 413 

Diabetes 335,  514 

insipidus,  sugar  from...  338 

Dialuric  acid 442 

Diamagnetic  bodies 89 

Diamond „  127 

Diastase 339 

Diathermancy  82 

Didymium 251 

Diffusion 112 

false 507 

Digestion 521 

Dimorphism 203 

Dippel's  oil 465 

Disacryle 487 

Disinfection 141,244 

Disinfecting   solution  of 

Labarraque 24." 

Disposing  influence 186 

Distillation 58 

dry  or  destructive 319 

Dithionic  acid 135 

1  ode  ahedron 208 

D<n.ble  salts 202 


548 


INDEX 


Page 

Draconic  add 491 

Dragons'  blood 494 

Dropsy,  fluid  of. 508 

Dyes,  red  and  yellow 477 

Dyeing,  action  of. 470 

Dyslysin 511 

E. 

Earthenware 254,  255 

Eblanin 388 

Ebullition 54 

Effervescing  draughts 411 

Efflorescence 202 

Eger,  water  of. 539 

Egg,  white  of 496 

Elaidic  acid 484 

Elaidia 484 

Elain 480 

Elais  guianensis 483 

Elaldohyde 370 

Elaterin 452 

Electric  eel 99 

Electric  machine 94 

Electrical  current 97 

Electricity 92 

Electro-chemical  decompo- 
sition   187 

Electrodes 187 

Electrolysis 187 

Electro-magnetism 100 

Electrophorus 97 

Electro-plating 195 

Electrolytes 187 

Electrotype 194 

Elementary  bodies 103 

substances,  table  of 176 

substances,  table  of  sym- 
bols   180 

Elements 104 

Elemi,  oil  of. 490 

Ellagic  acid 418 

Emerald 251 

Emery 248 

Emetine 451 

Ems,  water  of 538 

Emulsin 422 

Epsom  salt 246 

Equator,  magnetic 89 

Equisetic  acid.  413 

Equisetum,  acid  of 414 

Equivalents,  table  of. 176 

volume 178 

law  of. 174 

Erbium 251 

Eramacausis.... 320 

Erytrarsin 379 

Erythric  acid 474 

Erythroprotide 500 

E.«sence'of  turpentin 489 

Essential  oils 488 

Ethalic  acid 486 

alcohol 486 

Ether 351 

acetic 356 

acetic,  chlorinetted 367 

boracic 3.55 

butyric 3.57 

carbonic 355 

chlorocarbonic —  357 

cyanic 428 

cyanuric 428 

formation  of 360 

formic 856 

farmic,  chlorinetted 36'' 


Ether— co?i<.  Page 

hydriodic  353 

hydrobromic 353 

light  hydrochloric 363 

margaric 357 

muriatic,  heavy 367 

nitric 354 

nitrous „  855 

cenanthic 357 

oxalic 356 

oxamic 356 

phosphoric 354,  359 

preparation  of 360 

silicic 355 

sulphuric 354 

sulphurous 854 

valerianic 857 

Etherin 362 

Etherole 362 

Ethers,  compound 352 

of  fatty  acids 357 

Ethionic  acid 366 

Ethyl 352 

bromide  of. 353 

chloride  of. 853 

cyanide  of, 354 

iodide  of. 353 

oxide  of 851 

oxide  of,  compounds  of, 
with  acids,  see  Ether.  351 

oxide  of,  cyanate  of 428 

oxide  of,  cyanurate  of...  428 

-series,  ba.ses  of 455 

sulphide  of. 354 

-theory 352 

-zinc  368 

Ethylamine 455 

-urea 456 

Ethylamylaniline 464 

Ethyl-ammonia 455 

Ethylauiline 463 

Ethylene 362 

Ethylophenylamine 464 

Ethylo-toluidine 464 

Ethyl-oxamide 455 

Euchlorine 145 

Euchrone 345 

Euchronic  acid 345 

Eudiometer 116,  122 

Euclase 250 

Eupion 523 

Euxanthicacid 479 

Euxanthone 479 

Evaporation 59 

Evernic  acid 475 

Everninic  acid 476 

Evernia  pruna.stri 475 

Expansion  by  heat 41 

of  fluids 46 

of  gases 48 

of  solids 44 

F. 

Fachingen,  wat«r  of 540 

Fats 480 

Fatty  acids 395 

Fecula 3.37 

Felspar 249 

Fennel-oil 491 

Fermentation 345 

butyric 349 

lactic 349 

vinous 346 

visPX)U8 351 

Fermei'tfi..      345 


Paob 

Ferricyanide  of  hydrogen  433 

Ferricyanides 433 

Ferricyanogen 433 

Ferridcj'anogen 433 

Ferrocyanides 426,  431,  433 

Ferrocyanogen 430 

Fibrin 497 

Fire,  bhie 290 

damp  153 

red  and  green 239 

Flame,  structure  of. 156 

Flint-glass 252 

Florence  flasks 125 

Fl uids,  expansion  of 46 

Fluoride  of  boron 152 

of  calcium 243 

of  silicium  150 

Fluorine 149 

Fluor-spar 243 

Food 518 

Formates 386 

Formic  acid 385,395 

ether 350 

Formo-benzoic  acid 400 

Formo-methylal 387 

FormulsB 329 

empirical 32D 

rational 329 

French  weights  and  mea- 
sures   542 

Frigorific  mixtures 53 

Fruit-sugar 335 

Fucusamide 466 

Fucusine 466 

Fucusol 466 

Fulminates 428 

Fulminating  silver  of  Ber- 

thollet 299 

Fulminic  acid 428 

Fumaramide 416 

Fumaric  acid 416 

Furfurine 465 

Furfurolamide 466 

Furfurol 465 

Furnace,  reverberatory...  157 

Fusel-oil 388 

of  grain-spirit 393 

Fusible  metal 275 

Fustic  wood 479 

G. 

Gadolinite 251 

Galena 279 

Gallates 418 

Gallic  acid 416,418 

Galls,  nut 417 

Galvanism 97 

Galvanometer 83 

Galvanoscope 83,101 

Garancin 478 

Garlic,  oil  of. 493 

Garnets 251 

Gas,  coal  and  oil 155 

olefiant 154 

Ga-ses,  diffusion  of. 112 

expansion  of 48 

management  of 106.  Ill 

122,  129,  132 
physical  constitution  of     34 

specitJc  heat  of 67 

Gas-holder 107 

Gastric  juice 521 

Qaultheria    procumbens, 
oil  of 403 


INDEX, 


649 


Page 

Gelatin 500 

-sugar 501 

Gentiauin 451 

German  silver ^ 271 

Geyser  springs  of  Iceland  11S^ 

Gilding 301 

Glass,  coloured 253 

manufacture  of. 252 

variety  of 252 

soluble 254 

Glauber's  salt 229 

Gliadin 519 

Globulin 504 

Glucic  acid 330 

Glucinum 252 

Glucose 334 

Glue 502 

Gluten 337,  519 

Glutin 337 

Glycerin 481,  483 

Glvco-benzoic  acid 402 

Glyeocine 402,  501 

Glycocoll 501 

Glyco-cholalic  acid 510 

Glyco-byocholalic  acid 512 

Glycolamide 402 

Glycolic  acid 402,  501 

Glycyrrhizin 336 

Goniometry 204 

Gold,  analytical  remarks.  300 

and  its  compounds 299 

cyanide  of. 42C 

-dust 299 

-leaf 300 

standard  of  England....  299 

Goulard  water 374 

Gouty  concretions 4;5S 

Gramme 542 

Grape  sugar 334 

Graphite 128 

Grass  oil 490 

Gravitj',  specific 27 

Greenheart  timber 451 

Greeu  fire 239 

G  reen  salt  of  M  agnua 309 

Groups,  isomorphous 211 

Grove's  battery 194 

Guanine 443 

Guano 443 

Gum 340 

arable 340 

benzoin 495 

British 339 

of  cherry-tree 340 

tragacauth 340 

Gun  cotton 344 

Gun  metal 27 

Gunpowder 220 

Gutta  percha '.  494 

Gypsum 241 

II. 

Hahnemann's  soluble 

mercury..  303 

Ilaiitus 504 

Haloid  salts 201 

Hardness  of  water 241 

permanent 241 

temporary 242 

Ilarmaline 450 

Harmine 450 

Hiuchetin W6l 


Heat  —  cont.  Page 

animal 507 

capacity  for  specific 66 

conduction  of 52 

latent 53 

phenomena  of. 41 

radiation 79 

reflection 79 

transmission 82 

Heavy  spar 238 

Holicin 406 

Helicoidin ' 

Hemihedral  crystals 209 

Hemipinic  acid 446 

Hematite 261 

Ilematosin 504 

Hematoxylin..^ 479 

Hepar  sulphuris 222 

Herrings,  liquor  of  salt....  458 

Ile.speridJn 452 

Heulandite 251 

Hippuric  acid 402 

Homologous,  term 396 

Uomologues  of  aniline....  462 

of  benzol 4G2 

of  the  glj'cocine-series...  501 

of  the  salicyl-series 491 

Houeystone 345 

Hop 348 

oil  of. 490 

Hornebleude 247 

Horn  silver 298 

Horse-radish,  oil  of. ,  493 

Iluano 443 

Humic  acid 336 

Humus 336 

Hydrate  of  oil  of  turpen- 

tin 489 

Hydrates,  term 118 

Hydride  of  anisyl 490 

Hydride  of  benzoyl 396 

Hydride  of  cinnamyl 407 

Hydriodic  acid 147 

ether 353 

Hydrobenzamide 400 

Hydrobroniic  acid 148 

ether 3.53 

Hydrocarbon,  chloride  of  155 

Hydrochloric  acid 141 

ether,  heavy 367 

Hydrocyanic  acid 420 

Hydroferricyanic  acid 433 

Ilydroferrocyanic  acid 430 

Hydrofluoric  add 149 

Hydrofluosilicic  acid 150 

Hydrogen 110 

antimonetted 289 

arsenetted 292 

binoxideof. 115,  119 

carbides  of 153 

carbonetted 153 

estimation    in    organic 

bodie.'? 321 

pcrsulphide 165 

pho.sphoretted 166 

selenietted 165 

sulphuretted 161 

Ilydrokinone,  colourless..  448 

green  ,.  448 

Hydroleic  acid 487 

Hydromargaric  acid 487 

Hvflromargaritic  acid 487 

Hydrometer  tables 634 


lieat,  absorption 80  i  Hydrosahcylic  acid 404 


Paqk 

Hydrosulphocyanic  acid..  435 

Hydrosulphuric  acid 163 

Hygrometer,  dew-point...     66 

wet-bulb 62 

Hyocholalic  acid 512 

Hyocholic  acid 511 

Hyoscyamine 451 

Ilyoscyamus  niger 457 

Hyodyslysin 512 

Hypochloric  acid 144 

Hypochlorous  acid 144 

Hyponitric  acid 126 

Hypophosphoz'ous  acid....  138 
Hyposulphale  of  silver...  29S 

Hyposulphate  of  soda 229 

Hyposulphite  of  silver....  298 

Hyposulphites 135 

Hyposulphobenzic  acid...  398 

Hyposulphuric  acid 135 

bi.sulphuretted 135 

sulphuretted 135 

trisulphuretted 136 

Ilyposulphurous  acid 135 


Iceland  moss 239 

Idrialin 5-32 

Imidogen-bases 454 

Inclination,  magnetic 88 

Incrustations  in  boilers..  242 

Indian  yellow 479 

Indigo 470 

red 470 

vat 240 

white,  or  de-oxidized....  471 

Inrlin 472 

Indinic  acid 472 

Tnosinic  acid 503 

Inosite 503 

Ink,  label 494 

blue,  sympathetic 271 

Inulin 239 

Iodic  acid 147 

Iodide  of  amyl 388 

of  arsenic 292 

of  benzoyl 400 

of  cyanogen 430 

of  ethyl  353 

of  kakodyl 379 

of  mercury 305 

of  methyl 383 

of  nitrogen 167 

of  silver 299 

Iodine 146 

chloride  of. 168 

Iodoform  387 

lodo-Pulphuric  acid 136 

Ipecacuanha .'•  451 

Iridium 312 

Iron,  acetate  of. 374 

analytical  remarks  on..  263 

and  its  compounds 259 

cyanide  of. 42G 

manufacture  of. 263 

protoxide,  lactate  of.....  351 
sesquioxide,benzoateof  397 

Isatin 471 

Isatinic  acid 472 

Isatyde 472 

Isethionic  acid 36G 

Isinglass 500 

Ipomeric  bodie? 318 

IbOmorphiBm..:..-   . 20ll 


5d0 


INDEX. 


Pagk 

Isomorphous 209 

Ilaconic  acid 414 

J. 

Jade 247 

Japonic  acid 418 

Jet 530 

Jew's  pitch 631 

Juice,  gastric 521 

Juniper,  oil  of. 490 

K. 

Kakodyl 377 

-compounds 377 

Kakodylic  acid 379 

Kalisaccharic  acid 336 

Kaolin 255 

Kapnomor 624 

Katalysis 186,  345 

Kelp 146 

Kermes  mineral 2S9 

Kinic  acid 447,  448 

Kino 416 

Kinone 448 

Kish 128 

Kissingen,  Ragozi  water..  539 

Kreatin 602 

Kreatinine 450,  502 

Kreosote 524 

Kreuznach 541 

Kyanol 465 

Kyan's  method  of  preserv- 
ing timber. 305 

L. 

Labarraque's  disinfecting 

fluid 243 

Label  ink 494 

Lac 494 

Lactamide 3.5o 

Lactates 350 

Lactic  acid 349 

Lactide 350 

Lactin 336 

Lactone 350 

Lake 470 

Lamp,  argand 1.59 

flame  of. 159 

safety IGl 

spirit 159 

without  flame 371 

Lampblack 128 

Land    and    sea   breezes, 

cause..^ 81 

Lanthanium 251 

Laughing-gas 125 

l.numonite 250 

Laurel  oil 490 

Luvender,  oil  of. 492 

Lead 279 

acetates  of 374 

ailoj's  of. 281 

analytical  remarks  on.^  281 

benzoateof 397 

binoxide  of. 279 

malate  of. 415 

-plaster 483 

protoxide  of. 279 

red 279 

sugar  of. 374 

•tree 195 

white 280 

Leaven 349 

lie'^noraparella 470 


Lecanora  —  cont.  Pa^p. 

tartarea 476 

Lecanoric  acid 474,  475 

Legumin 520 

Lemons 413 

oil  of 490 

Leucine 500 

Leucoline 464 

Leukol 465 

Levo-racemic  acid 413 

Leydenjar 96 

Lichens 474 

Light 71 

blue  or  Bengal 290 

chemical  rays  of .".    77 

polarized 75 

Lightning  ro4s 97 

Lignin 341 

Lignite 530 

Lignone 388 

Lime 2:^9 

acetate  of „  373 

aconitate  of 414 

analytical  remarl*;? 244 

benzoateof. 397 

carbonate  of. 241 

chloride  of. 243 

lactate  of. 351 

malate  of. 415 

oxalate  of. 343 

phosphates  of. 242 

tartrate  of. 411 

Limestone 241 

Liquefaction  of  gases 62 

Liquor  ammoniae 162 

amnii 508 

Liquorice  sugar 336 

Litharge 279 

Lithia 235 

Lithicacid 4.38 

Lithium 235 

Lithofellinic  acid 512 

Litmus 474 

Loadstone 8,  261 

Loaf  sugar 334 

Logwood 478 

Lupulin 348 

Lungs 506 

Lymph 507 

M. 

Madder 477 

Magnesia 245 

acetate  of 373 

aconitate  of 414 

alba 246 

analytical  remarks  on..  247 

carbonate  of 246 

pho.sphate  of. 246 

silicates  of 247 

sulphate  of. 246 

tartrate  of. 411 

Magnesium 245 

chloride  of 245 

Magnetism 86 

Magnus,  green  salt  of. 309 

Malachite 278 

Malamic  acid 415 

Malamide 415 

>IalAtes 415 

Maleicacid 416 

Malic  acid 414 

Malleability  of  metals 198 

Malting 34S 


Tagjs 

Manganese,  acetate  of. 374 

and  its  compounds 256 

assay  of. 257 

Manna  sugar 337 

Mannite 3:57 

Manures 5'J2 

Maple,  sugar  from 334 

Marble 241 

artificial  coloured 241 

]VTarc-brandy,  fusel-oil  of..  393 

Margaric  acid 481 

ether .357 

Margarin 480,  4^1 

Margarone 482 

Marienbad,  water  of 539 

Mariotte's  law 38 

Marsh  gas 153 

Marsh  mallow 452 

Marls 250 

Massicot 279 

Mastic 494 

Meadow-sweet,  oil  of. 404 

Measures 642 

Meat 518 

Meconic  acid 446 

Meconine 446 

Meerschaum 247 

Melam 436 

Melamine 436 

Melaniline 461 

Melanic  acid 404 

Melasinic  acid 336 

Melis.sic  acid 394 

alcohol 394,486 

Mellite 345 

Mellitic  acid 345 

Mellon 435 

Membranous  tissues 516 

Membranes,  mucous 508 

Mercaptan 367 

methyl- 387 

Mercury ■„...  301 

acetates  of. 375 

analytical  remarks  on...  306 

cyanide  of 425 

fulminate  of 429 

its  compounds... 302 

Meridian,  magnetic 88 

Me.Mtilol 376 

Me.'iityl 376 

Mesotype 250 

Mesoxalic  acid 440 

Metacetone 376 

Metacetonic  acid 376 

Metaldehyde 370 

Metagallic  acid '  419 

Metals 197- 

classification 216 

Metamargaric  aeid 487 

Metapectin 340 

Metapectic  acid „.  340 

Metaphosphoric  acid 213 

Metastyrol 495 

Meteorites 259 

Methionic  acid 366 

Methyl 381 

Methylamine 457 

-urea 457 

Methyl-ammonia 457 

Methvl-compounds...  381.382 

Methyl-pther '  3S2 

Methyl-ethyl-amylamino.  4f4 
-urea 457 


INDEX 


551 


Page 
Blethyl  -  ethyl  -  amylophe- 
nvlammonium,  oxide 

of 464 

Metbyl-mercaptan 3S7 

Methylo-biethyl-amyl-am- 

monium,  oxide  of 464 

Methyl-salicylateof,  oxide 

of 491 

Methyl-series,  bases  of  the  457 

Metoleic  acid 487 

Metre 542 

Mica 250 

Slicrocosmic  salt 230 

Milk 508 

spirit  from 509 

Milk-sugar 336 

Miudererus,  spirit  of. 373 

Mineral  chameleon 259 

waters,  table  of. 638 

Molasses 334 

Molecular  actions 184 

Molybdenum 284 

Momordica  daterium 452 

Monobasic  acids 212 

Mordant 283 

Mordants 470 

Morphia 444 

Morphine 444 

Mortar 240 

Mosaic  gold 283 

Mucic  acid 344 

Mucilage 340 

Mucx)us  membranes 508 

Mucus 508 

Mulberry  calculus 616 

Multiple  proportions 173 

Multiplier 83 

Murexan 443 

Murexide 442 

caffein 450 

Muriatic  acid 141 

ether,  heavy 367 

Muscovado  sugar 334 

Mushroom  sugar 337 

Must 347 

Mustard,  oil  of 492 

bases  from  the  oil  of....  466 

Mykomelinic  acid 440 

Myricin 492 

Myristicacid 484 

Myi-istica  moschata 484 

Myronic  acid 493 

N. 

Naphtha 531 

Naphthalidine 462 

Naphthalin 462,  529 

Narc«ine 446 

Narcogenine 446 

Narcotine 445 

Kepheline 250 

Nervous  substance 51 

Neutrality  of  salts 200 

Neutralization 176 

Nickel 269 

acetate  of. 374 

analytical  remarks 271 

Nicotine 450,  469 

Niobium  286 

Nitraniline 460 

Nitranisic  acid 490 

Nitraniside 490 

Nitrate  of  ammonia 234 


Nitrate  —  cont.  Page 

of  baryta 238 

of  bismuth 275 

of  lead... 280 

of  oxide  of  methyl 384 

of  potassa 220 

of  soda 230 

of  silver 298 

Nitrates 124 

of  mercury 302 

Nitre 220 

cubic 230 

sweet  spirits  of. 355 

Nitric  acid 123 

acid,  fuming 126 

ether 354 

oxide 126 

Nitrile-bases 455 

Nitro-benzamide 462 

Nitro-benzoic  acid 397 

Nitro-benzol 399,462 

Nitro-chlorouicene 463 

Nitro-ooccusic  acid 477 

Nitro-cumic  acid 403 

Nitro-cumol 462 

Nitrogen 120 

binoxide  of. 126 

chloride  of. 167 

compounds  with  oxygen  122 
estimation    in   organic 

bodies 324 

iodide  of 167 

Nitro-naphthalase 462 

Nitro-phenasic  acid 528 

Nitro-phenesic  acid 528 

Nitro-phenisic  acid 528 

Nitro-prussides 433 

Nitro-salicylamide  492 

Nitro-salicylic  acid  ...  406,  473 

Nitro-toluol 402,495 

Nitro-toluylic  acid 403 

Nitrous  acid 126 

ether 355 

oxide 125 

Nitro-xylol 462 

Nomenclature 170 

Norium 352 

Notation,  chemical 180 

Nutgalls 417 

Nutrition,    plastic    ele- 
ments of 520 

0. 

Octahedron 206 

(Enanthic  acid. 357 

ether 357 

CEnanthylicacid 395 

Oil  gas 155 

of  alliaria  officinalis 493 

of  aniseed 490 

of  assafoetida 493 

of  badian 491 

of  bergamot 490 

of  bitter  almonds 396 

of  bitter  fennel 491 

of  capivi 490 

of  cedar  wood 491 

of  cinnamon 407 

of  elemi 490 

of  cubebs 490 

of  cumin 491 

of  garlic 493 

of  gaultheria  procum- 
bens 406,  491 


Oih— cont.  Paos 

of  Guiana-laurel 490 

of  hops 490 

of  horseradish 493 

of  juniper 490 

of  lavender 492 

of  lemons ,  490 

of  meadow-sweet 404 

of  mustard 492 

of  onions 49.3 

of  orange  flowers 492 

of  orange  peel 490 

of  pepper 490 

of  peppermint 492 

of  rosemary 492 

of  rose  petals 492 

of  spiraea  nlmaria 404 

ofturpentin 489 

of  valerian 492 

of  vitriol 134 

of  wine,  heavy  and  light  362 

of  wintergreen 491 

Oils 480 

drying  or  non-drying...  480 

volatile 488 

Olefiant  gas 154 

and  its  compounds 362 

Oleic  acid 482 

Olein 480,  482 

Olive  oil 488 

Onions,  oil  of. 493 

Opiammon 445 

Opianic  acid 445 

Opianine 446 

Opium 444 

Orange  flowers,  oil  of 492 

oil  of -peel 490 

Orcein 476 

Orcin 474,  476 

Organic  baijes 444 

bases,  artificial 453 

substances,   action    of 

heat  on 319 

substances,   classifica- 
tion   319 

substances,  composition 

elementary 318 

substances,  decomposi- 
tion of. 319 

substances,    ultimate 

analysis  of. 320 

Orpiment 292 

Orsellinic  acid 474,475 

Osmium 314 

Oxalate  of  oxide  of  methyl  384 

Oxalates 342 

Oxalic  acid 341 

ether 356 

Oxalo-nitrilc.i 4G1 

Oxalo-vinic  acid 359 

Oxaluric  acid 440 

Oxamethane ••....    356 

Oxamethylane 384 

Oxamic  acid 343 

ether 358 

Oxamide 343 

Oxanilic  acid 461 

Oxanilide 461 

Oxide,  cystic 443 

ofallyl *93 

of  amyl,  bydrated 388 

of  benzoyl 896 

of  bismuth 275 

of  copper 227 


552 


INDEX 


Oxinn  —  cont.  Page 

of  kakodyl 377 

o1  methyl 882 

of  methyl,  hydrated....  381 
xanthic 443 

Oxides 109 

of  antimony 288 

of  chromium 267 

of  gold 300 

of  hydrogen 115 

of  mercury 302 

of  platinum 308 

of  potassium 218 

of  silver 297 

of  sodium 224 

of  zinc 273 

Oxygen 105 

-adds 201 

Oxy-hydrogen,  flame  and 

blowpipe 113 

safety-jet 161 

Oxy-salts 201 

Ozone 110 

P. 

Palladium,  cyanide  of  311, 426 
Palmilate  of  oxide  of  me- 

lissyl 486 

Palmitin 485 

Palmitic  acid 485 

Palm-oil 484 

Papaverine 446 

Parabanic  acid 440 

Paracvanogen 420 

Paraffin 623 

Parakakodylic  oxide 

Paramagnetic  bodies 89 

Paramide 345 

Paramorphine 446 

Paramylene 390 

Paranaphthalin 530 

Parapectin 340 

Paratartaric  acid 413 

Parellic  acid 470 

Parmelia  parietina 476 

Pear,  flavour  of 389 

Pearlash 219 

Pectic  acid 340 

Pectin 340 

Pelargonic  acid 357,  395 

Pelopium 286 

Pentathjonic  acid 136 

Popper,  oil  of 490 

Peppermint,  oil  of. 492 

Pepsin 521 

Perclilorato  of  potassa  ...  222 

Porch loric  acid 145 

Pori'USRion-caps 429 

I'eriodic  acid 148 

IVroxide  of  chlorine 144 

I'ersulphide  of  hydrogen.  KiS 

Peru  balsam 408 

J'eruvin 408 

Pctalite 250 

Potinine 405 

F'ettcukofer's  bile-test 511 

Petroleum 531 

Petrolene 5ol 

Petuntze 255 

Piienetol 527 

I'heuol 491,526 

Phenyl 524 

alcohol 459,  .^27 

benzcate-'f 527 


PHENTL  —  COT?/.  Pagk 

chlorid«of. 527 

cyanide  of 527 

hydrated  oxide 520 

.  series,  bases  of — 459 

Phenyl-amine 469 

Philosophy,  chemical 170 

Phloretin 406 

Phloridzin 406 

Phocenic  acid 485 

Phorone 492 

Phosgene  gas 131 

Phosphate  of  lime 241 

Phosphate  of  magnesia...  246 
of  magnesia  and  ammo- 
nia   246 

Phosphate  of  soda 2.30 

Phosphethylic  acid 359 

Phosphide  of  calcium 241 

Phosphobiethylic  add 359 

Phosphoretted  hydrogen.  166 

Phosphoric  acid 1'58 

acid,  anhj'drous 213 

add,  bibasic 213 

acid,  glacial 213 

acid,  monobasic 213 

acid,  tribasio 212 

ether  354,3-59 

Phosphorous  add 138 

Phosphorus 137 

-bases 468 

chloride  of  168 

compounds  of 138 

Phosphovinic  acid 358 

Photography 77 

"Phthalic  acid 529 

Picamar 524 

Picoline 465 

Picric  acid   473,  528 

Picro-erythrin 475 

Picrotoxin 452 

Pimaric  add 494 

Pinic  add 493 

Piperine 451 

Pitch 623 

mineral 531 

Pit-coal 530 

Plants,  supply  of  carbon 

to 130 

Plaster  of  Paris 241 

Plate  glass 252 

Platinum   and  its  com- 
pounds   307 

analytical  remarks 310 

bases 309 

Wack 307 

surface-action  of....  114,  115 

Plumbago 128 

Polarity,  magnetic 86 

Polyba^c  acids 


212 


452 
254 
250 
446 


Ponlil  or  puntil 253 

Populin 

j  Porcelain 

I     clay 

Porphyroxine 

Potash 21S 

crude 219 

Potassa 218 

I     acetate  of 373 

alum 249 

analytical  remarks  on..  224 

I      lienzoate  of ,.  397 

bicarbonate  of. 220 

I     bisulphide  of 221 


PoTA?sA  — ^on^  Paoh 

carbonate  of 219 

chlorate  of. 221 

cyanate  of. 426 

nitrate  of. 220 

oxalate  of 342 

perehlorate  of. 222 

sulphate  of 221 

tartrates  of. 411 

urate  of 438 

Potassium  and  its  com- 
pounds   217 

bromide  of. 224 

chloride  of 223 

cyanide  of 424 

ferricyanideof. 431 

ferrocyauide  of. 433 

salicylide  of. 404 

sulphides  of 222 

sulphocyanide  of. 434 

Potato-oil 488 

Precipitate,  white 305 

Prehnite 250 

Proof-spirit 347 

Propione. 376 

Propionic  acid 376,  395 

Proportionals 174 

Proportions,  multiple 173 

Propylene 388 

Protein 499 

binoxideof. 500 

teroxide  of 500 

Protide 500 

Protochloride  of  tin 283 

Protoxide  of  tin 382 

Prussian  blue 432,433 

Prussiate  of  potash,  red...  433 

yellow 431 

Prussic  acid 420 

Pscudo-erythrin 475 

Pseudo-morphine 446 

Pudding 265 

Pii  Una,  water  of. 541 

Purple  of  Cassius 283 

Purpurate  of  ammonia...  442 

Purpuric  acid 442 

Purpurin 478 

Purree 479 

Purreic  acid 479 

Purrenone 479 

Pus 508 

Putrefadion 320 

Putty  powder 2^2 

Pyrites 262 

Pyrniont,  water  of 540 

Pyroacetic  spirit 376 

Pyro-adds 319 

Pyrobeuzolin 4li6 

Pyrogallic  acid 419 

Pyrogen  acids 419 

Pyromeconic  acid 447 

Pyi'omucic  acid 34-') 

Pyrophorus  of  Ilomberg..  249 

Pyrophosphoric  add 213 

Pyrotartaric  acid 413 

Pyroxy  lie  spirit 3S1 

Pyroxylin 344 

Q. 

Quercitron  bark 479 

Quicksilver 301 

Qnina 447 

Quinidine 448 

j  Quinine 447 


INDEX 


55a 


Page 

Quinine,  amorphous 448 

Quiaoliue 464 

Quinoidine 448 


R. 

Uadiation  of  heat 

Kacemlc  acid 

Realgar 

Red  dyes 

Red  fire 

Red  lead -. 

Reflection  of  heat 

of  light 

Refraction,  double 

of  light 

Rennet 

Resins 

Respiration « 

elements  of. 

Retinic  acid ~ 

Retinite 

Reverberatory  furnace.... 

Rhodium 

Rhodizonic  acid 

Ricinoleic  acid 

Rocella  tinctoria 474, 

Rocellinin 

Rochelle  salt 

Rock  oil 

Rock  salt 

Roman  alum 

Rosemary,  oil  of 

Rubia  tinctorum 

Rubiacin 

Rubiacic  acid 

Rubian 

Rubic  acid 

Rust 

Ruthenium 


79 
413 
292 
477 
239 
279 
79 
71 
75 
72 
499 
493 
506 
506 
532 
532 
158 
312 
345 
488 
475 
475 
411 
532 
232 
249 
492 
477 
478 
478 
478 
418 
260 
314 


Saccharic  acid 343 

Saccharic  group a33 

Sacchulmic  acid 336 

Sacchulmin 336 

Safety-lamp 161 

Safflowcr 478 

Saffron 479 

Sago 339 

Saf-alembroth 305 

Sal-ammoniac 233 

Salicin 403,  452 

Salicyl  and  its  compounds  403 

hydride  of 452 

Salicylate  of  oxide  of  me- 
thyl   491 

Salicylic  acid 406 

Salicylides 404 

Salicylous  acid 404 

Saligenin 405 

Saliretin 405 

Saliva 521 

Salsola  soda 225 

Salt,  definition 109 

of  sorrel 342 

Salts,  super  or  add 202 

binary  theory  of 213 

constitution  of. 199 

double 202 

neutral 200 

Saltpetre 123,  220 

Sandarac 494 

Santonin 452 

47 


Pace 

Saponification 481 ' 

Saratoga  Congress  spring  539 

Sarcosine 503 

Saturation 176 

Schlesischer   Obersalz- 

brunnen 538 

Scheele's  green 278 

Scagliola 241 

Sea-water 118 

Sebacic  acid 484 

Seed  lac 494 

Seggars 254 

Seidchutz,  water  of. 541 

Seignette  salt 411 

Selenic  acid 136 

Selenietted  hydrogen 1C5 

Selenious  acid 136 

Selenite 241 

Selenium 136 

Seleno-cyanogen 435 

Sellers,  water  of. 541 

Serpentine 247 

Serum  of  blood 504 

Silica 150 

Silicates  of  alumina 249 

of  magnesia 247 

Silicic  ether 355 

Silicium 149 

chloride  of. 169 

fluoride  of 150 

Silver,  acetate  of. 375 

analytical  remarks 299 

benzoateof 397 

cyanide  of 426 

fulminate  of. 428 

its  compounds 296 

standard  of  England....  299 

Sikes'  hydrometer 535 

Sinapoline 467 

Sinnamine 467 

Size 502 

Shellac 494 

Skin 517 

Smce's  battery 194 

Smalt ; 272 

Soap * 481 

Soap-stone 247 

Soap-test  of  Dr.  Clark 241 

Soda,  acetate  of. 373 

alum 249 

analytical  remarks  on...  232 

ash 225 

ash,  testing  its  value....  228 

bicarbonate  of 226 

carbonate  of. 225 

hydrate  of. 224 

oxalate  of 343 

tartrates  of. 411 

urate  of. 438 

Sodium 224 

cyanide  of. 424 

ferro-cyanide  of. 4-33 

oxides  of. 224 

Solanine 450 

Solder 281 

Solids,  expansion  of. 44 

Sorrel,  salt  of. 342 

Spa  Pouhon,  water  of 540 

Spar,  calcareous 242 

Sparteine 450 

Specific  gravities  of  metals  197 
gravity  of  solids  and 
liquid." 27 


Page 

Specific  heat 66 

Speculum  metal 279 

Spectrum 74 

Speiss 269 

Spermaceti 486 

Spirit  from  milk 509 

of  Mindererus 373 

pyroxylic 381 

Spirits,  table  of  spec.  gr. 

of 537 

Spudomene 250 

Springs 118 

Starch 3.37 

State,  change  of,  by  heat..    62 

Steambath 57 

Steam  engine 57 

specific  gravity  of. n<S 

latent  heat  of. 53 

Stearic  acid 481 

Stearin 481 

candles 482,488 

Stearoptene 489 

Steatite 247 

Steel 265 

Stibethyl 369,  469 

Sticklac 494 

Slillbite » 250 

Stoneware 255 

Strontia 239 

acetate  of. 373 

tartrate  of 411 

Strontium   and  its  com- 
pounds    239 

Strychnine 449 

Styphnic  acid 479 

Styracin 408 

Styrol 408,  495 

Styrone 408 

Suberic  acid 345,  484 

Sublimate,  corrosive 304 

Sublimation 58 

Substitution,  law  of. 317 

products,  organic 317 

Succinic  acid 484 

Sugar 333 

candy 334 

copper,  test  for  the  va- 
rieties of. 335 

from  diabetes 335 

from  diabetes  insipidus  336 
from  starch  or  dextrine  338 

gelatin- 402,501 

of  lead - 374 

of  milk 336 

Sulphamylic  acid 390 

Sulphasatyde 472 

Sulphate  of  alumina 249 

of  ammonia 233 

ofbaryta 238 

of  carbyl 365 

of  copper 278 

oflime 241 

of  magnesia 246 

of  oxide  of  methyl 384 

of  potassa 221 

of  silver 298 

of  soda 229 

of  zinc 273 

Sulphates  of  mercury 303 

Sulphesatyde 472 

Sulphide  of  allyl 493 

of  amyi 390 

of  arsenic 292 


554 


INDEX. 


Sulphide  —  co7it.  PxaE 

of  barium 238 

of  benzoyl 400 

of  calcium 241 

of  ethyl 354 

of  kakodyl 379 

of  silTer...- 299 

of  sodium 231 

Sulphides 132 

of  ammonium 234 

of  antimony 289 

of  mercury 30G 

of  potassium 222 

of  tin 283 

test  for 434 

Sulphindigotic  acid 471 

Sulphindylic  acid 471 

Sulphite  of  oxide  of  ethyl  354 

Sulphites 133 

Sulphobenzide 398 

Sulphobenzoic  acid 397 

Sulphocyanide  of  allyl....  493 

Sulphocyajiides 434 

Sulphocyanogen  and  its 

compounds 434 

Sulphoglyceric  acid 483 

Sulpholeic  acid 487 

Sulphomothylic  acid  383,  384 

Sulphomargaric  acid 487 

Sulphonaphthalicacid 529 

Sulphophenic  acid 520 

Sulphosaccharic  acid 335 

Sulphotoluolic  acid 495 

Sulphovinic  acid 358 

decomposed  by  heat 359 

Sulphur 131 

acids 201 

auratum 289 

bases 201 

chloride  of. 168 

compounds  with  oxygen  132 
estimation   in   organic 

bodies 328 

salts 201 

Sulphuretted  hydrogen...  163 

Sulphuric  acid 133 

ether 354,366 

Sulphurous  acid 132 

ether 354 

Super  salts 202 

Surface -action   of  plati- 
num, charcoal,  gold, 

&c 114,  115, 128 

SylvicRcid 493 

Symbols 180 

Synthetical    method    of 

chemical  research 115 

Systems  of  crystals 206 

Synaptase 422 

T. 

Tannates 417 

Tannic  acid 416,  417 

Tannin 416,417 

Tanning 417,  517 

Tantalum 286 

Tapioca 339 

Tar 523 

mineral 531 

-oil  stearin 523 

Tartar 410 

cream  of. 411 

emetic 288,  411 

soluble 411 


P.VOE 

Tartaric  acid 410 

acid,  anhydrous. 412 

Tartralic  acid 412 

Tartrates 411 

Tartrelic  acid 412 

Tartrovinic  acid 359 

Taurin 511 

Tauro-cholalic  acid 511 

Tauro-hyo-cholalic  acid...  512 

Teeth 518 

Telluric  acid 290 

Tellurium 290 

Tellurous  acid 290 

Tension 24 

Tension  of  vapours 59 

Terbium 251 

Tereljsne ^ 490 

Terebylene 489 

Teroxide  of  protein 500 

Tetra-chloro-kinone 449 

Tetra-methyl-ammonium, 

hydrated  oxide  of 458 

Tetramyl-ammonium,  hy- 
drated oxide  of. 458 

Tetrathionic  acid 135 

Tetrethyl-ammonium,  ox- 
ide of 456 

Thebaine.' 446 

Theine 450 

Theobromine 451 

Thermo-electrical  pheno- 
mena     83 

Thermometer 42 

Thialdine 370,467 

Thionuric  acid 441 

Thio.sinnamine 406 

Thoria 252 

Thorite ; 252 

Thorium 252 

Tin 282 

analytical  remarks  on..  283 

Tinned  plate 284 

Tissue,  membranous 516 

Titanium 287 

Tolene 495 

Tolu  balsam 408,495 

Toluidine 462,  463 

Toluol 403, 462, 495 

Toluylic  acid 403 

Tonka  bean 406 

Trade  winds i 50 

Transmission  of  heat 82 

Travertin 242 

Triamylamine 458 

Triamyl-ammonia. 458 

Tribasic  acids 212 

Trichlor-aniline 460 

Trichloro-kinone 449 

Triethylamine 456 

Triethyl-ammonia 456 

Triethyl-stibin 469 

Trimethylamine 458 

Trimethyl-ammonia 458 

Trithionic  acid 135 

Trona 226 

Tungsten 284 

Turkey  red 478 

Turmeric 479 

Turnbull's  blue 433 

Turpentin 489 

common 489 

hydrated  oil  of. 490 

oil  of. 489 


TunPENTix  —  c(mL  Pag  e 

Venetian 494 

Type  metal 290 

Tyrosine 477,497 

Twaddell's  hydrometer....  535 

U. 

Ulmic  acid 336 

Ulmin 330 

Ultramarine 231 

Upas  antiar 452 

Uramile 441 

Uramilic  acid 441 

Uranium 276 

Urates 438 

Urea 427, 436 

Urethane 358 

Urethylane 384 

Uric  acid 436,  438,  515 

products  fx-om 436 

Urinary  calculi 443,  515 

Urine 512 

Urinometer 32 

Usnca  barbata 476 

Usnic  acid 476 

V. 

Valeracetonitrile 501 

Valeramide 391 

Valerianic  acid 390,492 

ether 357 

Valerian,  oil  of 492 

Valeric  acid 390,  395,  492 

Valerene 483 

Valerol 492 

Valeronitrile 391,  501 

Valyl 892 

Vanadium 285 

Vapour  of  water,  tension.  636 
Vapours,  determination  of 

.     thedensityof. 330 

maximum  density  of....     60 

tension  of. 59 

Varec 225 

Variolaria 474 

Varvicite 258 

Vegetable  acids 410 

nutrition 522 

Vegeto-alkalis 444 

Venous  blood 503 

Ventilation 51 

Veratria 449 

Veratrine 449 

Verdigris ~  374 

Verditer 278 

Vermilion 306 

Vinous  fermentation 346 

Viscous  fermentation 351 

Vitriol,  blue 278 

green 262 

oil  of 134 

oil  of,  fuming 134 

Volatile  oils 488 

Volume,  combination  by.  177 

equivalent 178 

Voltaic  battery 98 

pile,  chemistry  of  the...  187 

Voltameter 190 

Volta's  pile 98 

W. 

TTash,  distiller's 848 

Water 115 

analysis  of ~ 116 


INDEX. 


555 


Water  — oonl  Paoi! 

distilled 118 

expansion  by  heat 47 

hardness  of. 241,  242 

of  crystallization 202 

oxygenated 119 

tension  of  its  vapour....    59 

Wax -  486 

fossil 532 

Weights 542 

specific 27 

Welding 199 

Whey „ 499,  508 

White  lead 280 

precipitate 305 

Titriol 273 

Winds 50 

Wine 347 

clarifying  of. 502 

Wintergreen  oil 406 

Witherite 238 


Page 

Wolfratoium 284 

Wood  ether 382 

spirit 381 

Woody  tissue. 341 

Wootz 2P8 

Wort 348 

X. 

Xanthic  acid 3C8 

oxide 443,516 

Xanthin 478 

Xanthorrhoea  hastilis 473 

Xylidine 4C2 

Xylite 388 

Xyloidin 341 

Xylol 348 

Y. 

Yeast 346, 348 


Paob 

Yellow  dyes 477 

Yttria 251 

Yttrium 251 

Z. 

ZaflFer 272 

Zeise's   combustible    pla- 
tinum salt 365 

Zeolites 250 

Zinc 272 

analytical  remarks 273 

cyanide  of. 426 

-ethyl 368 

fulminate  of. 429 

lactate  of. 351 

Zinin's  process 479 

Zircon 252 

Zirconia 252 

Zirconium 252 


THE    END. 


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\  

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— r— 

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/ 
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DUNGLISON  (ROBLEY),  M,  D.— Medical  Lexicon;  a  Dictionary  of  Medical  Science,  con- 
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BLANCHARD  &  LEA'S  MEDICAL  PUBLICATIONS.  5 

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DAY  (GEORGE  E.),  M.  D.— A  Practical  Treatise  on  the  Domestic  Management  and  more 
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of  treating  Lumbago  and  other  forms  of  Chronic  Rheumatism.  One  volume  octavo,  2"26 
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ELLIS  (REXJA^nX),  M.D.— The  Medical  Formulart:  being  a  Collection  of  Prescriptions, 
derived  from  the  writings  and  practice  of  many  of  the  most  eminent  physicians  of  America 
and  Europe.  To;iether  with  the  usual  Dietetic  Preparations  and  Antidotes  for  Poisons. 
To  which  is  added  an  Appendix  on  the  Euderniic  u.fe  of  Medicines,  and  on  the  use  of  Ether 
and  Chloroform.  The  whole  accompanied  with  a  few  brief  Pharmaceutic  and  Medical 
Observations.  Tenth  edition,  revised  and  much  extended,  by  Robert  P.  Thomas,  M.D., 
Professor  of  Materia  Medica  in  the  Philadelphia  College  of  Pharmacy.  In  one  neat  octavo 
volume  of  296  pages. 


ERICHSEX  (JOIIX).— The  Science  and  Art  op  Surgert;  beinc:  a  Treatise  on  Surgical  Inju- 
ries, Diseases,  and  Operations.  Witli  Xotes  and  Additions  by  the  American  editor.  Illus- 
trated with  over  300  engravings  on  v/ood.  In  one  large  and  handsome  octavo  volume  of 
nearly  900  closely  printed  pages. 


FLINT  (.\USTTN),  M.  D.— Physical  Exploration  and  Diagnosis  of  Diseases  affecting  the 
Respiratory  Organs.  In  one  handsome  octavo  volume,  extra  cloth,  of  636  pages.  (Now 
Raidy.) 


FERGUSSON  (WILLI A?!),  F.  R.  S.— A  System  of  Practical  Surgery.  Fourth  American,  from 
the  third  and  enlarged  London  edition.  In  one  large  and  beautifully  printed  octavo 
volume  of  about  700  pages,  with  393  handsome  illustrations. 


FRICK  (CHARLES),  M.  D.— Renal  Affections  :  their  Diagnosis  and  Pathology.    With  Illus- 
trations.   One  volume,  royal  12mo.,  extra  cloth. 


FOWNES  (GEORGE),  Ph.  D.  —  Elementary  Chemistry,  Theoretical  and  Practical.  With 
numerous  Illustrations.  Edited,  with  Additions,  by  Robert  Bridges,  M.  D.  In  one  large 
royal  12mo.  volume,  of  over  550  pages,  with  181  wood-cuts.    Sheep,  or  extra  cloth. 


FISKE  FUND  PRIZE  ESSAYS  ON  CONSUMPTION.— By  Edvon  Lee  and  Edward  Warren, 
M.D.    In  one  neat  octavo  volume,  extra  cloth.     (Now  Ready.) 


C  BLANCHARD  &  LEA'S  MEDICAL  PUBLICATIONS. 

GRAHAM  (THOMAS),  F.  R.  S.— The  Elements  of  Inobqanic  Chemistry.  Including  the  Ap- 
plication of  the  Science  to  the  Arts.  With  numerous  illustrations.  With  Notes  and  Ad- 
ditions, by  Robert  Bridges,  M.D.,  etc.,  etc.  Second  American,  from  the  second  and  enlarged 
London  edition.    1  vol.   8vo.,  of  over  800  pages,  extra  cloth.    $4.00. 

Pakt  I.  {lately  issued),  large  Svo.,  4o0  pages,  185  illustrations.   $1.50. 

Part  II.  {now  ready),  to  match,  over  400  pages.    $2.50. 


GROSS  (SAMUEL  D.),  M.  D.— A  Practical  Treatise  on  the  Diseases,  Injuries,  and  Malfor- 
mations OF  THE  Urinary  Bladder,  the  Prostate  Gland,  and  the  Urethra.  Second  edition, 
revised  and  much  enlarged,  with  184  illustrations.  In  one  very  large  and  handsome  octavo 
volume,  of  over  900  pages,  extra  cloth  or  leather.    {Just  Isstied.) 


GROSS  (SAMUEL  D.),  M.D.— A  Practical  Treatise  on  Foreign  Bodies  in  the  Air-Passages. 
In  one  handsome  octavo  volume,  with  illustrations. 


GROSS  (SAMUEL  D.),  M.  D.  —  Elements  of  Pathological  Anatomy;  illustrated  with  three 
hundred  and  fifty  wood-cuts.  Third  and  revised  edition.  In  one  large  octavo  volume,  of 
over  900  pages,  leather. 


GROSS  (SAMUEL  D.),  M.D.— A  System  of  Surgery;  Diagnostic,  Pathological,  Therapeutic, 
and  Operative.    With  very  numerous  engravings  on  wood.    {Preparing.) 


GLUGE  (GOTTLIEB),  M.  D.— An  Atlas  op  Pathological  Histology.  Translated,  with  Notes 
and  Additions,  Ijy  Joseph  Leidy,  M.  D.,  Professor  of  Anatomy  in  the  University  of  Penn- 
sylvania. In  one  volume,  very  large  imperial  quarto,  with  320  figures,  plain  and  colored, 
on  twelve  copper-plates. 


GRIFFITH  (ROBERT  E.),  M.  D.— A  Universal  Formulary,  containing  the  methods  of  Pre- 
paring and  Administering  Officinal  and  other  Medicines.  The  Avhole  adapted  to  Physicians 
and  Pharmaceutists.  Second  edition,  thoroughly  revised,  with  numerous  Additions,  by 
Robert  P.  Thomas,  M.  D.,  Professor  of  Materia  Medica  in  the  Philadelphia  College  of  Phar- 
macy.   In  one  large  and  handsome  octavo  volume  of  over  600  pages,  double  columns. 


GRIFFITH  (ROBERT  E.),  M. D.  —  Medical  Botany;  or,  a  Description  of  all  the  more  im- 
portant Plants  used  in  Medicine,  and  of  their  properties,  Uses,  and  Modes  of  Administra- 
tion. In  one  large  octavo  volume  of  704  pages,  handsomely  printed,  with  nearly  350 
illustrations  on  wood. 

GARDNER  (D.  PEREIRA),  M.D.— Medical  Chemistry,  for  the  use  of  Students  and  the  Pro- 
fession :  being  a  Manual  of  the  Science,  with  its  Applications  to  Toxicology',  Physiology, 
Thsrapeutics,  Hygiene,  &c.    In  one  handsome  royal  12mo.  volume,  with  illustrations. 


HARRISON  (.JOHN),  M.  D.  —  An  Essay  towards  a  Correct  Theory  of  the  Nervous  System. 
In  one  octavo  volume,  292  pages. 


HUGHES  (H.  M.),  M.  D.  —  A  Clinical  Introduction  to  the  Practice  of  Auscultation,  and 
other  Modes  of  Physical  Diagnosis,  in  Diseat^es  of  the  Lungs  and  Heart.  Second  American 
from  the  second  and  improved  London  edition.    In  one  royal  12mo.  volume. 


HORNER  (WILLIAM  E.),  M.  D.  —  Special  Anatomy  and  Histology.  Eighth  edition.  Ex- 
tensively revised  and  modified.  In  two  large  octavo  volumes,  of  more  than  1000  pages, 
handsomely  printed,  with  over  300  illustrations. 


HOBLYN  (RICHARD  D.),  A.M.— A  Dictionary  of  the  Terms  used  in  Medicine  and  the  Col- 
lateral Sciences.  Second  and  improved  American  edition.  Revised,  with  numerous  Ad- 
ditions, from  the  second  London  edition,  by  Isaac  Hays,  M.  D.,  &c.  In  one  large  royal 
12mo.  volume,  of  over  500  pages,  double  columns.    {Now  Ready.) 


HABERSHON  (S.  0.),  M.  D.— Pathological  and  Practical  Observations  on  Diseases  op  thr 
Alimentary  Canal.  (Esophagus,  Stomach,  C(ecum,  and  iNTEiTiNES.    With  illustrations  on 
wood.     In  one  handsome  octavo  volume. 
***  Publishing  in  th«  "Medical  New*  and  Library"  for  1858. 


BLANCHARD  &  LEA'S  MEDICAL  PUBLICATIONS.  7 

HAMILTON  (FRANK  11.)— A  TRKAnsE  ox  Fractdres  and  Dislocations.    In  one  handsome 
octavo  volume.    With  numerous  illustrations.    (I^eparing.) 


HOLLAND  (SIR  HENRY),  M.  D.— Medical  Notes  and  Reflections.    From  the  third  London 
edition.    In  one  handsome  octavo  volume,  extra  cloth,  of  about  500  pages.    (Just  Issued.) 


JONES  (T.  WHARTON),  F.  R.  S.— The  Principles  and  Practice  of  OrnTHALMic  Medicine  and 
SURGERT.  Second  American,  from  the  second  and  revised  English  edition.  With  Additions 
by  Edward  Hartshorne,  M.  D.  In  one  very  neat  volume,  large  royal  12mo.,  of  500  pages, 
with  110  illustrations. 


JONES  (C.  HANDFIELD),  F.  R.  S.,  AND  EDWARD  H.  SIEVEKING,  M.D.  — A  Manual  op 
Pathological  Anatomy.  With  397  engravings  on  wood.  In  one  handsome  volume,  octavo, 
of  nearly  750  pages,  leather.    {Lately  Issiieil.) 


KIRKES  (WILLIAM  SENHOUSE),  M.  D.,  AND  JAMBS  PAGET,  F.R.S.  — A  Manual  op 
PuTsioLOGT.  Third  American,  from  the  third  and  improved  London  edition.  With  200 
illustrations.    In  one  large  and  handsome  royal  12mo.  volume.    588  pages.    (^Now  Ready.) 


KNAPP  (F.),  Pn.  D.— Technologt  ;  or,  Chemistry  applied  to  the  Arts  and  to  Manufactures. 
Edited,  with  numerous  Notes  and  Additions,  by  Dr.  Edmund  Ronalds  and  Dr.  Thomas 
Richardson.  First  American  edition,  with  Notes  and  Additions,  by  Professor  Walter  R. 
Johnson.  In  two  handsome  octavo  volumes,  printed  and  illustrated  in  the  highest  style 
of  art,  with  about  500  wood-engravings. 


LEHMANN  (G.  C.)  —  Phtsiological  Chemistry,  Translated  from  the  second  edition  by 
George  E.  Day,  M.  D.  Edited  by  R.  E.  Rogers,  M.  D.  With  illustrations  selected  from 
Funke's  Atlas  of  Physiological  Chemistry,  and  an  Appendix  of  Plates.  Complete  in  two 
handsome  octavo  volumes,  extra  cloth,  containing  1200  pages.  With  nearly  200  illustra- 
tions.   (Just  Issued.) 


LEHMANN  (G.  C.).  — Manual  of  Chemical  Physiology.  Translated  from  the  German,  with 
Notes  and  Additions,  by  J.  C.  Morris,  M.  D.  With  an  introductory  Essay  on  Vital  Force, 
by  Samuol  .Jackson,  M.  D.  In  one  handsome  octavo  volume,  extra  cloth,  of  336  pages. 
With  numerous  illustrations. 


LA  ROCHE  (R.),  M.D.— Pneumonia;  its  Supposed  Connection,  Pathological  and  Etiological, 
with  Autumnal  Fevers,  including  an  Inquiry  into  the  Existence  and  Morbid  Agency  of 
Malaria.    In  one  handsome  octavo  volume,  extra  cloth,  of  500  pages. 


LA  ROCHE  (R.),  M.  D.— Yellow  Fever,  considered  in  its  Historical,  Pathological,  Etiological, 
and  Therapeutical  Relations.  Includiug  a  Sketch  of  the  Disease  as  it  has  occurred  in 
Philadelphia  from  1090  to  1851,  with  an  Examination  of  the  Connections  between  it  and 
the  Fevers  known  under  the  same  name  in  other  I'arts  of  Temperate,  as  well  as  in  Tropical 
ISegions.  In  two  large  and  handsome  octavo  volumes,  of  nearly  1500  pages,  extra  cloth. 
(Just  Issued.) 


LAWRENCE  (W.),  F.  R.  S.  —  A  Treatise  on  Diseases  op  the  Eye.  A  new  edition,  edited, 
with  numerous  Additions,  and  243  illustrations,  by  Isaac  Hays,  M.  D.,  Surgeon  to  Wills' 
Hospital,  etc.  In  one  very  large  and  handsome  octavo  volume  of  950  pages,  strongly 
bound  in  leather,  with  raised  bands. 


LUDLOW  (J.  L.),  M.  D.  —  A  Manual  of  Examinations  upon  Anatomy,  Physiology,  Surgery, 
Practice  of  Medicine,  Obstetrics,  Materia  Medica,  Chemistry,  Pharmacy,  and  Thera- 
peutics. To  which  is  added,  a  Medical  Formulary.  Third  edition,  thoroughly  revised  and 
greatly  extended  and  enlarged.  With  370  illustrations.  In  one  large  and  handsome  royal 
12mo.  volume,  leather,  of  over  800  pages.     (Just  Iss^ued.) 


LAYCOCK  (THOMAS),  M.  D.— Lectures  on  the  Principles  and  Methods  op  Medical  Obskrt 
YATioN  AND  Research.    In  ens  very  B«at  royal  12uio.  volume,  «xtru  cloth.    (Just  Issued.) 


B  BLANCHARD  &  LEA'S  MEDICAL  PUBLICATIONS. 

LA'tiLBMAND  (M.).— The  Causes,  Symptoms,  and  Treatment  of  Spermatorbhcea.  Translated 
and  edited  by  Henry  J.  McDougal.  In  one  volume,  octavo,  of  ii20  pages.  Second  Aiuo- 
rican  edition. 


LARDNER  (DTONYSIUS),  D.C.L. — Handbooks  op  Natubal  Philosophy  and  Astronomy. 
Revised,  with  numerous  Additions,  by  the  American  editor.  First  Course,  containing 
Mechanics,  Hydrostatics,  Hydraulics,  Pneumatics,  Sound,  and  Optics.  In  one  large  royal 
12mo.  volume,  of  750  pages,  with  424  wood-cuts.  Secont)  Course,  containing  Heat,  Elec- 
tricity, Magnetism,  and  Galvanism,  one  volume,  large  royal  12mo.,  of  450  pages,  with  250 
illustrations.  Third  Course  (now  ready),  containing  Meteorology  and  Astronomy,  in  one 
large  volume,  royal  12mo.,  of  nearly  800  pages,  with  37  plates  and  200  wood-cuts.  Tlie 
•whole  complete  in  three  volumes,  of  about  2000  large  pages,  with  over  1000  figures  on  stool 
and  wood. 


MEIGS  (CHARLES  D.),  M.D.— Woman:  her  Diseases  and  their  Remedies.  A  Series  of  Leo 
turea  to  his  Class.  Third  and  improved  edition.  In  one  large  and  beautifully-printed 
octavo  volume. 


HEIGS  (CHARLES  D.),  M.  D.  —  Obstetrics  :  the  Science  and  the  Art.  Second  edition, 
revised  and  improved.  "With  131  illustrations.  In  one  beautifully-printed  octavo  volume, 
of  752  large  pages. 


MEIGS  (CHARLES  D.),  M.  D.  —  A  Treatise  on  Acute  and  Chronic  Diseases  op  the  Neck  op 
THE  Uterus.  With  numerous  plates,  drawn  and  colored  from  nature,  in  the  highest  style 
of  art.    In  one  handsome  octavo  volume,  extra  cloth. 


MEIGS  (CHARLES  D.),  M.D.— On  the  Nature,  Signs,  and  Treatment  of  Childbed  Fever, 
in  a  Series  of  Letters  addressed  to  the  Students  of  his  Class.  In  one  handsome  octavo 
volume,  extra  cloth,  of  365  pages. 


JIILLER  (JAMES),  F.  R.  S.  E.— Principles  of  Surgery.  Fourth  American,  from  the  third 
and  revised  Edinburgh  edition.  In  one  large  and  very  beautiful  volume  of  700  pages,  with 
240  exquisite  illustrations  on  wood. 


MILLER  (JAMES),  F.  R.  S.  E. — The  Practice  op  Surgery.  Fourth  American,  from  the  third 
Edinburgh  edition.  Edited,  with  Additions.  Illustrated  by  304  engravings  on  wood.  In 
one  large  octavo  volume  of  over  700  pages. 


MALGATGNE  (J.  F.).  —  Operative  Surgery,  based  on  Normal  and  Pathological  Anatomy. 
Translated  from  the  French,  by  Frederick  Brittan,  A.  B.,  M.  D.  With  numerous  illustra- 
tions on  wood.    In  one  handsome  octavo  volume  of  nearly  600  pages. 


MOHR  (FRANCIS),  Ph.  D.,  AND  REDWOOD  (THEOPHILUS).— Practical  Pharmacy.  Com- 
prising the  Arrangements,  Apparatus,  and  Manipulations  of  the  Pharmaceutical  Shop  and 
Laboratory.  Edited,  with  extensive  Additions,  by  Prof.  William  Procter,  of  the  Philadel- 
phia College  of  Pharmacy.  In  one  handsomely-printed  octavo  volume,  of  570  pages,  with 
over  500  engravings  on  wood. 


JfACLTSE  (JOSEPH). — Surgical  Anatomy.  Forming  one  volume,  very  large  imperial  quarto. 
With  sixty-eight  large  and  splendid  Plates,  drawn  in  the  best  style,  and  beaiitifully  colort'd. 
Containing  190  Figures,  many  of  them  the  size  of  life.  Together  with  copious  and  expla- 
natory letter-press.  Strongly  and  handsomely  lx)und  in  extra  cloth,  being  one  of  tlio 
cheapest  and  best  executed  Surgical  works  as  yet  issued  in  this  country. 

Copies  can  be  sent  by  mail,  in  five  parts,  done  up  in  stout  covers. 


MILLER  (HENRY),  M.  D.  —  Principles  and  Practice  op  Obstetrics;  including  the  Treat- 
iiK^nt  of  Chronic  Inflammation  of  tlie  Cervix  and  Body  of  the  Uterus,  considered  as  a  fre- 
quent (.'ause  of  Abortion.  With  about  100  engravings  on  wood.  In  one  very  handsenje 
octavo  volume  of  over  600  pages.     (Noio  Ready.) 


BLANCHARD  A  LEA'S  MEDICAL  PUBLICATIONS.  0 

MONTGOMERY  (W.  F.),  M.  D.,  Ac  — Ax  Exposition  op  the  Signs  and  Stmptobis  of  Preg- 
nancy. With  some  other  Papers  on  Subjects  connected  with  Midwifery.  From  the  second 
and  enlarjited  English  edition.  With  two  exquisite  coloured  plates  and  numerous  wood- 
cuts. In  one  very  handsome  octavo  volume,  extra  cloth,  of  nearly  600  pages.   {JVoio  Heady.) 


MAYNE  (JO FIN),  M.D.— A  DispensaTOrt  and  Therapeuticai,  Remembrancer.  Comprising 
the  entire  lists  of  Materia  Medica,  with  every  Practical  Formula  contained  in  the  three 
British  Pharmacopoeias.    In  one  12mo.  volume,  extra  cloth,  of  over  300  large  pages. 

MACKENZIE  (W.),  M.  D.  —  A  Practical  Treatise  on  Diseases  and  Injuries  of  the  Eye.  To 
which  is  prefixed  an  Anatomical  Introduction,  by  T.  Wharton  Jones.  From  the  fourth 
revised  and  enlarged  London  edition.  With  Notes  and  Additions  by  Addinell  Ilewson, 
M.  I).  In  one  very  large  and  handsome  octavo  volume,  with  numerous  wood-cuts  and 
plates.    1028  pages,  leather,  raised  bands.    {Just  Issued.) 


NEILL  (JOHN),  M.  D.,  AND  FRANCIS  GURNEY  SMITH,  M.  D.— An  Analytical  Compen- 
dium OF  THE  Various  BnANcnES  op  Medical  Science;  for  the  Use  and  Examination  of  Stu- 
dents. Second  edition,  revised  and  improved.  In  one  very  large  and  handsomely  printed 
royal  12mo.  volume  of  over  1000  pages,  with  350  illustrations  on  wood.  Strongly  bound 
in  leather,  with  raised  bands. 

NEILL  (JOHN),  M.  D. — Outlines  of  the  Nerves.  1  vol.  8vo.,  with  handsome  plates.  Out- 
UNES  of  the  Veins  and  Lymphatics,  1  vol.  8vo.,  handsome  colored  plates. 


NELIGAN  (J.  MOORE),  M.D.  — Atlas  of  Cutaneous  Diseases.  In  one  beautiful  quarto 
volume,  extra  cloth,  with  splendid  colored  plates,  presenting  nearly  one  hundred  elaborate 
representations  of  disease.    {Now  Ready.) 


NELIGAN  (J.  MOORE),  51.  D.  —A  Practical  Treatise  on  Diseases  of  the  Skin.    In  one  neat 
royal  12mo.  volume,  of  334  pages. 


OWEN  (PROF.  R.)  —  On  the  Different  Forms  of  the  Skeleton.    One  royal  12mo.  volume, 
with  numerous  illustrations. 


PARKER  (LANG STON).— The  Modern  Treatment  of  Syphilitic  Diseases,  both  primary  and 
Secondary;  comprLsing  the  Treatment  of  Constitutional  and  Confirmed  Syphilis,  by  a  safe 
and  successful  method.  With  numerous  Cases,  Formulae,  and  Clinical  Observations. 
From  the  third  and  entirely  rewritten  London  edition.    In  one  neat  octavo  volume. 


PEREIR A  (JONATHAN),  M.  D.  —  The  Elements  op  Materia  Medica  and  Therapeutics. 
Third  American  edition,  enlarged  and  improved  by  the  author;  including  Notices  of  most 
of  the  Medical  Substances  in  use  in  the  civilized  world,  and  forming  an  Encyclopaedia  of 
Materia  Medica.  Edited,  with  Additions,  by  Joseph  Carson,  M.  D.,  Professor  of  Materia 
Medica  and  Pharmacy  in  the  University  of  Pennsylvania.  In  two  very  large  octavo  vo- 
lumes of  2100  pages,  on  small  type,  with  over  450  illustrations.    {Now  Complete.) 


PARRISII  (EDWARD).— An  Introduction  to  Practical  Pharmacy.  Designed  as  a  Text-book 
for  the  Student,  and  as  a  Guide  for  the  Physician  and  Pharmaceutist.  With  many  For- 
mulae and  Prescriptions.  In  one  handsome  octavo  volume,  extra  cloth,  of  550  pages,  with 
243  illustrations. 


PEASELEE  (E.  R.),  M.  D. — Human  Histology,  in  its  Applications  to  Physiology  and  General 
Pathology.    With  434  illustrations.    In  one  handsome  octavo  volume.    {Now  Ready.) 


PIRRTE  (WILLIAM),  F.E.S.E.— The  Principles  and  Practice  of  Surgery.  Edited  by  John 
Neill,  M.D.,  Demonstrator  of  Anatomy  in  the  University  of  Pennsylvania,  Surgeon  to  the 
Pennsylvania  Hospital,  &c.  In  one  very  handsome  octavo  volume  of  780  pages,  with  316 
illustrations. 


RAMSBOTHAM  (FRANCIS  H.),  M.  D.— The  Principles  and  Practice  of  Obstetric  Medicine 
AND  Surgery,  in  reference  to  the  Process  of  Parturition.  A  new  and  enlarged  edition,  tho- 
roughly revised  by  the  author.  With  Additions  by  W.  V.  Keating,  M.  D.  In  one  large 
and  hiindsome  imperial  octavo  volume  of  050  pages,  strongly  bound  in  leather,  with  raided 
bands.  With  sixty-four  beautiful  plates,  and  numerous  wood-cuts  in  the  text,  containing 
in  all  nearly  200  large  and  beautiful  figutcs.     {Just  Issued.) 


RTCiBY  (EDWARD),  :M.  D.— Ox  the  Constitutional  Treatment  of  Female  Diseases.    In  on© 
neat  royal  12mo.  volume,  extra  cloth,  of  about  250  pages.    {Just  Issued.) 


10  BLANCIIARD  A  LEA'S  MEDICAL  PUBLICATIONS. 

RICOBD  (P.),  M.D.— Illustrations  of  Syphilitic  Disease.  Translated  from  the  French,  by 
Thomas  F.  Betton,  M.  D.  With  the  addition  of  a  History  of  Syphilis,  and  a  complete  Bihli 
on;raphy  and  Formulary  of  Eemedies,  collated  and  arranged  by  Paul  B.  Goddard,  M.D. 
With  fifty  large  quarto  plates,  comprising  117  beautifully  colored  illustrations.  In  one 
large  and  handsome  quarto  volume. 


KICORD  (P.),  M.D.— A  Treatise  on  the  Venereal  Disease.  By  John  Hunter,  F.  R.  S.  With 
copious  Additions,  by  Ph.  Ricord,  M.D.  Edited,  with  Notes,  by  Freeman  J.  Bumstead, 
M.D.    In  one  handsome  octavo  volume,  with  plates. 


EICORD  (P.),  M,  D.— Letters  on  Stphilis,  addressed  to  the  Chief  Editor  of  the  Union  Medi- 
cale.  With  an  Introduction,  by  Am6dee  Latour.  Translated  by  W.  P.  Lattimore,  M.  D. 
In  one  neat  octavo  volume. 


ROKITANSKY  (CARL). — A  !^UNUAL  op  Pathological  Anatomy.  Translated  from  the  Ger- 
man by  W.  E.  Swaine,  Edward  Sieveking,  M.D.,  C.  H.  Moore,  and  George  E.  Day,  M.D. 
Complete,  four  volumes  bound  in  two,  extra  cloth,  of  about  1200  pages.    {Jtut  Issued.) 


RIGBY  (EDWARD),  M.  D.— A  System  of  Midwifery.    With  Notes  and  Additional  Illustra- 
tions.   Second  American  edition.    One  volume  octavo,  422  pages. 


ROYLE  (J.  FORBES),  M.D. — Materia  Medica  and  Therapeutics;  including  the  Preparations 
of  the  Pharmacopoeias  of  London,  Edinburgh,  Dublin,  and  of  the  United  States.  With 
many  new  Medicines.  Edited  by  Joseph  Carson,  M.D.,  Professor  of  Materia  Medica  and 
Pharmacy  in  the  University  of  Pennsylvania.  With  ninety-eight  illustrations.  In  one 
large  octavo  volume  of  about  700  pages. 


SEEY  (FREDERICK  C),  F.  R.  S.— Operative  Surgery.   In  one  very  handsome  octavo  volume 
of  over  650  pages,  with  about  100  wood-cuts. 


BHARPEY  (WILLIAM),  M.  D.,  JONES  QUAIN,  M.  D.,  AND  RICHARD  QUAIN,  F.  R.  S.,  etc.— 
Human  Anatomy.  Revised,  with  Notes  and  Additions,  by  Joseph  Leidy,  M.D.  Complete 
in  two  large  octavo  volumes,  of  about  1300  pages.  Beautifully  illustrated  with  over  500 
engravings  on  wood. 


SMITH  (HENRY  H.),  M.D.,  AND  WILLIAM  E.  HORNER,  M.D.— An  Anatomical  ATLj«a 
illustrative  of  the  Structure  of  the  Human  Body.  In  one  volume,  large  imperial  octavo, 
with  about  660  beautiful  figures. 


BMITH  (HENRY  H.),  M.D.— Minor  Surgery;  or.  Hints  on  the  Everyday  Duties  of  the 
Surgeon.  With  247  illustrations.  Third  and  enlarged  edition.  In  one  handsome  royal 
12mo.  volume  of  456  pages 


SARGENT  (F.  W.),  M.D.- On  Bandagino  and  other  Operations  of  Minor  Surgery.  Second 
edition,  enlarged.  In  one  handsome  royal  12mo.  volume  of  nearly  400  pages,  with  182 
illustrations.    (Just  Issued.) 

STTLL:6  (ALFRED),  M.  D.— PsiNaPLES  OF  Therapeutics.  In  one  handsome  volume.  (Pre- 
paring^ 


SIMON  (JOHN),  F.R.  S.— General  Pathology,  as  conducive  to  the  E.<!tablishment  of  Rational 
Priticiples  for  the  Prevention  and  Cure  of  Disease.  A  Course  of  Lectures  delivered  at  SL 
Thomas's  Hospital  during  the  Summer  Session  of  1850.    In  one  neat  octavo  volume. 


SMITH  (W.  TYLER),  M.D.— On  Parturition,  and  the  Principles  and  Practice  of  Obstetrics 
In  one  large  duodecimo  volume  of  400  pages. 

^^riTH  (W.  TYLER),  M.D.— The  Patholooy  and  Treatment  op  LEUOORRHffiA.    With  nume- 
rous illustrations.    In  one  very  handsomu  octavo  volum*,  extra  cloth,  of  about  250  paffos. 


BLANCHARD  &  LEA'S  MEDICAL  PUBLICATIONS.  11 

SOLLY  (SAMUEL),  F.R.S.  — The  Human  Brain;  its  Structure,  Physiology,  and  Diseases 
With  a  Description  of  the  Typical  Forms  of  the  Brain  in  the  Animal  Kingdom.  From  th« 
Second  and  much  enlarged  London  edition.    In  one  octavo  volume,  with  120  wood-cuts. 


SCHCEDLER  (FRIEDRICH),  Ph.D.— TnE  Book  op  Nature;  an  Elementary  Introduction  to 
the  Sciences  of  Physics,  Astronomy,  Chemistry,  Mineralogy,  Geology.  Botany,  Zoology,  and 
Physiology.  First  American  edition,  with  a  Glossary  and  other  Additions  and  Improve- 
ments; from  the  second  English,  edition.  Translated  fronJ  the  sixth  German  edition,  hy 
Henry  Medlock,  F.C.S.,  &c.  In  one  thick  volume,  small  octavo,  of  ahout  700  pages,  with 
r)79  illustrations  on  wood.  Suitable  for  the  higher  schools  and  private  students.  (iVino 
Heady.) 

TAYLOR  (ALFRED  S.),  M.  D.,  F.  R.  S.— Medical  JtmiSPRCDENOB.  Fotirth  American,  from  the 
fifth  and  improved  English  edition.  With  Notes  and  References  to  American  Decisions, 
by  Edward  Hartshorne,  M.  D.    In  one  large  octavo  volume  of  700  pages.    (Now  Ready.) 


TAYLOR  (ALFRED  S.),  M.  D.— On  Poisons,  in  Relation  to  Medical  Jurisprudencb  and  Medi- 
CTNE.  Edited,  with  Notes  and  Additions,  by  R.  E.  Griffith,  M.D.  In  one  large  octavo 
volume  of  688  pages. 


TANNER  (T.  H.).  M.  D.— A  M.\ntjal  op  Clinical  Medicine  and  Physical  Diaqnosis.  To  which 
is  addfd.  The  Code  of  Ethics  of  the  American  Medical  Association.  In  one  neat  volume, 
small  12mo.,^extra  cloth,  or  flexible.    {Just  Issued.) 

TODD  (R.  B.),  M.  D.— Clinical  Lectures  on  Certain  Diseases  op  the  Urinary  Organs,  and 
ON  Dropsies.    In  one  octavo  volume,  extra  cloth,  of  about  300  pages.    {Just  Issued.) 


TODD  (R.  B.),  M.  D.,  AND  WILLIAM  BOWMAN,  F.  R.  S.— Physiological  Anatomy  and  Phy- 
siology OP  Man.  Now  complete,  in  one  very  large  and  handsome  octavo  volume,  of  926 
pages,  with  300  illustrations  on  wood.    {Just  Issiicd,  1857.) 

JJSS^  Gentlemen  who  have  the  earlier  portions  of  this  work  can  still  complete  their  copies, 
if  early  application  be  made. 


WATSON  (THOMAS),  M.  D.,  Ac. —  Lectures  on  the  principles  and  Practice  of  physic. 
A  new  American,  from  the  last  London  edition.  Revised,  with  Additions,  by  D.  Francis 
Condie,  M.  D.,  author  of  a  "Treatise  on  the  Diseases  of  Children,"  Ac.  In  one  Octavo 
volume,  of  nearly  1100  large  pages,  strongly  bound,  with  raised  bands. 


WALSHE  (W.  H.),  M.  D.— Diseases  op  the  Heart,  Lungs,  and  Appendages;  their  Symptoms 
and  Treatment.    In  one  handsome  volume,  large  royal  12mo.,  512  pages. 


What  to  Observe  at  the  Bedside  and  after  Death,  in  Medical  Cases.  Published  under  the 
authority  of  the  London  Society  for  Medical  Observation.  In  one  very  handsome  volume, 
royal  12mo.,  extra  cloth. 


WILDE  (W.  R.).— Aural  Surgery,  and  the  Nature  and  Treatment  op  Diseases  op  the  Ear. 
In  one  handsome  octavo  volume,  with  illustrations. 


WHITEHEAD  (J AMES),  F.  R.  C.  S.,  &c  — The  Causes  and  Treatment  op  Abortion  and  Ste- 
rility;  being  the  Result  of  an  Extended  Practical  Inquiry  into  the  Physiological  and 
Morbid  Conditions  of  the  Uterus.  Second  American  Edition.  In  one  volume,  octavo,  308 
pages 


WEST  (CHARLES),  M.D.— Lectures  on  the  Diseases  of  Infancy  and  Childhood.    Seoond 
American,  from  the  second  and  enlarged  London  edition.    In  one  volame,  octavo,  of  nearly 

600  pages. 


12  BLANCHARD  &  LEA'S  MEDICAL  PUBLICATIONS. 

WEST  (CirARLES),  M.  D. — An  Inquiry  into  the  Pathological  Importance  of  Ulceration  of 
THE  Os  Uteri.  Being  the  Croonian  Lectures  for  the  year  1854.  In  one  neat  octavo  to- 
lume,  extra  cloth. 


WEST  (CHARLES),  M. D.  —  Lectures  on  the  Diseases  of  Women.  In  two  Parts.  Parti., 
Diseases  of  the  Uterus.  Part  II.,  Diseases  of  the  Ovaries,  &c.,  the  Bladder,  Vagina,  and 
External  Organs. 

Part  I.  now  ready,  1  vol.  8vo.,  extra  doth,  of  about  300  pages. 


WILSON  (ERASMUS),  M.  D.,  F.  R.  S.— A  System  of  Human  Anatomy,  General  and  Special. 
Fourth  American,  from  the  last  English  edition.  Edited  by  Paul  B.  Goddard,  A.  M.,  M.  D. 
With  250  illustrations.  Beautifully  printed,  in  one  large  octavo  volume,  of  nearly  600 
pages. 


WILSON  (ERASMUS),  M.  D.,  F.  R.  S.— The  Dissector's  Manual;  Practical  and  Surgical  Ana- 
tomy. Third  American,  from  the  last  revised  and  enlarged  English  edition.  Modified  and 
re-arranged  by  William  Hunt,  M.  D.  In  one  large  and  handsome  royal  12mo.  volume, 
leather,  of  582  pages,  with  154  illustrations.    (Now  Heady.) 


WILSON  (ERASMUS),  M.  D.,  F.  R.  S.— On  Diseases  of  the  Skin.  Fourth  American,  from  the 
Fourth  London  edition.    In  one  neat  octavo  volume,  of  650  pages,  extra  cloth. 

Also,  An  Atlas  op  Plates,  of  which  twelve  are  exquisitely  coloured,  illustrating  "  Wilson  on 
THE  Skin."     8vo.,  cloth.     (Now  Ready.) 


WILSON  (ERASMUS),  M.  D.,  F.  R.  S. — On  Constitutional  and  ITeret»itary  Syphilus,  and  on 
Syphilitic  Eruptions.  In  one  small  octavo  volume,  beautifully  printod,  with  four  exqui- 
site coloured  plates,  presenting  more  than  thirty  varieties  of  Syphilitic  Eruptions. 


WILSON  (ERASMUS),  M.  D.,  F.  R.  S.— Healthy  Skin;  a  Treatise  on  the  Management  of  the 
Skin  and  Ilair  in  Relation  to  Health.  Second  American,  from  the  fourth  and  improved 
London  edition.  In  one  handsome  royal  r2mo.  volume,  extra  cloth,  with  numerous  illus- 
trations.   Copies  may  also  be  had  in  paper  covers,  for  mailing,  price  75  cents. 


WILLIAMS  (C.  J.  B.),  M.D.,  F.R.S.— Principles  of  Medicine;  comprising  General  Pathology 
and  Tl'^fapeutics,  and  a  brief  General  View  of  Etiology,  Nosology,  Semeiology,  Diagnosis, 
Prognosis,  and  Ilygienics.  Fifth  American,  from  a  new  and  enlarged  London  edition. 
In  one  octavo  volume,  of  500  pages. 


YOU  ATT  (WILLIAM),  V.  S.  — The  Horse.  A  new  edition,  with  numerous  illustrations; 
together  with  a  General  History  of  the  Horse;  a  Dissertation  on  the  American  Trotting 
Horse;  how  Trained  and  Jockeyed ;  an  account  of  his  Remarkable  Performances;  and  an 
Essay  on  the  Ass  and  the  Mule.  By  J.  S.  Skinner,  formerly  Assistant  Postmaster-General, 
and  Editor  of  the  Turf  Register.    One  large  octavo  volume. 


you  ATT  (WILLIAM),  V.  S.— The  Doo.    Edited  by  E.  J.  Lewis,  M.  D.    With  numerous  and 
beautiful  illustrations.    In  one  very  handsome  volume,  crown  8vo.,  crimson  cloth,  gilt. 


IllwstratelJ  €ihU^M. 


Blanchard  &  Lea  have  now  ready  a  detailed  Catalogue  of  their  publications,  in  Medical  and 
other  Sciences,  with  Specimens  of  the  Wood-engravings,  Notices  of  the  Press.  &c.  &c.,  forming 
a  pamphlet  of' eighty  large  octavo  pages.  It  has  been  prepared  without  regard  to  expense, 
and  may  be  considered  as  one  of  the  handsomest  specimens  of  printing  as  yet  executed  in 
this  country.    Copies  will  be  sent  free,  by  post,  on  receipt  of  nine  cents  in  postage  stamps. 

Detailed  Catalogues  of  their  publications,  Miscellaneous,  Educational,  Medical,  i-c,  fur- 
nished gratis,  on  application. 


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